max 3D texture size on ATI X1800 512MB card


What is the maximum 3D texture that can be loaded on ATI X1800 512MB card? The theoretical limit is reported as 2048x2048x2048. However I am unable to load more than 512x512x600 (8-bit, GL_LUMINANCE).

nVIDIA 7800 GTX although having 512MB, limits 3D textures to 512x512x512. Any idea if this will be increased in future drivers?



Hint: 2048x2048x2048 = 2^33 = 8 Gb
512x512x600 ~ 2^27 = 127 Mb
(assuming 1 byte per texel).

The first limit is just teoretical, it’s not possible with 512 Mb videomem.

I think that 2048^3 refers to the maximum
size in each dimension, so e.g. a 2048x32x32
3D texture should work.

I did some testing, and it turns out ATI has the same limitation; glTexImage3D() calls work on 3D texures (8-bit, GL_LUMINANCE) upto 512x512x512 only. 512x512x1024 returns GL_OUT_OF_MEMORY.

I tried using in-between non-power-2 sizes, but the driver hangs.

Fine, so I try loading 2 512^3 8-bit textures, which amounts to 256MB. I still get GL_OUT_OF_MEMORY ! I don’t know why I’ve paid more for video memory that doesn’t seem to be getting used!

This sucks… Hope this is just a driver bug?
Has anyone had similar experiences?