[vtkusers] Bug in depth ordering whilst rendering

[Peter Clifton]

Do any developers hang out here?

I appreciate that having no reply to a question (in what is arguably a
short time so far), can indicate many things..

* Question asked in wrong place
* Question missing information
* Question containing too much information

If anyone is familiar with the rendering code, perhaps they will be able
to point me in the right direction.

I doubt this is a VTK bug in the strictest sense (as MESA software
rendering seemed to "fix" it), but without knowing what underlying cause
is, or having a simple gl / glut test case, reporting a MESA bug isn't
yet going to get much attention either.

Best wishes,

Peter C.


On Mon, 2007-11-26 at 21:21 +0000, Peter Clifton wrote:
> Hi,
>
> I'm visualising some wave data with VTK 5.0.3, and have encountered some
> strange issues with rendering.
> 
> When rotating views in some cases, some objects / surfaces always draw
> on top of others, despite them being at the back of the Z-Order for the
> scene.
> 
> Searching for a simple test case, I find that the "three planes" in the
> example: Examples/VisualizationAlgorithms/Python/TextureThreshold.py
> exhibits the symptom. I've been using Mayavi2, and the coordinate arrows
> you can add into the view also exhibit the bug, at certain angles
> objects at the back are drawn on top of closer objects.
> 
> In the TextureThreshold.py example, it seemed that changing the
> 
> The rendering 
>  "SetOpacity(0.999)" calls to some other value, e.g. 1.5 would stop the
> bug manifesting.
> 
> I've got an Intel 945GM graphics chip, and am using DRI with Mesa
> 7.0.1-1ubuntu3. Forcing DRI off (hence software fallback rendering in
> Mesa IIRC), the rendering works fine.
> 
> Can anyone point me the the appropriate VTK Rendering code so I might
> look and see which GL calls are relevant? (To go digging for what I
> presume to be an underlying driver bug). I've seen a wiki entry about
> depth peeling, but if I'm right, that isn't implemented in the 5.0.3
> release?
> 
> 
> Best wishes,
> 
-- 
Peter Clifton

Electrical Engineering Division,
Engineering Department,
University of Cambridge,
9, JJ Thomson Avenue,
Cambridge
CB3 0FA

Tel: +44 (0)7729 980173 - (No signal in the lab!)