Path: chuka.playstation.co.uk!news1.scei.co.jp!scea!greg_labrec@interactive.sony.com
From: mperdue@iquest.net (Mario Perdue)
Newsgroups: scea.yaroze.programming.2d_graphics
Subject: Re: Texture page code
Date: Sat, 03 May 1997 14:32:49 GMT
Organization: SCEA Net Yaroze News
Lines: 44
Message-ID: <336b49e8.999305@205.149.189.29>
References: <01bc5782$52939560$8f91b8cd@mannynaj>
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>Whilst I was learning about using sprites, I found a piece of code that I
>-thought- I understood, but I just wanted to make sure:
>
>void FindTopLeftOfTexturePage (GsIMAGE* imageInfo, int* x, int* y, int* u,
>int* v)
>{
>
> ...
> ...
>
>}
>
>Methinks that this chunk of code is used to find a place to store the image
>data for a texture page.  Is this right?

It looks like it is trying to find the Upper left corner and offsets
of a full screen PAL image relative to a texture page. Without seeing
the code that calls this function, I couldn't tell you why it would be
used.

>
>Also, I found that people were using this:
>
>Sprite->attribute = |=<<25
>
>Does that set the 25th bit?  If so, how would you turn off the 25th bit?  I
>apologize for my lack of knowledge on this simple matter, but the only
>experience with bits I've had was on the Z80 processor.  SET A,7... it
>doesn't get any easier than that.

Yes, that code is intended to set a bit. I think you may have typed it
wrong though (someone correct me if I'm wrong.) I think it should be:

	Sprite->attribute |= 1<<25;

This say to take the value 1 shift it to the left 25 bits and OR it
with the original value. It's pretty much the same technique I told
you about earlier, just a different way to represent the bit.

You would still turn it off the way I showed you before, unless
someone else has a trick I don't know about.

>Manny Najera