Path: chuka.playstation.co.uk!news
From: Chris Chadwick <xjk18@dial.pipex.com>
Newsgroups: scee.yaroze.programming.2d_graphics
Subject: Re: CLUT troubles!
Date: Wed, 06 Aug 1997 01:14:57 -0700
Organization: PlayStation Net Yaroze (SCEE)
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References: <33E1AB7A.1DEE@dial.pipex.com> <33E1CBFC.42D@interactive.sony.com> <33E38861.2EC9@dial.pipex.com> <33E608B8.1225@interactive.sony.com>
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Developer Support wrote:
> 
> Chris Chadwick wrote:
> >
> > Hi Stuart
> >
> > I've attached a zip file containing a simple example to demonstrate the
> > problem (I hope you get it OK as I haven't sent an attached file before :)
> > It uses ClearImage() instead of MoveImage() to simplify things but the
> > problem is the same.
> >
> > Curiously, now that I've extracted the relevant code from my project
> > for the example, I now can't seem to change *any* of the CLUT entries;
> > not even the first 16 as I could before!
> >
> > I'm a bit worried that you say you have no problems changing all CLUT
> > entries. Perhaps I've missed something, but i can't think what.
> >
> > Your info that CLUTs have to be 16 pixel aligned has cleared-up the
> > 'shifted colour' problem. Thanks, I did not realize this.
> >
> > I'll post this to the newsgroups as well in case anyone else is
> > interested. Thanks for your quick response ;)
> >
> > Chris
> >
> > PS I'm using GNU development in case you need to know.
> >
> 
> OK, it seems that your CLUT is getting cached, and hence the changes are
> not taking effect. The only way I can think of fixing it is if you draw
> at least two different sprites, (or the same sprite with a different
> CLUT location). This will clear the CLUT and reload your altered one the
> next time round.
> 
> There maybe a better fix, I'll look into it.
> 
> Stuart

Sorted! :)

All behaves as expected when I add a second 8-bit sprite to the OT
although it has to have it's display attribute bit set otherwise it
doesn't work so, at the moment, I'm just using a 1x1 sprite with
negative screen coords.

All the other other sprites I'm displaying are 4-bit so I gather this
was why I was only able to alter the first 16 CLUT entries: they were
being changed in the CLUT buffer frequently for the various 4-bit
sprites, but my single 8-bit sprite meant that entries 16-255 were
never getting reloaded into this buffer...  I had no idea a CLUT
cache was being used!

Thanks for solving a particularly puzzling problem, Stuart - you're
a star ;)

Chris