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Man Pages


Manual Reference Pages  -  TK::CANVAS (3)

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NAME

Tk::Canvas - Create and manipulate Canvas widgets

CONTENTS

SYNOPSIS

$canvas = $parent-><B>CanvasB>(?options?);

STANDARD OPTIONS

<B>-backgroundB> <B>-highlightthicknessB> <B>-insertwidthB>        <B>-stateB> <B>-borderwidthB>        <B>-insertbackgroundB>   <B>-reliefB>     <B>-tileB> <B>-cursorB>     <B>-insertborderwidthB>  <B>-selectbackgroundB>   <B>-takefocusB> <B>-highlightbackgroundB>        <B>-insertofftimeB>      <B>-selectborderwidthB>  <B>-xscrollcommandB> <B>-highlightcolorB>     <B>-insertontimeB>       <B>-selectforegroundB>   <B>-yscrollcommandB>

WIDGET-SPECIFIC OPTIONS

Name:  <B>closeEnoughB>
Class: <B>CloseEnoughB>
Switch:        <B>-closeenoughB> Specifies a floating-point value indicating how close the mouse cursor must be to an item before it is considered to be ‘‘inside’’ the item. Defaults to 1.0.
Name:  <B>confineB>
Class: <B>ConfineB>
Switch:        <B>-confineB> Specifies a boolean value that indicates whether or not it should be allowable to set the canvas’s view outside the region defined by the <B>scrollRegionB> argument. Defaults to true, which means that the view will be constrained within the scroll region.
Name:  <B>heightB>
Class: <B>HeightB>
Switch:        <B>-heightB> Specifies a desired window height that the canvas widget should request from its geometry manager. The value may be specified in any of the forms described in the COORDINATES section below.
Name:  <B>scrollRegionB>
Class: <B>ScrollRegionB>
Switch:        <B>-scrollregionB> Specifies a list with four coordinates describing the left, top, right, and bottom coordinates of a rectangular region. This region is used for scrolling purposes and is considered to be the boundary of the information in the canvas. Each of the coordinates may be specified in any of the forms given in the COORDINATES section below.
Name:  <B>stateB>
Class: <B>StateB>
Switch:        <B>-stateB> Modifies the default state of the canvas where state may be set to one of: normal, disabled, or hidden. Individual canvas objects all have their own state option, which overrides the default state. Many options can take separate specifications such that the appearance of the item can be different in different situations. The options that start with active control the appearence when the mouse pointer is over it, while the option starting with disabled controls the appearence when the state is disabled.
Name:  <B>widthB>
Class: <B>widthB>
Switch:        <B>-widthB> Specifies a desired window width that the canvas widget should request from its geometry manager. The value may be specified in any of the forms described in the COORDINATES section below.
Name:  <B>xScrollIncrementB>
Class: <B>ScrollIncrementB>
Switch:        <B>-xscrollincrementB> Specifies an increment for horizontal scrolling, in any of the usual forms permitted for screen distances. If the value of this option is greater than zero, the horizontal view in the window will be constrained so that the canvas x coordinate at the left edge of the window is always an even multiple of <B>xScrollIncrementB>; furthermore, the units for scrolling (e.g., the change in view when the left and right arrows of a scrollbar are selected) will also be <B>xScrollIncrementB>. If the value of this option is less than or equal to zero, then horizontal scrolling is unconstrained.
Name:  <B>yScrollIncrementB>
Class: <B>ScrollIncrementB>
Switch:        <B>-yscrollincrementB> Specifies an increment for vertical scrolling, in any of the usual forms permitted for screen distances. If the value of this option is greater than zero, the vertical view in the window will be constrained so that the canvas y coordinate at the top edge of the window is always an even multiple of <B>yScrollIncrementB>; furthermore, the units for scrolling (e.g., the change in view when the top and bottom arrows of a scrollbar are selected) will also be <B>yScrollIncrementB>. If the value of this option is less than or equal to zero, then vertical scrolling is unconstrained.

DESCRIPTION

The <B>CanvasB> method creates a new window (given by the $canvas argument) and makes it into a canvas widget. Additional options, described above, may be specified on the command line or in the option database to configure aspects of the canvas such as its colors and 3-D relief. The <B>canvasB> command returns its $canvas argument. At the time this command is invoked, there must not exist a window named $canvas, but $canvas’s parent must exist.

Canvas widgets implement structured graphics. A canvas displays any number of items, which may be things like rectangles, circles, lines, and text. Items may be manipulated (e.g. moved or re-colored) and callbacks may be associated with items in much the same way that the bind method allows callbacks to be bound to widgets. For example, a particular callback may be associated with the <B><Button-1>B> event so that the callback is invoked whenever button 1 is pressed with the mouse cursor over an item. This means that items in a canvas can have behaviors defined by the Callbacks bound to them.

DISPLAY LIST

The items in a canvas are ordered for purposes of display, with the first item in the display list being displayed first, followed by the next item in the list, and so on. Items later in the display list obscure those that are earlier in the display list and are sometimes referred to as being ‘‘on top’’ of earlier items. When a new item is created it is placed at the end of the display list, on top of everything else. Widget methods may be used to re-arrange the order of the display list.

Window items are an exception to the above rules. The underlying window systems require them always to be drawn on top of other items. In addition, the stacking order of window items is not affected by any of the canvas methods; you must use the raise and lower Tk widget methods instead.

ITEM IDS AND TAGS

Items in a canvas widget may be named in either of two ways: by id or by tag. Each item has a unique identifying number which is assigned to that item when it is created. The id of an item never changes and id numbers are never re-used within the lifetime of a canvas widget.

Each item may also have any number of tags associated with it. A tag is just a string of characters, and it may take any form except that of an integer. For example, ‘‘x123’’ is OK but ‘‘123’’ isn’t. The same tag may be associated with many different items. This is commonly done to group items in various interesting ways; for example, all selected items might be given the tag ‘‘selected’’.

The tag <B>allB> is implicitly associated with every item in the canvas; it may be used to invoke operations on all the items in the canvas.

The tag <B>currentB> is managed automatically by Tk; it applies to the current item, which is the topmost item whose drawn area covers the position of the mouse cursor. If the mouse is not in the canvas widget or is not over an item, then no item has the <B>currentB> tag.

When specifying items in canvas methods, if the specifier is an integer then it is assumed to refer to the single item with that id. If the specifier is not an integer, then it is assumed to refer to all of the items in the canvas that have a tag matching the specifier. The symbol tagOrId is used below to indicate that an argument specifies either an id that selects a single item or a tag that selects zero or more items.

tagOrId may contain a logical expressions of tags by using operators: ’&&’, ’||’, ’^’ ’!’, and parenthezised subexpressions. For example:

$c->find(’withtag’, ’(a&&!b)|(!a&&b)’);

or equivalently:

$c->find(’withtag’, ’a^b’);

will find only those items with either a or b tags, but not both.

Some methods only operate on a single item at a time; if tagOrId is specified in a way that names multiple items, then the normal behavior is for the methods is to use the first (lowest) of these items in the display list that is suitable for the method. Exceptions are noted in the method descriptions below.

COORDINATES

All coordinates related to canvases are stored as floating-point numbers. Coordinates and distances are specified in screen units, which are floating-point numbers optionally followed by one of several letters. If no letter is supplied then the distance is in pixels. If the letter is <B>mB> then the distance is in millimeters on the screen; if it is <B>cB> then the distance is in centimeters; <B>iB> means inches, and <B>pB> means printers points (1/72 inch). Larger y-coordinates refer to points lower on the screen; larger x-coordinates refer to points farther to the right.

TRANSFORMATIONS

Normally the origin of the canvas coordinate system is at the upper-left corner of the window containing the canvas. It is possible to adjust the origin of the canvas coordinate system relative to the origin of the window using the <B>xviewB> and <B>yviewB> methods; this is typically used for scrolling. Canvases do not support scaling or rotation of the canvas coordinate system relative to the window coordinate system.

Individual items may be moved or scaled using methods described below, but they may not be rotated.

INDICES

Text items support the notion of an index for identifying particular positions within the item.

Indices are used for methods such as inserting text, deleting a range of characters, and setting the insertion cursor position. An index may be specified in any of a number of ways, and different types of items may support different forms for specifying indices.

In a similar fashion, line and polygon items support index for identifying, inserting and deleting subsets of their coordinates. Indices are used for commands such as inserting or deleting a range of characters or coordinates, and setting the insertion cursor position. An index may be specified in any of a number of ways, and different types of items may support different forms for specifying indices.

Text items support the following forms for an index; if you define new types of text-like items, it would be advisable to support as many of these forms as practical. Note that it is possible to refer to the character just after the last one in the text item; this is necessary for such tasks as inserting new text at the end of the item. Lines and Polygons don’t support the insertion cursor and the selection. Their indices are supposed to be even always, because coordinates always appear in pairs.
number A decimal number giving the position of the desired character within the text item. 0 refers to the first character, 1 to the next character, and so on. If indexes are odd for lines and polygons, they will be automatically decremented by one. A number less than 0 is treated as if it were zero, and a number greater than the length of the text item is treated as if it were equal to the length of the text item. For polygons, numbers less than 0 or greater then the length of the coordinate list will be adjusted by adding or substracting the length until the result is between zero and the length, inclusive.
<B>endB> Refers to the character or coordinate just after the last one in the item (same as the number of characters or coordinates in the item).
<B>insertB> Refers to the character just before which the insertion cursor is drawn in this item. Not valid for lines and polygons.
<B>sel.firstB> Refers to the first selected character in the item. If the selection isn’t in this item then this form is illegal.
<B>sel.lastB> Refers to the last selected character in the item. If the selection isn’t in this item then this form is illegal.
<B>[B>x,y<B>]B> Refers to the character or coordinate at the point given by x and y, where x and y are specified in the coordinate system of the canvas. If x and y lie outside the coordinates covered by the text item, then they refer to the first or last character in the line that is closest to the given point. The Tcl string form @x,y is also allowed.

DASH PATTERNS

Many items support the notion of an dash pattern for outlines.

The first possible syntax is a list of integers. Each element represents the number of pixels of a line segment. Only the odd segments are drawn using the outline color. The other segments are drawn transparent.

The second possible syntax is a character list containing only 5 possible characters <B>[.,-_ ]B>, with the first 4 characters producing a segment of length 1 to 4, respectively, followed by a transparent segment of length 2. The space can be used repeatedly to enlarge the space between other line elements by 1, and can not occur as the first position in the string. The main difference of this syntax with the previous one is that it it shape-conserving. This means that all values in the dash list will be multiplied by the line width before display. This assures that . will always be displayed as a dot and - always as a dash regardless of the line width.

Some examples, for a line width of 2:



 -dash .     = -dash [2,4]
 -dash -     = -dash [6,4]
 -dash -.    = -dash [6,4,2,4]
 -dash -..   = -dash [6,4,2,4,2,4]
 -dash .   = -dash [2,8]
 -dash ,   = -dash [4,4]



On systems where only a limited set of dash patterns is available, the dash pattern will be displayed as the closest available dash pattern. For example, on Windows only the first 4 of the above examples are available. The last 2 examples will be displayed identically as the first one.

WIDGET METHODS

The <B>CanvasB> method creates a widget object. This object supports the <B>configureB> and <B>cgetB> methods described in Tk::options which can be used to enquire and modify the options described above. The widget also inherits all the methods provided by the generic Tk::Widget class.

The following additional methods are available for canvas widgets:
$canvas-><B>addtagB>(tag, searchSpec, ?arg, arg, ...?) For each item that meets the constraints specified by searchSpec and the args, add tag to the list of tags associated with the item if it isn’t already present on that list. It is possible that no items will satisfy the constraints given by searchSpec and args, in which case the method has no effect. This command returns an empty string as result. SearchSpec and arg’s may take any of the following forms:
<B>above B>tagOrId Selects the item just after (above) the one given by tagOrId in the display list. If tagOrId denotes more than one item, then the last (topmost) of these items in the display list is used.
<B>allB> Selects all the items in the canvas.
<B>below B>tagOrId Selects the item just before (below) the one given by tagOrId in the display list. If tagOrId denotes more than one item, then the first (lowest) of these items in the display list is used.
<B>closest B>x y ?halo? ?start? Selects the item closest to the point given by x and y. If more than one item is at the same closest distance (e.g. two items overlap the point), then the top-most of these items (the last one in the display list) is used. If halo is specified, then it must be a non-negative value. Any item closer than halo to the point is considered to overlap it. The start argument may be used to step circularly through all the closest items. If start is specified, it names an item using a tag or id (if by tag, it selects the first item in the display list with the given tag). Instead of selecting the topmost closest item, this form will select the topmost closest item that is below start in the display list; if no such item exists, then the selection behaves as if the start argument had not been specified.
<B>enclosedB> x1 y1 x2 y2 Selects all the items completely enclosed within the rectangular region given by x1, y1, x2, and y2. X1 must be no greater then x2 and y1 must be no greater than y2.
<B>overlappingB> x1 y1 x2 y2 Selects all the items that overlap or are enclosed within the rectangular region given by x1, y1, x2, and y2. X1 must be no greater then x2 and y1 must be no greater than y2.
<B>withtag B>tagOrId Selects all the items given by tagOrId.
$canvas-><B>bboxB>(tagOrId, ?tagOrId, tagOrId, ...?) Returns a list with four elements giving an approximate bounding box for all the items named by the tagOrId arguments. The list has the form ‘‘x1 y1 x2 y2’’ such that the drawn areas of all the named elements are within the region bounded by x1 on the left, x2 on the right, y1 on the top, and y2 on the bottom. The return value may overestimate the actual bounding box by a few pixels. If no items match any of the tagOrId arguments or if the matching items have empty bounding boxes (i.e. they have nothing to display) then an empty string is returned.
$canvas-><B>bindB>(tagOrId?, sequence? ?,callback?) This method associates callback with all the items given by tagOrId such that whenever the event sequence given by sequence occurs for one of the items the callback will be invoked. This method is similar to the <B>bindB> method except that it operates on items in a canvas rather than entire widgets. See Tk::bind for complete details on the syntax of sequence and the substitutions performed on callback before invoking it. If all arguments are specified then a new binding is created, replacing any existing binding for the same sequence and tagOrId (if the first character of command is ‘‘+’’ then command augments an existing binding rather than replacing it). In this case the return value is an empty string. If callback is omitted then the method returns the callback associated with tagOrId and sequence (an error occurs if there is no such binding). If both callback and sequence are omitted then the method returns a list of all the sequences for which bindings have been defined for tagOrId.

  The only events for which bindings may be specified are those related to the mouse and keyboard (such as <B>EnterB>, <B>LeaveB>, <B>ButtonPressB>, <B>MotionB>, and <B>KeyPressB>) or virtual events. The handling of events in canvases uses the current item defined in ITEM IDS AND TAGS above. <B>EnterB> and <B>LeaveB> events trigger for an item when it becomes the current item or ceases to be the current item; note that these events are different than <B>EnterB> and <B>LeaveB> events for windows. Mouse-related events are directed to the current item, if any. Keyboard-related events are directed to the focus item, if any (see the focus method below for more on this). If a virtual event is used in a binding, that binding can trigger only if the virtual event is defined by an underlying mouse-related or keyboard-related event.

It is possible for multiple bindings to match a particular event. This could occur, for example, if one binding is associated with the item’s id and another is associated with one of the item’s tags. When this occurs, all of the matching bindings are invoked. A binding associated with the <B>allB> tag is invoked first, followed by one binding for each of the item’s tags (in order), followed by a binding associated with the item’s id. If there are multiple matching bindings for a single tag, then only the most specific binding is invoked. A <B>continueB> in a callback terminates that subroutine, and a <B>breakB> method terminates that subroutine and skips any remaining callbacks for the event, just as for the <B>bindB> method.

If bindings have been created for a canvas window using the <B>CanvasBindB> method, then they are invoked in addition to bindings created for the canvas’s items using the <B>bindB> method. The bindings for items will be invoked before any of the bindings for the window as a whole.

$canvas-><B>canvasxB>(screenx?, gridspacing?) Given a window x-coordinate in the canvas screenx, this method returns the canvas x-coordinate that is displayed at that location. If gridspacing is specified, then the canvas coordinate is rounded to the nearest multiple of gridspacing units.
$canvas-><B>canvasyB>(screeny, ?gridspacing?) Given a window y-coordinate in the canvas screeny this method returns the canvas y-coordinate that is displayed at that location. If gridspacing is specified, then the canvas coordinate is rounded to the nearest multiple of gridspacing units.
$canvas-><B>coordsB>(tagOrId ?x0,y0 ...?) Query or modify the coordinates that define an item. If no coordinates are specified, this method returns a list whose elements are the coordinates of the item named by tagOrId. If coordinates are specified, then they replace the current coordinates for the named item. If tagOrId refers to multiple items, then the first one in the display list is used.
$canvas-><B>createB>(type, x, y, ?x, y, ...?, ?option, value, ...?) Create a new item in $canvas of type type. The exact format of the arguments after <B>typeB> depends on <B>typeB>, but usually they consist of the coordinates for one or more points, followed by specifications for zero or more item options. See the subsections on individual item types below for more on the syntax of this method. This method returns the id for the new item.
$canvas-><B>dcharsB>(tagOrId, first, ?last?) For each item given by tagOrId, delete the characters, or coordinates, in the range given by first and last, inclusive. If some of the items given by tagOrId don’t support Text items interpret first and last as indices to a character, line and polygon items interpret them indices to a coordinate (an x,y pair). within the item(s) as described in INDICES above. If last is omitted, it defaults to first. This method returns an empty string.
$canvas-><B>deleteB>(?tagOrId, tagOrId, ...?) Delete each of the items given by each tagOrId, and return an empty string.
$canvas-><B>dtagB>(tagOrId, ?tagToDelete?) For each of the items given by tagOrId, delete the tag given by tagToDelete from the list of those associated with the item. If an item doesn’t have the tag tagToDelete then the item is unaffected by the method. If tagToDelete is omitted then it defaults to tagOrId. This method returns an empty string.
$canvas-><B>findB>(searchCommand, ?arg, arg, ...?) This method returns a list consisting of all the items that meet the constraints specified by searchCommand and arg’s. SearchCommand and args have any of the forms accepted by the <B>addtagB> method. The items are returned in stacking order, with the lowest item first.
focus
$canvas-><B>focusB>(?tagOrId?) Set the keyboard focus for the canvas widget to the item given by tagOrId. If tagOrId refers to several items, then the focus is set to the first such item in the display list that supports the insertion cursor. If tagOrId doesn’t refer to any items, or if none of them support the insertion cursor, then the focus isn’t changed. If tagOrId is an empty string, then the focus item is reset so that no item has the focus. If tagOrId is not specified then the method returns the id for the item that currently has the focus, or an empty string if no item has the focus.

  Once the focus has been set to an item, the item will display the insertion cursor and all keyboard events will be directed to that item. The focus item within a canvas and the focus window on the screen (set with the <B>focusB> method) are totally independent: a given item doesn’t actually have the input focus unless (a) its canvas is the focus window and (b) the item is the focus item within the canvas. In most cases it is advisable to follow the <B>focusB> widget method with the <B>CanvasFocusB> method to set the focus window to the canvas (if it wasn’t there already).

$canvas-><B>gettagsB>(tagOrId) Return a list whose elements are the tags associated with the item given by tagOrId. If tagOrId refers to more than one item, then the tags are returned from the first such item in the display list. If tagOrId doesn’t refer to any items, or if the item contains no tags, then an empty string is returned.
$canvas-><B>icursorB>(tagOrId, index) Set the position of the insertion cursor for the item(s) given by tagOrId to just before the character whose position is given by index. If some or all of the items given by tagOrId don’t support an insertion cursor then this method has no effect on them. See INDICES above for a description of the legal forms for index. Note: the insertion cursor is only displayed in an item if that item currently has the keyboard focus (see the widget method <B>focusB>, below), but the cursor position may be set even when the item doesn’t have the focus. This method returns an empty string.
$canvas-><B>indexB>(tagOrId, index) This method returns a decimal string giving the numerical index within tagOrId corresponding to index. Index gives a textual description of the desired position as described in INDICES above. Text items interpret index as an index to a character, line and polygon items interpret it as an index to a coordinate (an x,y pair). The return value is guaranteed to lie between 0 and the number of characters, or coordinates, within the item, inclusive. If tagOrId refers to multiple items, then the index is processed in the first of these items that supports indexing operations (in display list order).
$canvas-><B>insertB>(tagOrId, beforeThis, string) For each of the items given by tagOrId, if the item supports text or coordinate, insertion then string is inserted into the item’s text just before the character, or coordinate, whose index is beforeThis. Text items interpret beforethis as an index to a character, line and polygon items interpret it as an index to a coordinate (an x,y pair). For lines and polygons the string must be a valid coordinate sequence. See INDICES above for information about the forms allowed for beforeThis. This method returns an empty string.
$canvas-><B>itemcgetB>(tagOrId, option) Returns the current value of the configuration option for the item given by tagOrId whose name is option. This method is similar to the cget method except that it applies to a particular item rather than the widget as a whole. Option may have any of the values accepted by the <B>createB> method when the item was created. If tagOrId is a tag that refers to more than one item, the first (lowest) such item is used.
$canvas-><B>itemconfigureB>(tagOrId, ?option?, ?value?, ?option, value, ...?) This method is similar to the configure method except that it modifies item-specific options for the items given by tagOrId instead of modifying options for the overall canvas widget. If no option is specified, returns a list describing all of the available options for the first item given by tagOrId (see Tk::options for information on the format of this list). If option is specified with no value, then the method returns a list describing the one named option (this list will be identical to the corresponding sublist of the value returned if no option is specified). If one or more option-value pairs are specified, then the method modifies the given widget option(s) to have the given value(s) in each of the items given by tagOrId; in this case the method returns an empty string. The options and values are the same as those permissible in the <B>createB> method when the item(s) were created; see the sections describing individual item types below for details on the legal options.
$canvas-><B>lowerB>(tagOrId, ?belowThis?) Move all of the items given by tagOrId to a new position in the display list just before the item given by belowThis. If tagOrId refers to more than one item then all are moved but the relative order of the moved items will not be changed. BelowThis is a tag or id; if it refers to more than one item then the first (lowest) of these items in the display list is used as the destination location for the moved items. Note: this method has no effect on window items. Window items always obscure other item types, and the stacking order of window items is determined by the <B>raiseB> and <B>lowerB> methods of the widget, not the <B>raiseB> and <B>lowerB> methods for canvases. This method returns an empty string.
$canvas-><B>moveB>(tagOrId, xAmount, yAmount) Move each of the items given by tagOrId in the canvas coordinate space by adding xAmount to the x-coordinate of each point associated with the item and yAmount to the y-coordinate of each point associated with the item. This method returns an empty string.
$canvas-><B>postscriptB>(?option, value, option, value, ...?) Generate a Postscript representation for part or all of the canvas. If the <B>-fileB> option is specified then the Postscript is written to a file and an empty string is returned; otherwise the Postscript is returned as the result of the method. If the interpreter that owns the canvas is marked as safe, the operation will fail because safe interpreters are not allowed to write files. If the <B>-channelB> option is specified, the argument denotes the name of a channel already opened for writing. The Postscript is written to that channel, and the channel is left open for further writing at the end of the operation. The Postscript is created in Encapsulated Postscript form using version 3.0 of the Document Structuring Conventions. Note: by default Postscript is only generated for information that appears in the canvas’s window on the screen. If the canvas is freshly created it may still have its initial size of 1x1 pixel so nothing will appear in the Postscript. To get around this problem either invoke the <B>updateB> method to wait for the canvas window to reach its final size, or else use the <B>-widthB> and <B>-heightB> options to specify the area of the canvas to print. The option-value argument pairs provide additional information to control the generation of Postscript. The following options are supported:
<B>-colormapB> => hashRef HashRef must be a reference to a hash variable or an anonymous hash that specifies a color mapping to use in the Postscript. Each value of the hash must consist of Postscript code to set a particular color value (e.g. ‘‘<B>1.0 1.0 0.0 setrgbcolorB>’’). When outputting color information in the Postscript, Tk checks to see if there is a key in the hash with the same name as the color. If so, Tk uses the value of the element as the Postscript method to set the color. If this option hasn’t been specified, or if there isn’t a key in hashRef for a given color, then Tk uses the red, green, and blue intensities from the X color.
<B>-colormodeB> => mode Specifies how to output color information. Mode must be either <B>colorB> (for full color output), <B>grayB> (convert all colors to their gray-scale equivalents) or <B>monoB> (convert all colors to black or white).
<B>-fileB> => fileName Specifies the name of the file in which to write the Postscript. If this option isn’t specified then the Postscript is returned as the result of the method instead of being written to a file.
<B>-fontmapB> => hashRef HashRef must be a reference to a hash variable or an anonymous hash that specifies a font mapping to use in the Postscript. Each value of the hash must consist of an array reference with two elements, which are the name and point size of a Postscript font. When outputting Postscript commands for a particular font, Tk checks to see if hashRef contains a value with the same name as the font. If there is such an element, then the font information contained in that element is used in the Postscript. Otherwise Tk attempts to guess what Postscript font to use. Tk’s guesses generally only work for well-known fonts such as Times and Helvetica and Courier, and only if the X font name does not omit any dashes up through the point size. For example, <B>-*-Courier-Bold-R-Normal--*-120-*B> will work but <B>*Courier-Bold-R-Normal*120*B> will not; Tk needs the dashes to parse the font name).
<B>-heightB> => size Specifies the height of the area of the canvas to print. Defaults to the height of the canvas window.
<B>-pageanchorB> => anchor Specifies which point of the printed area of the canvas should appear over the positioning point on the page (which is given by the <B>-pagexB> and <B>-pageyB> options). For example, <B>-pageanchorB>=><B>nB> means that the top center of the area of the canvas being printed (as it appears in the canvas window) should be over the positioning point. Defaults to <B>centerB>.
<B>-pageheightB> => size Specifies that the Postscript should be scaled in both x and y so that the printed area is size high on the Postscript page. Size consists of a floating-point number followed by <B>cB> for centimeters, <B>iB> for inches, <B>mB> for millimeters, or <B>pB> or nothing for printer’s points (1/72 inch). Defaults to the height of the printed area on the screen. If both <B>-pageheightB> and <B>-pagewidthB> are specified then the scale factor from <B>-pagewidthB> is used (non-uniform scaling is not implemented).
<B>-pagewidthB> => size Specifies that the Postscript should be scaled in both x and y so that the printed area is size wide on the Postscript page. Size has the same form as for <B>-pageheightB>. Defaults to the width of the printed area on the screen. If both <B>-pageheightB> and <B>-pagewidthB> are specified then the scale factor from <B>-pagewidthB> is used (non-uniform scaling is not implemented).
<B>-pagexB> => position Position gives the x-coordinate of the positioning point on the Postscript page, using any of the forms allowed for <B>-pageheightB>. Used in conjunction with the <B>-pageyB> and <B>-pageanchorB> options to determine where the printed area appears on the Postscript page. Defaults to the center of the page.
<B>-pageyB> => position Position gives the y-coordinate of the positioning point on the Postscript page, using any of the forms allowed for <B>-pageheightB>. Used in conjunction with the <B>-pagexB> and <B>-pageanchorB> options to determine where the printed area appears on the Postscript page. Defaults to the center of the page.
<B>-rotateB> => boolean Boolean specifies whether the printed area is to be rotated 90 degrees. In non-rotated output the x-axis of the printed area runs along the short dimension of the page (‘‘portrait’’ orientation); in rotated output the x-axis runs along the long dimension of the page (‘‘landscape’’ orientation). Defaults to non-rotated.
<B>-widthB> => size Specifies the width of the area of the canvas to print. Defaults to the width of the canvas window.
<B>-xB> => position Specifies the x-coordinate of the left edge of the area of the canvas that is to be printed, in canvas coordinates, not window coordinates. Defaults to the coordinate of the left edge of the window.
<B>-yB> => position Specifies the y-coordinate of the top edge of the area of the canvas that is to be printed, in canvas coordinates, not window coordinates. Defaults to the coordinate of the top edge of the window.
$canvas-><B>raiseB>(tagOrId, ?aboveThis?) Move all of the items given by tagOrId to a new position in the display list just after the item given by aboveThis. If tagOrId refers to more than one item then all are moved but the relative order of the moved items will not be changed. AboveThis is a tag or id; if it refers to more than one item then the last (topmost) of these items in the display list is used as the destination location for the moved items. Note: this method has no effect on window items. Window items always obscure other item types, and the stacking order of window items is determined by the <B>raiseB> and <B>lowerB> widget commands, not the <B>raiseB> and <B>lowerB> methods for canvases. This method returns an empty string.
$canvas-><B>scaleB>(tagOrId, xOrigin, yOrigin, xScale, yScale) Rescale all of the items given by tagOrId in canvas coordinate space. XOrigin and yOrigin identify the origin for the scaling operation and xScale and yScale identify the scale factors for x- and y-coordinates, respectively (a scale factor of 1.0 implies no change to that coordinate). For each of the points defining each item, the x-coordinate is adjusted to change the distance from xOrigin by a factor of xScale. Similarly, each y-coordinate is adjusted to change the distance from yOrigin by a factor of yScale. This method returns an empty string.
$canvas-><B>scanB>(option, args) This method is used to implement scanning on canvases. It has two forms, depending on option:
$canvas-><B>scanMarkB>(x, y) Records x and y and the canvas’s current view; used in conjunction with later <B>scanDragtoB> method. Typically this method is associated with a mouse button press in the widget and x and y are the coordinates of the mouse. It returns an empty string.
$canvas-><B>scanDragtoB>(x, y, ?gain?.) This method computes the difference between its x and y arguments (which are typically mouse coordinates) and the x and y arguments to the last <B>scanMarkB> method for the widget. It then adjusts the view by 10 times the difference in coordinates. This method is typically associated It then adjusts the view by gain times the difference in coordinates, where gain defaults to 10. This command is typically associated with mouse motion events in the widget, to produce the effect of dragging the canvas at high speed through its window. The return value is an empty string.
$canvas-><B>selectB>(option, ?tagOrId, arg?) Manipulates the selection in one of several ways, depending on option. The method may take any of the forms described below. In all of the descriptions below, tagOrId must refer to an item that supports indexing and selection; if it refers to multiple items then the first of these that supports indexing and the selection is used. Index gives a textual description of a position within tagOrId, as described in INDICES above.
$canvas-><B>selectAdjustB>(tagOrId, index) Locate the end of the selection in tagOrId nearest to the character given by index, and adjust that end of the selection to be at index (i.e. including but not going beyond index). The other end of the selection is made the anchor point for future <B>selectToB> method calls. If the selection isn’t currently in tagOrId then this method behaves the same as the <B>selectToB> widget method. Returns an empty string.
$canvas-><B>selectClearB> Clear the selection if it is in this widget. If the selection isn’t in this widget then the method has no effect. Returns an empty string.
$canvas-><B>selectFromB>(tagOrId, index) Set the selection anchor point for the widget to be just before the character given by index in the item given by tagOrId. This method doesn’t change the selection; it just sets the fixed end of the selection for future <B>selectToB> method calls. Returns an empty string.
$canvas-><B>selectItemB> Returns the id of the selected item, if the selection is in an item in this canvas. If the selection is not in this canvas then an empty string is returned.
$canvas-><B>selectToB>(tagOrId, index) Set the selection to consist of those characters of tagOrId between the selection anchor point and index. The new selection will include the character given by index; it will include the character given by the anchor point only if index is greater than or equal to the anchor point. The anchor point is determined by the most recent <B>selectAdjustB> or <B>selectFromB> method calls for this widget. If the selection anchor point for the widget isn’t currently in tagOrId, then it is set to the same character given by index. Returns an empty string.
$canvas-><B>typeB>(tagOrId) Returns the type of the item given by tagOrId, such as <B>rectangleB> or <B>textB>. If tagOrId refers to more than one item, then the type of the first item in the display list is returned. If tagOrId doesn’t refer to any items at all then an empty string is returned.
$canvas-><B>xviewB>(?args?) This method is used to query and change the horizontal position of the information displayed in the canvas’s window. It can take any of the following forms:
$canvas-><B>xviewB> Returns a list containing two elements. Each element is a real fraction between 0 and 1; together they describe the horizontal span that is visible in the window. For example, if the first element is .2 and the second element is .6, 20% of the canvas’s area (as defined by the <B>-scrollregionB> option) is off-screen to the left, the middle 40% is visible in the window, and 40% of the canvas is off-screen to the right. These are the same values passed to scrollbars via the <B>-xscrollcommandB> option.
$canvas-><B>xviewMovetoB>(fraction) Adjusts the view in the window so that fraction of the total width of the canvas is off-screen to the left. Fraction must be a fraction between 0 and 1.
$canvas-><B>xviewScrollB>(number, what) This method shifts the view in the window left or right according to number and what. Number must be an integer. What must be either <B>unitsB> or <B>pagesB> or an abbreviation of one of these. If what is <B>unitsB>, the view adjusts left or right in units of the <B>xScrollIncrementB> option, if it is greater than zero, or in units of one-tenth the window’s width otherwise. If what is <B>pagesB> then the view adjusts in units of nine-tenths the window’s width. If number is negative then information farther to the left becomes visible; if it is positive then information farther to the right becomes visible.
$canvas-><B>yviewB>(?args?) This method is used to query and change the vertical position of the information displayed in the canvas’s window. It can take any of the following forms:
$canvas-><B>yviewB> Returns a list containing two elements. Each element is a real fraction between 0 and 1; together they describe the vertical span that is visible in the window. For example, if the first element is .6 and the second element is 1.0, the lowest 40% of the canvas’s area (as defined by the <B>-scrollregionB> option) is visible in the window. These are the same values passed to scrollbars via the <B>-yscrollcommandB> option.
$canvas-><B>yviewMovetoB>(fraction) Adjusts the view in the window so that fraction of the canvas’s area is off-screen to the top. Fraction is a fraction between 0 and 1.
$canvas-><B>yviewScrollB>(number, what) This method adjusts the view in the window up or down according to number and what. Number must be an integer. What must be either <B>unitsB> or <B>pagesB>. If what is <B>unitsB>, the view adjusts up or down in units of the <B>yScrollIncrementB> option, if it is greater than zero, or in units of one-tenth the window’s height otherwise. If what is <B>pagesB> then the view adjusts in units of nine-tenths the window’s height. If number is negative then higher information becomes visible; if it is positive then lower information becomes visible.

OVERVIEW OF ITEM TYPES

The sections below describe the various types of items supported by canvas widgets. Each item type is characterized by two things: first, the form of the <B>createB> method used to create instances of the type; and second, a set of configuration options for items of that type, which may be used in the <B>createB> and <B>itemconfigureB> methods. Most items don’t support indexing or selection or the methods related to them, such as <B>indexB> and <B>insertB>. Where items do support these facilities, it is noted explicitly in the descriptions below. At present, text, line and polygon items provide this support. For lines and polygons the indexing facility is used to manipulate the coordinates of the item.

ARC ITEMS

Items of type <B>arcB> appear on the display as arc-shaped regions. An arc is a section of an oval delimited by two angles (specified by the <B>-startB> and <B>-extentB> options) and displayed in one of several ways (specified by the <B>-styleB> option). Arcs are created with methods of the following form:



 $canvas->createArc(x1, y1, x2, y2, ?option, value, option, value, ...?)



The arguments x1, y1, x2, and y2 give the coordinates of two diagonally opposite corners of a rectangular region enclosing the oval that defines the arc. After the coordinates there may be any number of option-value pairs, each of which sets one of the configuration options for the item. These same option-value pairs may be used in <B>itemconfigureB> methods to change the item’s configuration. The following options are supported for arcs:
<B>-dashB> => pattern
<B>-activedashB> => pattern
<B>-disableddashB> => pattern This option specifies dash patterns for the normal state, the active state, and the disabled state of an arc item. pattern may have any of the forms accepted by <B>Tk_GetDashB>. If the dash options are omitted then the default is a solid outline.
<B>-dashoffsetB> => offset The starting offset into the pattern provided by the <B>-dashB> option. <B>-dashoffsetB> is ignored if there is no <B>-dashB> pattern.
<B>-extentB> => degrees Specifies the size of the angular range occupied by the arc. The arc’s range extends for degrees degrees counter-clockwise from the starting angle given by the <B>-startB> option. Degrees may be negative. If it is greater than 360 or less than -360, then degrees modulo 360 is used as the extent.
<B>-fillB> => color
<B>-activefillB> => color
<B>-disabledfillB> => color Specifies the color to be used to fill the arc region in its normal, active, and disabled states, Color may have any of the forms accepted by <B>Tk_GetColorB>. If color is an empty string (the default), then then the arc will not be filled.
<B>-outlineB> => color
<B>-activeoutlineB> => color
<B>-disabledoutlineB> => color This option specifies the color that should be used to draw the outline of the arc in its normal, active and disabled states. Color may have any of the forms accepted by <B>Tk_GetColorB>. This option defaults to <B>blackB>. If color is specified as undef then no outline is drawn for the arc.
<B>-outlinestippleB> => bitmap
<B>-activeoutlinestippleB> => bitmap
<B>-disabledoutlinestippleB> => bitmap This option specifies stipple patterns that should be used to draw the outline of the arc in its normal, active and disabled states. Indicates that the outline for the arc should be drawn with a stipple pattern; bitmap specifies the stipple pattern to use, in any of the forms accepted by <B>Tk_GetBitmapB>. If the <B>-outlineB> option hasn’t been specified then this option has no effect. If bitmap is an empty string (the default), then the outline is drawn in a solid fashion.
<B>-startB> => degrees Specifies the beginning of the angular range occupied by the arc. Degrees is given in units of degrees measured counter-clockwise from the 3-o’clock position; it may be either positive or negative.
<B>-stateB> => state Modifies the state of the arc item where state may be set to one of: normal, disabled, hidden or ". If set to empty, the state of the canvas itself is used. An arc item may also be in the active" state if the mouse is currently over it. Many options can take separate specifications in normal, active and disabled states such that the appearance of the item can be different in each state.
<B>-stippleB> => bitmap
<B>-activestippleB> => bitmap
<B>-disabledstippleB> => bitmap This option specifies stipple patterns that should be used to fill the the arc in its normal, active and disabled states. bitmap specifies the stipple pattern to use, in any of the forms accepted by <B>Tk_GetBitmapB>. If the <B>-fillB> option hasn’t been specified then this option has no effect. If bitmap is an empty string (the default), then filling is done in a solid fashion.
<B>-styleB> => type Specifies how to draw the arc. If type is <B>piesliceB> (the default) then the arc’s region is defined by a section of the oval’s perimeter plus two line segments, one between the center of the oval and each end of the perimeter section. If type is <B>chordB> then the arc’s region is defined by a section of the oval’s perimeter plus a single line segment connecting the two end points of the perimeter section. If type is <B>arcB> then the arc’s region consists of a section of the perimeter alone. In this last case the <B>-fillB> option is ignored.
<B>-tagsB> => tagList Specifies a set of tags to apply to the item. TagList consists of a list of tag names, which replace any existing tags for the item. TagList may be an empty list.
<B>-updatecommandB> => command Specifies a callback that is to be executed every time the arc item is updated on the screen.
<B>-widthB> => outlineWidth
<B>-activewidthB> => outlineWidth
<B>-disabledwidthB> => outlineWidth Specifies the width of the outline to be drawn around the arc’s region, in its normal, active and disabled states. outlineWidth may be in any of the forms described in the COORDINATES section above. If the <B>-outlineB> option has been specified as undef then this option has no effect. Wide outlines will be drawn centered on the edges of the arc’s region. This option defaults to 1.0.

BITMAP ITEMS

Items of type <B>bitmapB> appear on the display as images with two colors, foreground and background. Bitmaps are created with methods of the following form:



 $canvas->createBitmap(x, y, ?option, value, option, value, ...?)



The arguments x and y specify the coordinates of a point used to position the bitmap on the display (see the <B>-anchorB> option below for more information on how bitmaps are displayed). After the coordinates there may be any number of option-value pairs, each of which sets one of the configuration options for the item. These same option-value pairs may be used in <B>itemconfigureB> methods to change the item’s configuration. The following options are supported for bitmaps:
<B>-anchorB> => anchorPos AnchorPos tells how to position the bitmap relative to the positioning point for the item; it may have any of the forms accepted by <B>Tk_GetAnchorB>. For example, if anchorPos is <B>centerB> then the bitmap is centered on the point; if anchorPos is <B>nB> then the bitmap will be drawn so that its top center point is at the positioning point. This option defaults to <B>centerB>.
<B>-backgroundB> => color
<B>-activebackgroundB> => color
<B>-disabledbackgroundB> => color Specifies the color to use for each of the bitmap’s ’0’ valued pixels in its normal, active and disabled states. Color may have any of the forms accepted by <B>Tk_GetColorB>. If this option isn’t specified, or if it is specified as undef, then nothing is displayed where the bitmap pixels are 0; this produces a transparent effect.
<B>-bitmapB> => bitmap
<B>-activebitmapB> => bitmap
<B>-disabledbitmapB> => bitmap Specifies the bitmaps to display in the item in its normal, active and disabled states. All bitmaps must have the same width and height. Bitmap may have any of the forms accepted by <B>Tk_GetBitmapB>.
<B>-foregroundB> => color
<B>-activeforegroundB> => color
<B>-disabledforegroundB> => color Specifies the color to use for each of the bitmap’s ’1’ valued pixels in its normal, active and disabled states. Color may have any of the forms accepted by <B>Tk_GetColorB> and defaults to <B>blackB>.
<B>-stateB> => state Modifies the state of the bitmap item where state may be set to one of: normal, disabled, or hidden. An bitmap item may also be in the active state if the mouse is currently over it. Many options can take separate specifications in normal, active and disabled states such that the appearance of the item can be different in each state.
<B>-tagsB> => tagList Specifies a set of tags to apply to the item. TagList consists of a list of tag names, which replace any existing tags for the item. TagList may be an empty list.
<B>-updatecommandB> => command Specifies a callback that is to be executed every time the bitmap item is updated on the screen.

GRID ITEMS

Items of type <B>gridB> are intended for producing a visual reference for interpreting other items. They can be drawn as either lines (with dash style) or as rectangular dots at each grid point.

Items of type <B>gridB> are unlike other items they always cover the whole of the canvas, but are never enclosed by nor overlap any area and are not near any point. That is they are intended to be always visible but not pickable, as such they do support the active state. They are like other items in that: multiple grids are permitted, they can be raised and lowered relative to other items, they can be moved and scaled. As yet grids do not appear in PostScript output.

Grids have outline like configure options. Grids are created with methods of the following form:



 $canvas->createGrid(x1, y1, x2, y2, ?option, value, option, value, ...?)



The arguments x1, y1 give the origin of the grid. x2, and y2 give the coordinates of the next grid point in their respective directions. After the coordinates there may be any number of option-value pairs, each of which sets one of the configuration options for the item. These same option-value pairs may be used in <B>itemconfigureB> methods to change the item’s configuration.

The following options are supported for grids:
<B>-linesB> => boolean If <B>-linesB> is set to a true value then lines are drawn for both X and Y grids in the style determined by <B>-dashB>. Otherwise retangular dots are drawn at each grid point.
<B>-dashB> => pattern
<B>-disableddashB> => pattern This option specifies dash patterns for the normal state, and the disabled state of a grid item. pattern may have any of the forms accepted by <B>Tk_GetDashB>. If the dash options are omitted then the default is a solid outline.
<B>-dashoffsetB> => offset The starting offset into the pattern provided by the <B>-dashB> option. <B>-dashoffsetB> is ignored if there is no <B>-dashB> pattern.
<B>-colorB> => color
<B>-disabledcolorB> => color This option specifies the color that should be used to draw the outline of the grid in its normal and disabled states. Color may have any of the forms accepted by <B>Tk_GetColorB>. This option defaults to <B>blackB>. If color is undef then no grid will be drawn.
<B>-stippleB> => bitmap
<B>-disabledstippleB> => bitmap This option specifies stipple patterns that should be used to draw the outline of the rectangle in its normal and disabled states. bitmap specifies the stipple pattern to use, in any of the forms accepted by <B>Tk_GetBitmapB>. If bitmap is an empty string (the default), then the outline is drawn in a solid fashion.
<B>-stateB> => state Modifies the state of the rectangle item where state may be set to one of: normal, disabled, or hidden. Many options can take separate specifications in normal and disabled states such that the appearance of the item can be different in each state.
<B>-tagsB> => tagList Specifies a set of tags to apply to the item. TagList consists of a list of tag names, which replace any existing tags for the item. TagList may be an empty list.
<B>-updatecommandB> => command Specifies a callback that is to be executed every time the grid item is updated on the screen.
<B>-widthB> => outlineWidth
<B>-disabledwidthB> => outlineWidth Specifies the width of the lines drawn by the grid or the size (in both X and Y) of the dots, in its normal and disabled states. This option defaults to 1.0.

IMAGE ITEMS

Items of type <B>imageB> are used to display images on a canvas. Images are created with methods of the following form:



 $canvas->createImage(x, y, ?option, value, option, value, ...?)



The arguments x and y specify the coordinates of a point used to position the image on the display (see the <B>-anchorB> option below for more information). After the coordinates there may be any number of option-value pairs, each of which sets one of the configuration options for the item. These same option-value pairs may be used in <B>itemconfigureB> methods to change the item’s configuration. The following options are supported for images:
<B>-anchorB> => anchorPos AnchorPos tells how to position the image relative to the positioning point for the item; it may have any of the forms accepted by <B>Tk_GetAnchorB>. For example, if anchorPos is <B>centerB> then the image is centered on the point; if anchorPos is <B>nB> then the image will be drawn so that its top center point is at the positioning point. This option defaults to <B>centerB>.
<B>-imageB> => name
<B>-activeimageB> => name
<B>-disabledimageB> => name Specifies the name of the images to display in the item in is normal, active and disabled states. This image must have been created previously, see Tk::Image.
<B>-stateB> => state Modifies the state of the image item where state may be set to one of: normal, disabled, or hidden. An image item may also be in the active state if the mouse is currently over it. Many options can take separate specifications in normal, active and disabled states such that the appearance of the item can be different in each state.
<B>-tagsB> => tagList Specifies a set of tags to apply to the item. TagList consists of a list of tag names, which replace any existing tags for the item; it may be an empty list.
<B>-updatecommandB> => command Specifies a callback that is to be executed every time the image item is updated on the screen.

LINE ITEMS

Items of type <B>lineB> appear on the display as one or more connected line segments or curves. Line items support coordinate indexing operations using the canvas methods: <B>dchars, index, insert.B> Lines are created with methods of the following form:



 $canvas->createLine(x1, y1..., xn, yn, ?option, value, option, value, ...?)



The arguments x1 through yn give the coordinates for a series of two or more points that describe a series of connected line segments. After the coordinates there may be any number of option-value pairs, each of which sets one of the configuration options for the item. These same option-value pairs may be used in <B>itemconfigureB> methods to change the item’s configuration. The following options are supported for lines:
<B>-arrowB> => where Indicates whether or not arrowheads are to be drawn at one or both ends of the line. Where must have one of the values <B>noneB> (for no arrowheads), <B>firstB> (for an arrowhead at the first point of the line), <B>lastB> (for an arrowhead at the last point of the line), or <B>bothB> (for arrowheads at both ends). This option defaults to <B>noneB>.
<B>-arrowshapeB> => shape This option indicates how to draw arrowheads. The shape argument must be a list with three elements, each specifying a distance in any of the forms described in the COORDINATES section above. The first element of the list gives the distance along the line from the neck of the arrowhead to its tip. The second element gives the distance along the line from the trailing points of the arrowhead to the tip, and the third element gives the distance from the outside edge of the line to the trailing points. If this option isn’t specified then Tk picks a ‘‘reasonable’’ shape.
<B>-capstyleB> => style Specifies the ways in which caps are to be drawn at the endpoints of the line. Style may have any of the forms accepted by <B>Tk_GetCapStyleB> (<B>buttB>, <B>projectingB>, or <B>roundB>). If this option isn’t specified then it defaults to <B>buttB>. Where arrowheads are drawn the cap style is ignored.
<B>-dashB> => pattern
<B>-activedashB> => pattern
<B>-disableddashB> => pattern This option specifies dash patterns for the normal state, the active state, and the disabled state of a line item. pattern may have any of the forms accepted by <B>Tk_GetDashB>. If the dash options are omitted then the default is a solid outline.
<B>-dashoffsetB> => offset The starting offset into the pattern provided by the <B>-dashB> option. <B>-dashoffsetB> is ignored if there is no <B>-dashB> pattern.
<B>-fillB> => color
<B>-activefillB> => color
<B>-disabledfillB> => color Specifies the color to be used to fill the line in its normal, active, and disabled states. Color may have any of the forms acceptable to <B>Tk_GetColorB>. It may also be undef, in which case the line will be transparent. This option defaults to <B>blackB>.
<B>-joinstyleB> => style Specifies the ways in which joints are to be drawn at the vertices of the line. Style may have any of the forms accepted by <B>Tk_GetCapStyleB> (<B>bevelB>, <B>miterB>, or <B>roundB>). If this option isn’t specified then it defaults to <B>miterB>. If the line only contains two points then this option is irrelevant.
<B>-smoothB> => boolean Boolean must have one of the forms accepted by <B>Tk_GetBooleanB>. It indicates whether or not the line should be drawn as a curve. If so, the line is rendered as a set of parabolic splines: one spline is drawn for the first and second line segments, one for the second and third, and so on. Straight-line segments can be generated within a curve by duplicating the end-points of the desired line segment.
<B>-splinestepsB> => number Specifies the degree of smoothness desired for curves: each spline will be approximated with number line segments. This option is ignored unless the <B>-smoothB> option is true.
<B>-stateB> => state Modifies the state of the line item where state may be set to one of: normal, disabled, or hidden. A line item may also be in the active state if the mouse is currently over it. Many options can take separate specifications in normal, active and disabled states such that the appearance of the item can be different in each state.
<B>-stippleB> => bitmap
<B>-activestippleB> => bitmap
<B>-disabledstippleB> => bitmap This option specifies stipple patterns that should be used to fill the the line in its normal, active and disabled states. bitmap specifies the stipple pattern to use, in any of the forms accepted by <B>Tk_GetBitmapB>. If bitmap is an empty string (the default), then filling is done in a solid fashion.
<B>-tagsB> => tagList Specifies a set of tags to apply to the item. TagList consists of a list of tag names, which replace any existing tags for the item. TagList may be an empty list.
<B>-updatecommandB> => command Specifies a callback that is to be executed every time the line item is updated on the screen.
<B>-widthB> => lineWidth
<B>-activewidthB> => lineWidth
<B>-disabledwidthB> => lineWidth Specifies the width of the line in its normal, active and disabled states. lineWidth may be in any of the forms described in the COORDINATES section above.

Wide lines will be drawn centered on the path specified by the points. If this option isn’t specified then it defaults to 1.0.

OVAL ITEMS

Items of type <B>ovalB> appear as circular or oval regions on the display. Each oval may have an outline, a fill, or both. Ovals are created with methods of the following form:



 $canvas->createOval(x1, y1, x2, y2, ?option, value, option, value, ...?)



The arguments x1, y1, x2, and y2 give the coordinates of two diagonally opposite corners of a rectangular region enclosing the oval. The oval will include the top and left edges of the rectangle not the lower or right edges. If the region is square then the resulting oval is circular; otherwise it is elongated in shape. After the coordinates there may be any number of option-value pairs, each of which sets one of the configuration options for the item. These same option-value pairs may be used in <B>itemconfigureB> methods to change the item’s configuration. The following options are supported for ovals:
<B>-dashB> => pattern
<B>-activedashB> => pattern
<B>-disableddashB> => pattern This option specifies dash patterns for the normal state, the active state, and the disabled state of an oval item. pattern may have any of the forms accepted by <B>Tk_GetDashB>. If the dash options are omitted then the default is a solid outline.
<B>-dashoffsetB> => offset The starting offset into the pattern provided by the <B>-dashB> option. <B>-dashoffsetB> is ignored if there is no <B>-dashB> pattern.
<B>-fillB> => color
<B>-activefillB> => color
<B>-disabledfillB> => color Specifies the color to be used to fill the oval in its normal, active, and disabled states. Color may have any of the forms accepted by <B>Tk_GetColorB>. If color is undef (the default), then then the oval will not be filled.
<B>-outlineB> => color
<B>-activeoutlineB> => color
<B>-disabledoutlineB> => color This option specifies the color that should be used to draw the outline of the oval in its normal, active and disabled states. Color may have any of the forms accepted by <B>Tk_GetColorB>. This option defaults to <B>blackB>. If color is undef then no outline will be drawn for the oval.
<B>-outlinestippleB> => bitmap
<B>-activeoutlinestippleB> => bitmap
<B>-disabledoutlinestippleB> => bitmap This option specifies stipple patterns that should be used to draw the outline of the oval in its normal, active and disabled states. bitmap specifies the stipple pattern to use, in any of the forms accepted by <B>Tk_GetBitmapB>. If the <B>-outlineB> option hasn’t been specified then this option has no effect. If bitmap is an empty string (the default), then the outline is drawn in a solid fashion.
<B>-stateB> => state Modifies the state of the oval item where state may be set to one of: normal, disabled, or hidden. An oval item may also be in the active state if the mouse is currently over it. Many options can take separate specifications in normal, active and disabled states such that the appearance of the item can be different in each state.
<B>-stippleB> => bitmap
<B>-activestippleB> => bitmap
<B>-disabledstippleB> => bitmap This option specifies stipple patterns that should be used to fill the the oval in its normal, active and disabled states. bitmap specifies the stipple pattern to use, in any of the forms accepted by <B>Tk_GetBitmapB>. If the <B>-fillB> option hasn’t been specified then this option has no effect. If bitmap is an empty string (the default), then filling is done in a solid fashion.
<B>-tagsB> => tagList Specifies a set of tags to apply to the item. TagList consists of a list of tag names, which replace any existing tags for the item. TagList may be an empty list.
<B>-updatecommandB> => command Specifies a callback that is to be executed every time the oval item is updated on the screen.
<B>-widthB> => outlineWidth
<B>-activewidthB> => outlineWidth
<B>-disabledwidthB> => outlineWidth Specifies the width of the outline to be drawn around the oval, in its normal, active and disabled states. outlineWidth specifies the width of the outline to be drawn around the oval, in any of the forms described in the COORDINATES section above.

If the <B>-outlineB> option hasn’t been specified then this option has no effect. Wide outlines are drawn centered on the oval path defined by x1, y1, x2, and y2. This option defaults to 1.0.

POLYGON ITEMS

Items of type <B>polygonB> appear as polygonal or curved filled regions on the display. Polygon items support coordinate indexing operations using the canvas methods: <B>dchars, index, insert.B> Polygons are created with methods of the following form:



 $canvas->createPolygon(x1, y1, ..., xn, yn, ?option, value, option, value, ...?)



The arguments x1 through yn specify the coordinates for three or more points that define a closed polygon. The first and last points may be the same; whether they are or not, Tk will draw the polygon as a closed polygon. After the coordinates there may be any number of option-value pairs, each of which sets one of the configuration options for the item. These same option-value pairs may be used in <B>itemconfigureB> methods to change the item’s configuration. The following options are supported for polygons:
<B>-dashB> => pattern
<B>-activedashB> => pattern
<B>-disableddashB> => pattern This option specifies dash patterns for the normal state, the active state, and the disabled state of an polygon item. pattern may have any of the forms accepted by <B>Tk_GetDashB>. If the dash options are omitted then the default is a solid outline.
<B>-dashoffsetB> => offset The starting offset into the pattern provided by the <B>-dashB> option. <B>-dashoffsetB> is ignored if there is no <B>-dashB> pattern.
<B>-fillB> => color
<B>-activefillB> => color
<B>-disabledfillB> => color Specifies the color to be used to fill the polygon in its normal, active, and disabled states. Color may have any of the forms acceptable to <B>Tk_GetColorB>. If color is undef then the polygon will be transparent. This option defaults to <B>blackB>.
<B>-joinstyleB> => style Specifies the ways in which joints are to be drawn at the vertices of the outline. Style may have any of the forms accepted by <B>Tk_GetCapStyleB> (<B>bevelB>, <B>miterB>, or <B>roundB>). If this option isn’t specified then it defaults to <B>miterB>.
<B>-outlineB> => color
<B>-activeoutlineB> => color
<B>-disabledoutlineB> => color This option specifies the color that should be used to draw the outline of the polygon in its normal, active and disabled states. Color may have any of the forms accepted by <B>Tk_GetColorB>. If color is undef then no outline will be drawn for the polygon. This option defaults to undef (no outline).
<B>-outlinestippleB> => bitmap
<B>-activeoutlinestippleB> => bitmap
<B>-disabledoutlinestippleB> => bitmap This option specifies stipple patterns that should be used to draw the outline of the polygon in its normal, active and disabled states. bitmap specifies the stipple pattern to use, in any of the forms accepted by <B>Tk_GetBitmapB>. If the <B>-outlineB> option hasn’t been specified then this option has no effect. If bitmap is an empty string (the default), then the outline is drawn in a solid fashion.
<B>-smoothB> => boolean Boolean must have one of the forms accepted by <B>Tk_GetBooleanB> It indicates whether or not the polygon should be drawn with a curved perimeter. If so, the outline of the polygon becomes a set of parabolic splines, one spline for the first and second line segments, one for the second and third, and so on. Straight-line segments can be generated in a smoothed polygon by duplicating the end-points of the desired line segment.
<B>-splinestepsB> => number Specifies the degree of smoothness desired for curves: each spline will be approximated with number line segments. This option is ignored unless the <B>-smoothB> option is true.
<B>-stateB> => state Modifies the state of the polygon item where state may be set to one of: normal, disabled, or hidden. A polygon item may also be in the active state if the mouse is currently over it. Many options can take separate specifications in normal, active and disabled states such that the appearance of the item can be different in each state.
<B>-stippleB> => bitmap
<B>-activestippleB> => bitmap
<B>-disabledstippleB> => bitmap This option specifies stipple patterns that should be used to fill the the polygon in its normal, active and disabled states. bitmap specifies the stipple pattern to use, in any of the forms accepted by <B>Tk_GetBitmapB>. If bitmap is an empty string (the default), then filling is done in a solid fashion.
<B>-tagsB> => tagList Specifies a set of tags to apply to the item. TagList consists of a list of tag names, which replace any existing tags for the item. TagList may be an empty list.
<B>-updatecommandB> => command Specifies a callback that is to be executed every time the polygon item is updated on the screen.
<B>-widthB> => outlineWidth
<B>-activewidthB> => outlineWidth
<B>-disabledwidthB> => outlineWidth
Specifies the width of the outline to be drawn around the polygon, in its normal, active and disabled states. outlineWidth may be in any of the forms described in the COORDINATES section above. OutlineWidth specifies the width of the outline to be drawn around the polygon, in any of the forms described in the COORDINATES section above. If the <B>-outlineB> option hasn’t been specified then this option has no effect. This option defaults to 1.0.

Polygon items are different from other items such as rectangles, ovals and arcs in that interior points are considered to be ‘‘inside’’ a polygon (e.g. for purposes of the <B>find closestB> and <B>find overlappingB> methods) even if it is not filled. For most other item types, an interior point is considered to be inside the item only if the item is filled or if it has neither a fill nor an outline. If you would like an unfilled polygon whose interior points are not considered to be inside the polygon, use a line item instead.

RECTANGLE ITEMS

Items of type <B>rectangleB> appear as rectangular regions on the display. Each rectangle may have an outline, a fill, or both. Rectangles are created with methods of the following form:



 $canvas->createRectangle(x1, y1, x2, y2, ?option, value, option, value, ...?)



The arguments x1, y1, x2, and y2 give the coordinates of two diagonally opposite corners of the rectangle (the rectangle will include its upper and left edges but not its lower or right edges). After the coordinates there may be any number of option-value pairs, each of which sets one of the configuration options for the item. These same option-value pairs may be used in <B>itemconfigureB> methods to change the item’s configuration. The following options are supported for rectangles:
<B>-dashB> => pattern
<B>-activedashB> => pattern
<B>-disableddashB> => pattern This option specifies dash patterns for the normal state, the active state, and the disabled state of a rectangle item. pattern may have any of the forms accepted by <B>Tk_GetDashB>. If the dash options are omitted then the default is a solid outline.
<B>-dashoffsetB> => offset The starting offset into the pattern provided by the <B>-dashB> option. <B>-dashoffsetB> is ignored if there is no <B>-dashB> pattern.
<B>-fillB> => color
<B>-activefillB> => color
<B>-disabledfillB> => color Specifies the color to be used to fill the rectangle in its normal, active, and disabled states. Color may be specified in any of the forms accepted by <B>Tk_GetColorB>. If color is undef (the default), then the rectangle will not be filled.
<B>-outlineB> => color
<B>-activeoutlineB> => color
<B>-disabledoutlineB> => color This option specifies the color that should be used to draw the outline of the rectangle in its normal, active and disabled states. Color may have any of the forms accepted by <B>Tk_GetColorB>. This option defaults to <B>blackB>. If color is undef then no outline will be drawn for the rectangle.
<B>-outlinestippleB> => bitmap
<B>-activeoutlinestippleB> => bitmap
<B>-disabledoutlinestippleB> => bitmap This option specifies stipple patterns that should be used to draw the outline of the rectangle in its normal, active and disabled states. bitmap specifies the stipple pattern to use, in any of the forms accepted by <B>Tk_GetBitmapB>. If the <B>-outlineB> option hasn’t been specified then this option has no effect. If bitmap is an empty string (the default), then the outline is drawn in a solid fashion.
<B>-stateB> => state Modifies the state of the rectangle item where state may be set to one of: normal, disabled, or hidden. A rectangle item may also be in the active state if the mouse is currently over it. Many options can take separate specifications in normal, active and disabled states such that the appearance of the item can be different in each state.
<B>-stippleB> => bitmap
<B>-activestippleB> => bitmap
<B>-disabledstippleB> => bitmap This option specifies stipple patterns that should be used to fill the the rectangle in its normal, active and disabled states. bitmap specifies the stipple pattern to use, in any of the forms accepted by <B>Tk_GetBitmapB>. If the <B>-fillB> option hasn’t been specified then this option has no effect. If bitmap is an empty string (the default), then filling is done in a solid fashion.
<B>-tagsB> => tagList Specifies a set of tags to apply to the item. TagList consists of a list of tag names, which replace any existing tags for the item. TagList may be an empty list.
<B>-updatecommandB> => command Specifies a callback that is to be executed every time the rectangle item is updated on the screen.
<B>-widthB> => outlineWidth
<B>-activewidthB> => outlineWidth
<B>-disabledwidthB> => outlineWidth Specifies the width of the outline to be drawn around the rectangle, in its normal, active and disabled states. OutlineWidth specifies the width of the outline to be drawn around the rectangle, in any of the forms described in the COORDINATES section above.

If the <B>-outlineB> option hasn’t been specified then this option has no effect. Wide outlines are drawn centered on the rectangular path defined by x1, y1, x2, and y2. This option defaults to 1.0.

TEXT ITEMS

A text item displays a string of characters on the screen in one or more lines. Text items support indexing and selection, along with the following text-related canvas methods: <B>dcharsB>, <B>focusB>, <B>icursorB>, <B>indexB>, <B>insertB>, <B>selectB>. Text items are created with methods of the following form:



 $canvas->createText(x, y, ?option, value, option, value, ...?)



The arguments x and y specify the coordinates of a point used to position the text on the display (see the options below for more information on how text is displayed). After the coordinates there may be any number of option-value pairs, each of which sets one of the configuration options for the item. These same option-value pairs may be used in <B>itemconfigureB> methods to change the item’s configuration. The following options are supported for text items:
<B>-anchorB> => anchorPos AnchorPos tells how to position the text relative to the positioning point for the text; it may have any of the forms accepted by <B>Tk_GetAnchorB>. For example, if anchorPos is <B>centerB> then the text is centered on the point; if anchorPos is <B>nB> then the text will be drawn such that the top center point of the rectangular region occupied by the text will be at the positioning point. This option defaults to <B>centerB>.
<B>-fillB> => color
<B>-activefillB> => color
<B>-disabledfillB> => color Specifies the color to be used to fill the text in its normal, active, and disabled states. Color may have any of the forms accepted by <B>Tk_GetColorB>. If color is undef then the text will be transparent. If this option isn’t specified then it defaults to <B>blackB>.
<B>-fontB> => fontName Specifies the font to use for the text item. FontName may be any string acceptable to <B>Tk_GetFontStructB>. If this option isn’t specified, it defaults to a system-dependent font.
<B>-justifyB> => how Specifies how to justify the text within its bounding region. How must be one of the values <B>leftB>, <B>rightB>, or <B>centerB>. This option will only matter if the text is displayed as multiple lines. If the option is omitted, it defaults to <B>leftB>.
<B>-stateB> => state Modifies the state of the text item where state may be set to one of: normal, disabled, or hidden. A text item may also be in the active state if the mouse is currently over it. Many options can take separate specifications in normal, active and disabled states such that the appearance of the item can be different in each state.
<B>-stippleB> => bitmap
<B>-activestippleB> => bitmap
<B>-disabledstippleB> => bitmap This option specifies stipple patterns that should be used to fill the the text in its normal, active and disabled states. bitmap specifies the stipple pattern to use, in any of the forms accepted by <B>Tk_GetBitmapB>. If bitmap is an empty string (the default) then the text is drawn in a solid fashion.
<B>-tagsB> => tagList Specifies a set of tags to apply to the item. TagList consists of a list of tag names, which replace any existing tags for the item. TagList may be an empty list.
<B>-textB> => string String specifies the characters to be displayed in the text item. Newline characters cause line breaks. The characters in the item may also be changed with the <B>insertB> and <B>deleteB> methods. This option defaults to an empty string.
<B>-updatecommandB> => command Specifies a callback that is to be executed every time the text item is updated on the screen.
<B>-widthB> => lineLength Specifies a maximum line length for the text, in any of the forms described in the COORDINATES section above. If this option is zero (the default) the text is broken into lines only at newline characters. However, if this option is non-zero then any line that would be longer than lineLength is broken just before a space character to make the line shorter than lineLength; the space character is treated as if it were a newline character.

WINDOW ITEMS

Items of type <B>windowB> cause a particular window to be displayed at a given position on the canvas. Window items are created with methods of the following form:

$canvas-><B>createWindowB>(x, y?, -option=>value, -option=>value, ...?)

The arguments x and y specify the coordinates of a point used to position the window on the display (see the <B>-anchorB> option below for more information on how bitmaps are displayed). After the coordinates there may be any number of option-value pairs, each of which sets one of the configuration options for the item. These same option-value pairs may be used in <B>itemconfigureB> method to change the item’s configuration. The following options are supported for window items:
<B>-anchorB> => anchorPos AnchorPos tells how to position the window relative to the positioning point for the item; it may have any of the forms accepted by <B>Tk_GetAnchorB>. For example, if anchorPos is <B>centerB> then the window is centered on the point; if anchorPos is <B>nB> then the window will be drawn so that its top center point is at the positioning point. This option defaults to <B>centerB>.
<B>-heightB> => pixels Specifies the height to assign to the item’s window. Pixels may have any of the forms described in the COORDINATES section above. If this option isn’t specified, or if it is specified as an empty string, then the window is given whatever height it requests internally.
<B>-stateB> => state Modifies the state of the window item where state may be set to one of: normal, disabled, or hidden.
<B>-tagsB> => tagList Specifies a set of tags to apply to the item. TagList consists of a list of tag names, which replace any existing tags for the item. TagList may be an empty list.
<B>-updatecommandB> => command Specifies a callback that is to be executed every time the window item is updated on the screen.
<B>-widthB> => pixels Specifies the width to assign to the item’s window. Pixels may have any of the forms described in the COORDINATES section above. If this option isn’t specified, or if it is specified as an empty string, then the window is given whatever width it requests internally.
<B>-windowB> => $widget Specifies the window to associate with this item. The window specified by $widget must either be a child of the canvas widget or a child of some ancestor of the canvas widget. PathName may not refer to a top-level window.

Note: due to restrictions in the ways that windows are managed, it is not possible to draw other graphical items (such as lines and images) on top of window items. A window item always obscures any graphics that overlap it, regardless of their order in the display list.

APPLICATION-DEFINED ITEM TYPES

It is possible for individual applications to define new item types for canvas widgets using C code. See the documentation for <B>Tk_CreateItemTypeB>.

BINDINGS

Canvas has default bindings to allow scrolling if necessary: <Up>, <Down>, <Left> and <Right> (and their <Control-*> counter parts). Further <Proir>, <Next>, <Home> and <End>. These bindings allow you to navigate the same way as in other widgets that can scroll.

Perl/Tk Methods

The following methods are added as perl code:
$canvas->get_corners Returns the bounding box in Canvas coordinates of the visible portion of the Canvas. (Written by Slaven Rezic.)

CREDITS

Tk’s canvas widget is a blatant ripoff of ideas from Joel Bartlett’s ezd program. Ezd provides structured graphics in a Scheme environment and preceded canvases by a year or two. Its simple mechanisms for placing and animating graphical objects inspired the functions of canvases.

KEYWORDS

canvas, widget
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