Path: chuka.playstation.co.uk!news
From: laura smith <laura_smith@interactive.sony.com>
Newsgroups: scee.yaroze.programming.2d_graphics
Subject: Re: Dynamic PIXEL & CLUT Creation ?
Date: Tue, 29 Apr 1997 09:58:57 +0100
Organization: Sony Computer Entertainment Europe
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Alex Amsel wrote:
> 
> On 26 Apr 1997 08:25:04 GMT, "Chris Allmark" <ZooSoft@compuserve.com>
> did quoth at me:
> 
> >I'm trying to create (as a test) a single pixel in VRAM without using a TIM
> >file.
> >I have tried to write a value (1 << 5) to a VRAM location for my pixel, and
> >16 x (0x7FFF) for my 15 bit color values. I have then assigned my sprite to
> >the pixel location, and the clut (4 bit) to the CLUT. It doesn't work.
> >
> >I have assumed that the 4 bit pixel value (0001) points to the second
> >address in the CLUT to find out what colour it should be. What am I doing
> >wrong ?
> 
> I'm a little confused by what you mean but I'll try and help...
> 
> If writing a pixel direct to the screen buffer, remember that it must
> be done with LoadImage and that the values are 16 bit (1,5,5,5) and
> cannot refer to cluts.
> 
> If trying to set up a sprite by directly writing to vram remember that
> if the sprite is 16 colours (4 bit) then 1 'pixel' of vram = 4
> 'pixels' of your sprite.
> 
> i.e. Each vram pixel is 16 bits long, and in those 16 bits you have
> pixel 1 | pixel 2 | pixel 3 | pixel 4
> 
> For an 8 bit clut it would be 2 pixels per vram word rather than 4.
> 
> Remember you must use LoadImage, and remember that as a non blocking
> function it returns before actually having copied the pixel. Use a
> DrawSync to ensure it has done so.
> 
> If you have done all this then perhaps you could post the source to
> look over?
> 
> Does the sprite work if you initialise vram from a normal time file?
> 
> * Alex Amsel * Into Beyond Web Design & JAVA Programming *
> * http://www.intobeyond.com  *  WWFC Utter Rubbish 1996-7*
> MM - "Steve Corica is every bit as good as that Kinkladze"


If you look at the SCEE 2d2 demo, I think part
of that directly writes colours into CLUTs and into arrays,
then loads them onto the frame buffer.

Main causes of error when programming this:
(i) pixel compression differs under 4, 8 and 16 bit modes
(ii) ensure finish of loading to VRAM, using DrawSync(0)
(iii) GsSPRITEs need correct bit-depth flag (again, 4, 8, 16)



Hope this helps


Lewis