Path: chuka.playstation.co.uk!news
From: "Andrew Partington" <a.partington@yaroze41.freeserve.co.uk>
Newsgroups: scee.yaroze.beginners
Subject: CLUT lookup help!
Date: Wed, 8 Sep 1999 20:56:59 +0100
Organization: PlayStation Net Yaroze (SCEE)
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Message-ID: <7r7386$23b11@chuka.playstation.co.uk>
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Hi everyone!


I'm trying to write a pixel-perfect collision detection routine.  I've coded
one before in x86 asm on PC in mode13h (ahh, direct framebuffer access,
heaven!), but i'm having some trouble on the Yaroze version...

I have a 256 colour sprite, and I want to lookup the CLUT entry for each
byte of the sprite.  I am assuming that in 16 and 256 colour modes, the
sprite pixel data is actually an index into the CLUT, which contains the
correct colour, like the .PCX picture format.  I was expecting a copy of the
sprite to be inside the collision area, but when I LoadImage() the collision
area back to the visible screen to check what is going on inside the
collision area, the sprite I copied in is corrupted (and yes, I am doing a
DrawSync(0) after each LoadImage() and StoreImage() operation!).

I hope someone can help me out, I can't get my head round what's going on!
Below is my code for looking up CLUT entries for 256-colour sprite data, to
show what i'm trying to do (probably something daft!)

When I get it working, i'll stick the source on my page, so everyone can
benefit, and see the way not to do things :)

Cheers

Andy

a.partington@yaroze41.freeserve.co.uk
http://www.netyaroze-europe.com/~partinga



u_short* collisionArea;                    //64*64 array (8192 bytes)
u_short* clutArea;                            //malloc()'ed to 512 bytes,
containing a CLUT
u_char*  ufoArea;                            //16*8 area for enemy pixel
data

u_byte   index;
u_short    colour;
u_short    offset;

 for(ypos=0;ypos<8;ypos++)
 {
      for(xpos=0;xpos<16;xpos++)
      {

           index=ufoArea[ufoOffset];     //get byte from UFO array
           colour=clutArea[index];      //look up entry in CLUT
           collisionArea[offset]=colour;    //Put the entry in the collision
area

           ufoOffset++;
           offset++;
      }

      offset+=(64-16);        //-16 for sprite width
 }
        .... and then when the sprite has been written into the collision
area,
            the collision area is LoadImage()'d back to the visible screen
to
            see whats going on, and DrawSync(0) waited on!