Path: chuka.playstation.co.uk!news
From: "Craig Graham" <c_graham@hinge.mistral.co.uk>
Newsgroups: scee.yaroze.programming.2d_graphics
Subject: Re: Caches
Date: 17 Aug 1998 22:24:28 GMT
Organization: PlayStation Net Yaroze (SCEE)
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Robert Swan <rs108@mdx.ac.uk> wrote in article <35D87238.2CBE@mdx.ac.uk>...
> Craig Graham wrote:
> so can i draw the conclusion that when a draw texture command is reached
> within the ordering table, then it automatically sticks the top left of
> the texture from the vram into the texture cache(unless of course its
> already got the same texture in it) and then doesnt move the stuff in
> the texture cache again, so benefits from the cache only come when it is
> drawing the top - left of the texture which happens to be in the cache?

Nope. It sticks the currently accessed square of the texture into the
cache.
The cache is only so big (see Jame's earlier post). If the whole of the
texture
for the poly you are displaying fit's into the cache you'll get good
performance.
If you have a lot of poly's using the same texture, and it fit's in the
cache
you'll get best performance.

So, if you're rendering a large poly with a large texture on it, the
renderer will
go along one line of a texture and then off the edge and then require a
texture
that's not in the cache. If you subdivide the poly so that each sub-poly
uses
a bit of the texture that fits into the, then it will draw a whole poly
without
requiring a cache re-load, and given that you will probably see a single
texture
pixel being stretched across several display pixels, this gives an
improvement
in draw time (a higher percentage of the pixels written come from the cache
rather than from the main VRAM).

> wierd :)

Not really ;)

> Rob

Is this helping?

Craig.