Problem with Water Shader Glass on scaled objects.

Started by Mr_Lamppost, January 02, 2009, 09:09:03 pm

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Mr_Lamppost

An issue has come to light concerning Water shader glass going dark when the scale of an object is increased.  Mandrake is  having problems with the glass in the lanterns of my Victorian Gas Lampposts rendering dark; see this topic over at terragen.org / Ashundar:

http://www.terragen.org/index.php?topic=4600.msg36566;topicseen#new

When I made tests I discovered that it the scale of the glass object is increased the glass appears dark.  Thinking about it logically I would expect the glass to appear  darker as the scaled glass is thicker relative to the Decay Distance set in the Water Shader. However when I increased the Decay Distance by the same factor by which the object was scaled the glass remained dark. Rather than continue with the glass from the lamppost lantern I made a simple test object consisting of a hollow cube with holes in three of its faces.  I then set up a test scene containing three copies of the thst object; the central instance is un-scaled, the one to the lower left is scald by a factor of 0.1 and is placed near the camera.  The third copy, top right is scaled by a factor of 10 and is placed further away.  All three share a single Water Shader.

The first series of images are identical except the the Decay Distance of the Water Shader is set to: 0.01, 0.1, 1, 10, 100 and 1000.  The un-scaled and  scaled down objects behave as I would expect but the scaled up version remains dark.

While I was typing this it occurred to me to test if any enlargement no matter how small created the problem.  Following a few tests it appears that a scale factor of two is the cutoff point.  For these tests I left the Water Shader unchanged with a Decay Distance of 10 and changed the scale of the test object the final two images show first the object scaled by 1.99999 and finally scaled by2.0. both scenes and the test object are included. 

There's not much more I can test so any comments or suggestions are welcome.  This may just be a limitation wee will have to live with but let's hope not.
Smoke me a kipper I'll be back for breakfast.