[vtkusers] Volume Rendering and zbuffer

[Aashish Chaudhary]

Hi Steve,

If you intend to get the depth values from volume (and not just geometry),
then not clearing the depth buffer will not help either since we don't
write to depth buffer (the defaults won't make sense anyways). If you are
looking for depth values from both volume and geometry, then you may want
to look into this option RenderToImage in the base class (
https://github.com/Kitware/VTK/blob/master/Rendering/Volume/vtkGPUVolumeRayCastMapper.h).
Give it a try and let us know if that works for you. If you enable this
option then you can call GetColorImage and GetDepthImage for the depth
values.

Thanks,


On Tue, Oct 4, 2016 at 12:34 PM Aashish Chaudhary <
aashish.chaudhary at kitware.com> wrote:

> That is because we make a call to clear the depth buffer bit  that is:
> glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT). I have to think all of
> the use-cases but I think we don't need to clear the depth buffer. We can
> push a simple fix for it on the master branch.
>
> - Aashish
>
>
>
>
> On Tue, Oct 4, 2016 at 12:12 PM stevep <steve.petruzza at gmail.com> wrote:
>
> Hi all,
>
> I used the vtkPolyDataMapper to render a surface and then with the
> vtkRenderWindow I can get correctly the ZBuffer using GetZbufferData and
> the
> RGB data via vtkWindowToImageFilter.
>
> When I use, starting from the same vtkImageData, a volume rendering like
> the
> SmartVolumeMapper (as in the following):
> http://www.vtk.org/Wiki/VTK/Examples/Cxx/VolumeRendering/SmartVolumeMapper
>
> The RGB data are correct but the ZBuffer contains all values == 1 (checked
> dumping the float array to disk).
>
> I get the same result changing blend mode and using a
> vtkFixedPointVolumeRayCastMapper.
>
> What am I missing?
>
> Thank you
>
>
>
>
>
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