NAME¶
al_premul_rgba - Allegro 5 API
SYNOPSIS¶
-
#include <allegro5/allegro.h>
ALLEGRO_COLOR al_premul_rgba(
unsigned char r, unsigned char g, unsigned char b, unsigned char a)
DESCRIPTION¶
This is a shortcut for al_map_rgba(3alleg5)(r * a / 255, g * a / 255, b * a /
255, a).
By default Allegro uses pre-multiplied alpha for transparent
blending of bitmaps and primitives (see al_load_bitmap_flags(3alleg5) for a
discussion of that feature). This means that if you want to tint a bitmap or
primitive to be transparent you need to multiply the color components by the
alpha components when you pass them to this function. For example:
-
int r = 255;
int g = 0;
int b = 0;
int a = 127;
ALLEGRO_COLOR c = al_premul_rgba(r, g, b, a);
/* Draw the bitmap tinted red and half-transparent. */
al_draw_tinted_bitmap(bmp, c, 0, 0, 0);
SEE ALSO¶
al_map_rgba(3alleg5), al_premul_rgba_f(3alleg5)
