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.TH "al_premul_rgba_f" "3" "" "Allegro reference manual"
.SH NAME
al_premul_rgba_f \- Allegro 5 API
.SH SYNOPSIS
.IP
.EX
#include \f[B]<allegro5/allegro.h>\f[R]

ALLEGRO_COLOR al_premul_rgba_f(float r, float g, float b, float a)
.EE
.SH DESCRIPTION
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
.EX
float r = 1;
float g = 0;
float b = 0;
float a = 0.5;
ALLEGRO_COLOR c = al_premul_rgba_f(r, g, b, a);
\f[I]/* Draw the bitmap tinted red and half\-transparent. */\f[R]
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_f(3), al_premul_rgba(3)