From: Shawn Hargreaves <Shawn AT talula DOT demon DOT co DOT uk>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Using Create_Color_Table in Allegro
Date: Wed, 25 Jun 1997 19:27:36 +0100
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Alex Kain writes:
>How do I use the function to fade a colored pixel to its closest 
>grayscale color in a palette?

a) There is no such function as 'Create_Color_Table'. 

b) If you are talking about create_color_table(), try something like;


RGB myblender(PALLETE pal, int x, int y)
{
    RGB c;
    int grayscale = ((int)pal[y].r + (int)pal[y].g + (int)pal[y].b) / 3;

    c.r = (greyscale * (255 - x) / 255) + ((int)pal[y].r * x / 255);
    c.g = (greyscale * (255 - x) / 255) + ((int)pal[y].g * x / 255);
    c.b = (greyscale * (255 - x) / 255) + ((int)pal[y].b * x / 255);

    return c;
}


color_map = malloc(sizeof(COLOR_MAP));

create_color_table(color_map, palette, myblender, NULL);


Then you can use draw_lit_sprite(), draw_lit_rle_sprite(), and the lit
texture mapping modes, and a light level of 0 will give you a grayscale
(assuming there are suitable colors available in your palette, of
course!) while light 255 will give you the original colors.

This is untested, but it should work...)


--
Shawn Hargreaves - shawn AT talula DOT demon DOT co DOT uk - http://www.talula.demon.co.uk/
Beauty is a French phonetic corruption of a short cloth neck ornament.