From: "A. Jans-Beken" <jansb000 AT wxs DOT nl>
Newsgroups: comp.os.msdos.djgpp
Subject: Allegro: Lighting tables - how to?
Date: Sat, 02 Jan 1999 16:34:24 +0100
Organization: World Access
Lines: 33
Message-ID: <368E3C7F.94F8802F@wxs.nl>
NNTP-Posting-Host: vl0082-0.dial.wxs.nl
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Transfer-Encoding: 7bit
X-Trace: reader3.wxs.nl 915291567 9234 195.121.18.82 (2 Jan 1999 15:39:27 GMT)
X-Complaints-To: abuse AT wxs DOT nl
NNTP-Posting-Date: 2 Jan 1999 15:39:27 GMT
X-Mailer: Mozilla 4.04 [en] (Win95; I)
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp
Reply-To: djgpp AT delorie DOT com

I can't figure out how to use the lighting tables in allegro. I have red
the docs and looked at the example programs. I want to create an effect
(described later) and I think that lighting tables should do the trick.
However everything that I try results in something different than what I
expect -> a clear indication that my understanding has gaps.

What I want is create realistic shadow effects:
I have a sprite S, a shadow mask M and a tile T. To create nice effects
with shadow I first draw the tile to a buffer. Next, I draw the shadow
mask with draw_lit_sprite. Finally I draw the sprite with normal
draw_sprite. In a program this would look like this:

void draw_with_shadow(SPRITE& s, SHADOW& m, TILE& t) {
   BITMAP *buffer;

   // 1) Tile fills buffer.
   blit(... t to buffer ...);

   // 2) Shadow reduces intensity with 50%
   draw_lit_sprite(... m to buffer with color 128 ...);

   // 3) Sprite is draw normally.
   draw_sprite(... s to buffer ...);

   // 4) Copy the result to the screen.
   blit(... buffer to screen ...);
   }

Two questions:
- How do I have to initialize a COLOR_MAP to get this effect?
- Someone has some example code?