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.TH "al_premul_rgba" "3alleg5" "" "Allegro reference manual" ""
.hy
.SH NAME
.PP
al_premul_rgba - Allegro 5 API
.SH SYNOPSIS
.IP
.nf
\f[C]
#include <allegro5/allegro.h>

ALLEGRO_COLOR al_premul_rgba(
   unsigned char r, unsigned char g, unsigned char b, unsigned char a)
\f[R]
.fi
.SH DESCRIPTION
.PP
This is a shortcut for al_map_rgba(3alleg5)(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(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:
.IP
.nf
\f[C]
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);
\f[R]
.fi
.PP
This function can be called before Allegro is initialized.
.SH SINCE
.PP
5.1.12
.SH SEE ALSO
.PP
al_map_rgba(3alleg5), al_premul_rgba_f(3alleg5)