NAME
blit - Copies a rectangular area from one bitmap to another. Allegro
game programming library.
SYNOPSIS
#include <allegro.h>
void blit(BITMAP *source, BITMAP *dest, int source_x, int source_y, int
dest_x, int dest_y, int width, int height);
DESCRIPTION
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:
BITMAP *bmp;
...
/* 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 don't 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 don't 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.
SEE ALSO
masked_blit(3alleg), stretch_blit(3alleg), draw_sprite(3alleg),
gfx_capabilities(3alleg), set_color_conversion(3alleg)