al_premul_rgba(3)                                            al_premul_rgba(3)

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(3)(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(3) 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);


       This function can be called before Allegro is initialized.

SINCE
       5.1.12

SEE ALSO
       al_map_rgba(3), al_premul_rgba_f(3)

Allegro reference manual                                     al_premul_rgba(3)