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.TH "al_premul_rgba" "3" "" "Allegro reference manual" ""
.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[]
.fi
.SH DESCRIPTION
.PP
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
.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[]
.fi
.SH SINCE
.PP
5.1.12
.SH SEE ALSO
.PP
al_map_rgba(3), al_premul_rgba_f(3)
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