Like blit(), but skips transparent pixels, which are marked by a zero in
256-color modes or bright pink for truecolor data (maximum red and blue,
zero green), and requires the source and destination bitmaps to be of
the same color depth. The source and destination regions must not overlap.
Example:
BITMAP *hud_overlay;
...
/* Paint hud overlay on the screen. */
masked_blit(hud_overlay, screen, 0, 0, 0, 0,
hud_overlay->w, hud_overlay->h);
If the GFX_HW_VRAM_BLIT_MASKED bit in the gfx_capabilities flag is set,
the current driver supports hardware accelerated masked 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
sprites in an offscreen portion of the video memory.
Warning: if the hardware acceleration flag is not set, masked_blit() will
not work correctly when used with a source image in system or video
memory so the latter must be a memory bitmap.
