create_trans_table(3alleg4)      Allegro manual      create_trans_table(3alleg4)

       create_trans_table - Fills a color mapping table for translucency
       effects. Allegro game programming library.

       #include <allegro.h>

       void create_trans_table(COLOR_MAP *table, const PALETTE pal, int r, g, b,
       void (*callback)(int pos));

       Fills the specified color mapping table with lookup data for doing
       translucency effects with the specified palette. When combining the
       colors c1 and c2 with this table, the result will be a color somewhere
       between the two. The r, g, and b parameters specify the solidity of each
       color component, ranging from 0 (totally transparent) to 255 (totally
       solid). For 50% solidity, pass 128.

       This function treats source color #0 as a special case, leaving the
       destination unchanged whenever a zero source pixel is encountered, so
       that masked sprites will draw correctly. This function will take
       advantage of the global rgb_map variable to speed up color conversions.
       If the callback function is not NULL, it will be called 256 times during
       the calculation, allowing you to display a progress indicator. Example:

          COLOR_MAP trans_table;
          /* Build a color lookup table for translucent drawing. */
          create_trans_table(&trans_table, pal, 128, 128, 128, NULL);

       color_map(3alleg4), create_light_table(3alleg4),
       create_color_table(3alleg4), create_blender_table(3alleg4),
       draw_trans_sprite(3alleg4), draw_lit_sprite(3alleg4),
       draw_gouraud_sprite(3alleg4), rgb_map(3alleg4), ex3d(3alleg4),

Allegro                           version 4.4.3      create_trans_table(3alleg4)