NAME

SK — Agar dimensioned 2D sketch

SYNOPSIS

#include <agar/core.h>
#include <agar/sk.h>

DESCRIPTION

The Agar SK class implements a general-purpose 2D "sketching" engine with dimensioning and geometrical constraint solving. Sketches define a set of elements and a set of relations between those elements.

Elements are organized in a tree (the same structure is used to described group and leaf nodes). Each element in the graph is associated with a transformation matrix. The major sketch elements are points, lines and arcs, but other types can be added through a class registration interface.

Relations represent geometric constraints affecting points, lines, circles, segments and arcs. The following constraints are implemented:

• Parallelism
• Incidence
• Perpendicularity
• Tangency
• Concentricity
• Colinearity
• Explicit distance
• Explicit angle

The SK_View(3) widget is commonly used to display and edit SK objects.

INHERITANCE HIERARCHY

AG_Object(3) -> SK.

INITIALIZATION

SK *
SK_New(void *parent, const char *name);

The SK_New() function allocates, initializes, and attaches a SK object.

NODE MANIPULATION

void
SK_RegisterClass(SK_NodeOps *ops);

void
SK_NodeInit(void *node, const SK_NodeOps *ops, Uint flags);

void *
SK_NodeAdd(void *pnode, const SK_NodeOps *ops, Uint flags);

void
SK_NodeAttach(void *pnode, void *node);

void
SK_NodeDetach(void *pnode, void *node);

The SK_RegisterClass() function registers a new node class, described by the given SK_NodeOps structure.

The SK_NodeInit() function initializes the given SK_Node structure. It is usually invoked from node constructor functions. ops points to the SK_NodeOps structure which contains class information. The flags argument should be 0. The SK_NodeAdd() variant also allocates, initializes and attaches the node to a parent node.

The SK_NodeAttach() and SK_NodeDetach() functions attach/detach a node to/from a given parent.

NODE TRANSFORMATIONS

These functions multiply a node's transformation matrix T with a translation, scaling or rotation matrix. They are only aliases for M_Matrix * functions, except that they accept a pointer to a node instead of a matrix.

void SK_Translatev(SK_Node *node, M_Vector3 v)

void SK_Translate2(SK_Node *node, M_Real x, M_Real y)

void SK_Scalev(SK_Node *node, M_Vector3 v)

void SK_Rotatev(SK_Node *node, M_Real theta, M_Vector3 axis)

void SK_Rotatevd(SK_Node *node, M_Real degrees, M_Vector3 axis)

void SK_GetNodeTransform(void *node, M_Matrix44 *T)

The
SK_Translate*(); functions multiply T by a 2D translation matrix.

The
SK_Scalev(); function multiplies T by a 2D scaling matrix.

SK_Rotate*(); multiply T by a 2D rotation matrix. Angles are given in radians, except for
SK_Rotate*d(); variants which accept angular arguments in degrees.

SK_Rotatev(); generates a rotation of theta radians around axis. The
SK_Rotate*(); variants with the "d" suffix accept angles in degrees instead of radians.

The
SK_GetNodeTransform(); function returns a matrix which is the product of the transformation matrices of the given node and all of its parents.

SEE ALSO

M_Matrix(3), M_Vector(3), SG_Intro(3), SK_View(3)

HISTORY

The SK engine first appeared in Agar 1.6.0.