Re: 3D texture size limitations in mesa/r200?

R. Aditya Kadambi wrote:
> Hi;
> 
> I am trying do hardware accelerated volume rendering with 3D textures
> using a scenegraph called OpenRM(www.openrm.org
> <http://www.openrm.org/>). The program is called vrend which uses 3D
> textures
> to HW render 3D raw data.
> 
> I am using ATI X9250 (R200) card. I am trying to render two sets of raw
> data. The smaller one which is 64x64x64 is successfully rendered with 3D
> textures with r200 driver. The bigger volume which is 256x64x256 only
> appears to be rendered in "half" along the z axis. The other half
> appears as garbage.
> 
> I put in a call for 3D texture size and it comes as 256 (which probably
> means I can render a 256x256x256 cube??).
> 
> I was able to successfully Software render it on Mesa. It renders fine.
> Furthermore, it is rendered fine with the ATI proprietary driver (V
> 8.28.8) (surprise! surprise!).
> 
> This makes me suspect the r200 driver. Is there an inherent limitation
> or a bug or a missing feature in the driver (r200/mesa) which might
> cause this. Is there any way for me to compile mesa with debug flags to
> test this? Or is there a bug in the lower level ati driver?
This should work. The hw seems to have a limit for the depth of a
texture of 256 (not sure why ati's driver can support more, maybe the
limit is actually not what's stated...), the other directions might
potentially work even up to 2048 (or not, maybe it would exceed the
internal range of the address calculation somewhere).
I suspect what's happening is that the driver exceeds the blitter limits
somewhere when uploading textures, since 3d textures are submitted to
the hw as huge 2d textures (well the width is normal but the height is
huge). There were similar problems in the past with large, mipmapped 2d
textures (the fix for that was 554e5a2eaf4b681b5c43b6aeb66f100a66da4a42).

Roland

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