[vtkusers] AMD volume rendering issue

[ianl]

Hi all,

I have just upgraded my graphics card to an AMD Radeon HD 6770 and am now
finding that I am having problems with volume rendering. I notice other
people have had similar problems with ATI/AMD cards, but I believe my issue
is slightly different.

The symptom is that the volume rendered image appears black. I have put some
code in to parse the image data output and I have found that the image is
actually rendered with the alpha channel set for the pixels that would make
up the image, but the RGB values are set to a very low value. If I hack the
output data to set non zero pixels to white, the rendered image appears in
silhouette form, so some sort of rendering is taking place.

If I set shading off, the image appears ok, but obviously not shaded which
would point to an issue related to shading. I found a post from some time
ago mentioning this sort of behaviour with GPU ray casting on ATI cards
(can't seem to find it now). There was also a post mentioning negative Z
spacings for the original data causing issues, but mine are positive as far
as I can see.

I am using the vtkSmartVolumeMapper to do the volume rendering, and I have
traced the code through and it looks as if the smart mapper is choosing the
GPU ray caster as my card claims it supports the features required. If I
force it to do volume texture mapping by calling
SetRequestedRenderModeToRayCastAndTexture(), the image renders properly, so
this may do as an interim solution, but still suffers from the slow single
threaded resample I mentioned in a different post. I would like to use GPU
ray casting if available as the performance and results are much better.

I am using VTK 5.8 and Windows 7 SP1. The card drivers are up to date, and
GLView reports that OpenGL 4.1 is fully supported. I have even tried AMD's
OpenGL 4.2 Beta driver which makes no difference.

I am reasonably sure the pipeline and volume properties are set up correctly
as the image renders properly with the fixed point software ray caster. I
suspect that the answer will be that AMDs drivers are notoriously buggy, but
I am hopeful that someone else may have found a workaround.

Any ideas would be appreciated,
Ian Lindsay


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