The R200 driver supports 3D textures of 256x256x256.

However, using an opensource OpenRM scenegraph (http://www.openrm.org), it looks like the volume is only rendered "half" in the Z direction.

For instance, a 256x256x32 volume would render right. But a 256x256x64 volume would render only "half" in the Z direction. The other half appears garbled.

This issue was discussed extensively on dri-users list. A patch was sent by Roland Scheidegger which fixed the issue on my FreeBSD system. The patch is reproduced here:

diff --git a/shared-core/radeon_state.c b/shared-core/radeon_state.c
index 4c85371..921a56e 100644
--- a/shared-core/radeon_state.c
+++ b/shared-core/radeon_state.c
@@ -1663,7 +1663,7 @@ static int radeon_cp_dispatch_texture(st
        u32 height;
        int i;
        u32 texpitch, microtile;
-       u32 offset;
+       u32 offset, byte_offset;
        RING_LOCALS;
 
        if (radeon_check_and_fixup_offset(dev_priv, file_priv, &tex->offset)) {
@@ -1841,6 +1841,7 @@ static int radeon_cp_dispatch_texture(st
                }
 
 #undef RADEON_COPY_MT
+               byte_offset = (image->y & ~2047) * image->width * (tex_width / tex->width);
                buf->file_priv = file_priv;
                buf->used = size;
                offset = dev_priv->gart_buffers_offset + buf->offset;
@@ -1855,9 +1856,9 @@ static int radeon_cp_dispatch_texture(st
                         RADEON_DP_SRC_SOURCE_MEMORY |
                         RADEON_GMC_CLR_CMP_CNTL_DIS | RADEON_GMC_WR_MSK_DIS);
                OUT_RING((spitch << 22) | (offset >> 10));
-               OUT_RING((texpitch << 22) | (tex->offset >> 10));
+               OUT_RING((texpitch << 22) | ((tex->offset >> 10) + (byte_offset >> 10)));
                OUT_RING(0);
-               OUT_RING((image->x << 16) | image->y);
+               OUT_RING(((image->x + (byte_offset % 1024) / (tex_width / tex->width)) << 16) | (image->y % 2048));
                OUT_RING((image->width << 16) | height);
                RADEON_WAIT_UNTIL_2D_IDLE();
                ADVANCE_RING();