From: Shawn Hargreaves <Shawn AT talula DOT demon DOT co DOT uk>
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Drawing in diffrent colours in Allegro
Date: Sat, 4 Jan 1997 14:13:43 +0000
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Andrew Ellem writes:
>I'd like some help on how to draw the same sprite in diffrent
>colours using Allegro.  I would like to draw a sprite, changing
>all bytes x to y.  
>
>Something like this : 
>draw_sprite(BITMAP *bmp, BITMAP *sprite, int x, int y, int c1, int c2);
>Where every c1 in the sprite would be changed to c2, in addition
>to ignoring the 0's.

I can think of three approaches:

You could preprocess your sprites into all the different colors you
need. Easy, but could take up a lot of space depending how many
different versions you have.

Alternatively you could write your own sprite drawer. Off the top of my
head, something like:

#include <sys/farptr.h>

draw_thingy(BITMAP *bmp, BITMAP *sprite, int x, int y, int c1, int c2)
{
   int xpos, ypos, pix;
   unsigned long address;

   _farsetsel(bmp->seg);

   for (ypos=0; ypos<sprite->h; ypos++) {
      address = bmp_write_line(bmp, y+ypos) + x;
      for (xpos=0; xpos<sprite->w; xpos++) {
         pix = sprite->line[ypos][xpos];
         if (pix) {
            if (pix == c1)
               pix = c2;
            _farnspokeb(address+xpos, pix);
         }
      }
   }
}

That should work for everything except mode-X screen bitmaps, although I
have to admit I haven't actually tested it :-) It doesn't do any
clipping, but I expect the speed will be adequate for most purposes...

Another possibility is to wait until I finish the translucency/lighting
code I'm working on at the moment. This will use a lookup table to blend
colors, and will provide several ways of drawing sprites, including one
which tints them to a different color using a lookup table to map every
color into a different color. Set up the lookup table correctly, and
you'll be able to do any number of c1->c2 conversions in a single step.
No promises how long this will take me to implement, though :-)

/*
 *  Shawn Hargreaves - shawn AT talula DOT demon DOT co DOT uk - http://www.talula.demon.co.uk/
 *  Ghoti: 'gh' as in 'enough', 'o' as in 'women', and 'ti' as in 'nation'.
 */