<div dir="ltr">Basically it is OpenGL, in that OpenGL doesn't automatically tessellate concave polygons. Making VTK always examine every polygon to determine if it is concave would be a performance hit for everyone, so we leave it up to developers to use a triangle filter if they need it. <div><br></div><div>Thanks</div><div>Ken</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Oct 18, 2016 at 9:11 AM, Stefan Melber <span dir="ltr"><<a href="mailto:Stefan.Melber@dlr.de" target="_blank">Stefan.Melber@dlr.de</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div bgcolor="#FFFFFF" text="#000000">
<div class="m_-7630672803956935750moz-cite-prefix">Hi Martin,<br>
<br>
i tried the triangle filter in all cases - and yes - i works in
all three cases. <br>
<br>
So is this "problem" of concave polygons inside VTK or in OpenGL?
<br>
<br>
Best regards,<br>
<br>
Stefan<br>
</div>
<blockquote type="cite">
<div dir="ltr">I'm not sure if this is your issue, but you might
try using a triangle filter on your data. For OpenGL we do not
guarantee correct rendering of concave polygons. The triangle
filter will convert a concave polygon into convex triangles
which should render correctly.</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Tue, Oct 18, 2016 at 2:20 AM, Stefan
Melber <span dir="ltr"><<a href="mailto:Stefan.Melber@dlr.de" target="_blank">Stefan.Melber@dlr.de</a>></span>
wrote:<br>
<blockquote class="gmail_quote">
<div> Hi,<br>
<br>
i found a rendering problem with cuts through polyhedral
cells depending on which rendering backend is used. For
example in PV 5.1.2 compiled with<br>
<br>
VTK_RENDERING_BACKEND = OpenGL<br>
<br>
a cut looks like error.opengl.v5_1_2.png - there is a
wrong shading and some facets coming from the wrong
starting point.<br>
<br>
Switching to OpenGL2 everything is fine
(error.opengl2.v5_1_2.png). This problem is the same with
ParaView 5.2.0RC1 and OpenGL or OpenGL2 - however there
seems to be an additional (smaller) problem using OpenGL2:
there are some lines drawn outside of the shell - see
error.opengl2.v5_2_0rc1.png (cutted on a different
position).<br>
<br>
The example cell is for testing is attached as "error.vtk"
- cut e.g. in x-direction on different positions to get
the described effects.<br>
<br>
Best regards,<br>
<br>
Stefan<br>
<br>
<br>
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-- <br>
<div class="m_-7630672803956935750gmail_signature" data-smartmail="gmail_signature">Ken
Martin PhD
<div>Chairman & CFO<br>
Kitware Inc.<br>
28 Corporate Drive<br>
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</blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature" data-smartmail="gmail_signature">Ken Martin PhD<div>Chairman & CFO<br>Kitware Inc.<br>28 Corporate Drive<br>Clifton Park NY 12065<br>518 371 3971<div><br></div><div><span style="font-size:10pt;font-family:Tahoma,sans-serif">This communication,
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