man fli_bmp_dirty_from () - Indicate which parts of the image have changed. Allegro game programming library.
NAME
fli_bmp_dirty_from, fli_bmp_dirty_to - Indicate which parts of the image have changed. Allegro game programming library.
SYNOPSIS
#include <allegro.h>
extern int fli_bmp_dirty_from;
extern int fli_bmp_dirty_to;
DESCRIPTION
These variables are set by next_fli_frame() to indicate which part of the fli_bitmap has changed since the last call to reset_fli_variables(). If fli_bmp_dirty_from is greater than fli_bmp_dirty_to, the bitmap has not changed, otherwise lines fli_bmp_dirty_from to fli_bmp_dirty_to (inclusive) have altered. You can use these when copying the fli_bitmap onto the screen, to avoid moving data unnecessarily. Example:
if (fli_bmp_dirty_from <= fli_bmp_dirty_to)
blit(fli_bitmap, screen, 0, fli_bmp_dirty_from,
0, fli_bmp_dirty_from, fli_bitmap->w,
fli_bmp_dirty_to - fli_bmp_dirty_from + 1);