Re: fbsubtexload ?

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Sharon Clay (src++at++rose)
Tue, 27 Feb 1996 09:23:54 -0800

+>---- On Feb 27, 9:23am, Lionel Maiaux wrote:
> Subject: fbsubtexload ?
->
->On Feb 26, 4:00pm, Sharon Clay wrote:
->> Subject: Re: fbsubtexload available on Infinite Reality?
->>
->> +>---- On Feb 26, 5:25pm, Nicolas Gauvin wrote:
->> > Subject: fbsubtexload available on Infinite Reality?
->> ->
->> ->I would like to know if the Infinite Reality offers something
->> ->equivalent to the IRIS GL fbsubtexload and subtexload functions
->> ->that are available on Reality Engines.
->>
->> Yes. In OpenGL, this is the copy_texture OpenGL extension.
->> You can update all or part of a texture from the current GL_READ_BUFFER.
->> Sample routines are glCopyTexImage2DEXT() and glCopyTexSubImage2DEXT().
->> This is implemented on IMPACT as well.
->>
->
->I know that this OpenGL extension doesn't work very well on RE2 (it does not
->subload other levels of a mipmap texture than 0), and I would like to know :
->- if it's a system (5.3), an OpenGL implementation or an harware bug,

It is an RE implementation issue. The IRIS GL implementation had these
limitations on RE and the OpenGL implementation for RE has the same
basic functionality.

->- if this bug will be corrected in the future on these machines,

Absolutely - IMPACT and InfiniteReality do not have these limitations.

->
->If this extension works without bugs on Infinite Reality, it would be
->interesting to know a little more about subload performances :
->- what is the absolute cost (in ms) for the subload of a non-mipmapped and a
->mip-mapped texture with a given size ?

IR texture downloads are several times faster than RE and IMPACT and is
initially host limited. You should initially see 160+++MBytes/sec,
depending on CPU (R4K, R10K, ...).
With these kinds of rates, the real issue will be how fast you
can get the data off disk.

->- how does the texture size modify this cost ?

Bigger is always faster but I think you can do quite well wtih small
loads < 32x32.

->- what is the best place in the DRAW process to subload textures ?

At the end of the frame, loading them for the next frame.
This is because the IR has parallelism in the pipe that lets you fill
texture memory as you are doing rendering so you can overlap the
fill-limited time at the end of the frame with setting off the texture
downloads. Then, when you are ready to use the textures in the next frame
they will be ready. Doing it at the start of the frame will delay your
drawing and doing it on-demand wil cause interruptions
in the drawing stream.

src.

-- 
-----{-----{---++at++   -----{----{---++at++   -----{----{---++at++   -----{----{---++at++
Sharon Rose Clay (Fischler) - Silicon Graphics, Advanced Systems Dev.
src++at++sgi.com  (415) 933 - 1002  FAX: (415) 965 - 2658  MS 8U-590
-----{-----{---++at++   -----{----{---++at++   -----{----{---++at++   -----{----{---++at++

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