Manual Reference Pages - BLIT (3)
blit - Copies a rectangular area from one bitmap to another. Allegro game programming library.
void blit(BITMAP *source, BITMAP *dest, int source_x, int source_y,
int dest_x, int dest_y, int width, int height);
Copies a rectangular area of the source bitmap to the destination bitmap.
The source_x and source_y parameters are the top left corner of the area
to copy from the source bitmap, and dest_x and dest_y are the
corresponding position in the destination bitmap. This routine respects
the destination clipping rectangle, and it will also clip if you try to
blit from areas outside the source bitmap. Example:
/* Blit src on the screen. */
blit(bmp, screen, 0, 0, 0, 0, bmp->w, bmp->h);
/* Now copy a chunk to a corner, slightly outside. /*
blit(screen, screen, 100, 100, -10, -10, 25, 30);
You can blit between any parts of any two bitmaps, even if the two memory
areas overlap (ie. source and dest are the same, or one is sub-bitmap of
the other). You should be aware, however, that a lot of SVGA cards dont
provide separate read and write banks, which means that blitting from one
part of the screen to another requires the use of a temporary bitmap in
memory, and is therefore extremely slow. As a general rule you should
avoid blitting from the screen onto itself in SVGA modes.
In mode-X, on the other hand, blitting from one part of the screen to
another can be significantly faster than blitting from memory onto the
screen, as long as the source and destination are correctly aligned with
each other. Copying between overlapping screen rectangles is slow, but if
the areas dont overlap, and if they have the same plane alignment (ie.
(source_x%4) == (dest_x%4)), the VGA latch registers can be used for a
very fast data transfer. To take advantage of this, in mode-X it is often
worth storing tile graphics in a hidden area of video memory (using a
large virtual screen), and blitting them from there onto the visible part
of the screen.
If the GFX_HW_VRAM_BLIT bit in the gfx_capabilities flag is set, the
current driver supports hardware accelerated blits from one part of the
screen onto another. This is extremely fast, so when this flag is set it
may be worth storing some of your more frequently used graphics in an
offscreen portion of the video memory.
Unlike most of the graphics routines, blit() allows the source and
destination bitmaps to be of different color depths, so it can be
used to convert images from one pixel format to another. In this
case, the behavior is affected by the COLORCONV_KEEP_TRANS and
COLORCONV_DITHER* flags of the current color conversion mode: see
set_color_conversion() for more information.
|Allegro ||BLIT (3) ||version 4.4.2 |
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