1al_premul_rgba_f(3) al_premul_rgba_f(3)
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6 al_premul_rgba_f - Allegro 5 API
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9 #include <allegro5/allegro.h>
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11 ALLEGRO_COLOR al_premul_rgba_f(float r, float g, float b, float a)
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14 This is a shortcut for al_map_rgba_f(3)(r * a, g * a, b * a, a).
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16 By default Allegro uses pre-multiplied alpha for transparent blending
17 of bitmaps and primitives (see al_load_bitmap_flags(3) for a discussion
18 of that feature). This means that if you want to tint a bitmap or
19 primitive to be transparent you need to multiply the color components
20 by the alpha components when you pass them to this function. For exam‐
21 ple:
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23 float r = 1;
24 float g = 0;
25 float b = 0;
26 float a = 0.5;
27 ALLEGRO_COLOR c = al_premul_rgba_f(r, g, b, a);
28 /* Draw the bitmap tinted red and half-transparent. */
29 al_draw_tinted_bitmap(bmp, c, 0, 0, 0);
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31 This function can be called before Allegro is initialized.
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34 5.1.12
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37 al_map_rgba_f(3), al_premul_rgba(3)
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41Allegro reference manual al_premul_rgba_f(3)