.\" Automatically generated by Pandoc 3.1.11.1 .\" .TH "al_premul_rgba" "3" "" "Allegro reference manual" "" .SH NAME al_premul_rgba \- Allegro 5 API .SH SYNOPSIS .IP .EX #include ALLEGRO_COLOR al_premul_rgba( unsigned char r, unsigned char g, unsigned char b, unsigned char a) .EE .SH DESCRIPTION This is a shortcut for al_map_rgba(3)(r * a / 255, g * a / 255, b * a / 255, a). .PP 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: .IP .EX 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); .EE .PP This function can be called before Allegro is initialized. .SH SINCE 5.1.12 .SH SEE ALSO al_map_rgba(3), al_premul_rgba_f(3)