The Persistence of Vision Raytracer (POV-Ray).

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Attached to Project: POV-Ray
Opened by Kai Schwebke - 2010-04-09
Last edited by Chris Cason - 2010-12-31

FS#94 - Unexpected refraction angle in interfaces with changing IOR <> 1.0

I’ve tried to model this setup:
http://kschwebke.webng.com/povray/ior-interfaces/drawing.png with the following SDL:

A small overlap between the two transparent solids is needed, because a gap
would lead to total reflection. The camera in the test scene looks in the
direction of the ray in the setup drawing. The setup is surrounded with angular
markers, so one can easily read the final resulting looking angle.

POV-Ray 3.6.1 renders the expected result (~53° in the center of the screen):

POV-Ray 3.7.0b35a (compiled Unix source) renders a different
(and in my opinion wrong) angle (~67°), however – for the very same scene file:

I’ve started a discussion about this issue in povray.beta-test: http://news.povray.org/povray.beta-test/thread/%3Cweb.4bba4677730ab9f3e8c084b40%40news.povray.org%3E/

All linked documents are also attached.

Closed by  Chris Cason
Friday, 31 December 2010, 14:39 GMT
Reason for closing:  Fixed
Christoph Lipka commented on Monday, 12 April 2010, 16:40 GMT

Should be mostly fixed with task #4938.

The behavior will still be wrong (and different to 3.6 behavior) when the two objects almost - but not quite - touch each other, with a gap of something around ca. 1e-5 units or smaller. I suspect that overlap in this order of magnitude may still cause unexpected behavior in certain circumstances, too.

Grimbert Jérôme commented on Monday, 09 August 2010, 07:25 GMT

Looks like fixed: rendering of original scene is now similar 3.6 when done with 3.7beta38 from source (on amd64)

To render on Ubuntu, I had to install the msttcorefonts package, and add a +L/usr/share/fonts/truetype/msttcorefonts in the command line
(as well as removing the hard coded path of the font in the original scene).

Grimbert Jérôme commented on Thursday, 30 December 2010, 10:24 GMT

Tested with beta 41.
Updating scene to add #version 3.7; at the start, render is still ok. Can be closed.


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