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.TH "al_premul_rgba_f" "3" "" "Allegro reference manual" ""
.SH NAME
.PP
al_premul_rgba_f \- Allegro 5 API
.SH SYNOPSIS
.IP
.nf
\f[C]
#include\ <allegro5/allegro.h>
ALLEGRO_COLOR\ al_premul_rgba_f(float\ r,\ float\ g,\ float\ b,\ float\ a)
\f[]
.fi
.SH DESCRIPTION
.PP
This is a shortcut for al_map_rgba_f(3)(r * a, g * a, b * a, 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]
float\ r\ =\ 1;
float\ g\ =\ 0;
float\ b\ =\ 0;
float\ a\ =\ 0.5;
ALLEGRO_COLOR\ c\ =\ al_premul_rgba_f(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_f(3), al_premul_rgba(3)
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