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Hi Gib.<br>
<br>
Proper blending of transparent objects is only possible by rendering
them in the correct order.<br>
This can be tricky and if objects or polygons overlap you even won't
get away with sorting them...<br>
You probably want depth peeling for order-independent transparency:
<a href="http://www.vtk.org/Wiki/VTK/Depth_Peeling">http://www.vtk.org/Wiki/VTK/Depth_Peeling</a><br>
<br>
Best Regards,<br>
<br>
Kim<br>
<br>
<div class="moz-cite-prefix">Am 10.08.2014 01:48, schrieb Gib Bogle:<br>
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<div style="direction: ltr;font-family: Tahoma;color:
#000000;font-size: 10pt;">The problem is simply demonstrated
with the opacity example:
<br>
<a moz-do-not-send="true"
href="http://www.vtk.org/Wiki/VTK/Examples/Cxx/Visualization/Opacity"
target="_blank">http://www.vtk.org/Wiki/VTK/Examples/Cxx/Visualization/Opacity</a><br>
<br>
Adding this line:<br>
sphereActor->SetPosition(1.0,0.0,0.0);<br>
and setting the opacity of both actors to 0.99 gives an
unexpected and unattractive result.<br>
<br>
I see that there have been posts about problems with
opacity/transparency as far back as 2006. Maybe there is a
solution...<br>
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font-size: 16px">
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<div style="direction: ltr;" id="divRpF830592"><font
color="#000000" face="Tahoma" size="2"><b>From:</b>
vtkusers [<a class="moz-txt-link-abbreviated" href="mailto:vtkusers-bounces@vtk.org">vtkusers-bounces@vtk.org</a>] on behalf of Gib Bogle
[<a class="moz-txt-link-abbreviated" href="mailto:g.bogle@auckland.ac.nz">g.bogle@auckland.ac.nz</a>]<br>
<b>Sent:</b> Sunday, 10 August 2014 11:25 a.m.<br>
<b>To:</b> <a class="moz-txt-link-abbreviated" href="mailto:vtkusers@vtk.org">vtkusers@vtk.org</a><br>
<b>Subject:</b> [vtkusers] Odd opacity issue<br>
</font><br>
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<div style="direction:ltr; font-family:Tahoma;
color:#000000; font-size:10pt">Hi,<br>
I'm using vtkRenderWindowInteractor (VTK 5.10) in Qt,
rendering spheres. I'm trying to implement a degree of
transparency, like this:<br>
<br>
<span style="color:#800000">actor</span><span
style="color:#000000">-></span>GetProperty<span
style="color:#000000">()-></span><span
style="font-style:italic; color:#000000">SetOpacity</span><span
style="color:#000000">(</span><span
style="color:#800000">opacity</span><span
style="color:#000000"></span><span style="color:#000000"></span><span
style="color:#000000"></span><span style="color:#800000"></span><span
style="color:#000000">);</span><br>
<br>
applied to all the spheres.<br>
<br>
If opacity is less than 1 the image immediately changes in
unexpected ways. See the two attached images, with
opacity = 1.0 and 0.99. It looks as if spheres have had
their positions and sizes changed. But when I rotate the
scene it becomes apparent that something else is
happening. Some of the "foreground" spheres move from
left to right (for example) while others apparently in the
foreground are moving right to left. It seems that the
order of rendering of the spheres, which normally places
the most remote first and the nearest last, has somehow
been messed up, so that spheres at the back are being
rendered last so that they appear to be the closest.
Maybe the order has been simply reversed, but the visual
effect is made more confusing by parallax - my brain is
interpreting the bigger spheres as closer.<br>
<br>
Is this a well-known issue, and is there a simple way to
fix it?<br>
<br>
Thanks<br>
Gib<br>
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