create_trans_table(3)

💖 create_trans_table — bestie edition 💖

ok so this is a page from the Allegro manual, section 3, and it's all about create_trans_table. it's giving game-programming-glow-up energy and honestly? we're obsessed. ✨

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🌸 NAME 🌸

create_trans_table — fills a color mapping table for translucency effects. yep, it's the Allegro game programming library, and yes she's iconic for this one 💅

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🦋 SYNOPSIS 🦋

#include <allegro.h>

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

like, that's the whole signature. short. sweet. main character. 👑

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✨ DESCRIPTION ✨

okay so here's the vibe: create_trans_table fills the color mapping table you hand it (table) with lookup data for doing translucency effects with the palette you give it (pal). 🌈

when you combine the colors c1 and c2 using this table, the result is gonna be a color somewhere between the two. not one, not the other, a little secret third thing. no cap.

the r, g, and b parameters specify the solidity of each color component, ranging from 0 (totally transparent) to 255 (totally solid). so like:

• 0 = ghost mode, fully see-through 👻
• 255 = fully there, no notes
• and for 50% solidity, you pass 128. remember that number, bestie, it's the moment. 💖

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now for the special-case lore: this function treats source color #0 as a special case, leaving the destination unchanged whenever a zero source pixel is encountered — that way masked sprites draw correctly. it's the little detail that saves your whole render. 🫶

also, this function will take advantage of the global rgb_map variable to speed up color conversions. efficiency queen. ⚡

and if the callback function is not NULL, it will be called 256 times during the calculation, which means you can totally show off a progress indicator while it chugs along. 😭 so thoughtful.

example time, look at her:

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

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👀 SEE ALSO 👀

• color_map(3)
• create_light_table(3)
• create_color_table(3)
• create_blender_table(3)
• draw_trans_sprite(3)
• draw_lit_sprite(3)
• draw_gouraud_sprite(3)
• rgb_map(3)
• ex3d(3)
• extrans(3)

go read those too, they're all in the same friend group fr fr 🎀

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and that's the page!! this was Allegro, version 4.4.3, and the date on this one was the create_trans_table(3) era — so go forth and blend your sprites beautifully, bestie. you ate. 💅✨🦋