Transmissivity and Total Internal Reflection

General Forums Blender and CG Discussions
1

Just a recap on an earlier thread http://blenderartists.org/forum/showthread.php?t=64957 - the transmissivity patch got committed so you’ll expect to see better glass-like materials in the Blender Internal renderer in 2.42.

Results will go from this:

http://mediawiki.blender.org/uploads/b/b6/Without-transmissivity.jpg

To something more like this:

http://mediawiki.blender.org/uploads/7/7b/With-total-internal-reflection.jpg

Note the way the shadows vary with thickness and the glass feels richer. You adjust the “ray trans” filter value to reduce the transmissivity of the material, thus filtering out more and more light with the thickness of the object.

This is one of the first few material features which makes the volume of material meaningful, and not just the surface. I know some people are working on volumetric shading (flame, smoke, etc.) too, and I am looking into a low-cost subsurface scattering (SSS) approach to go into 2.43 or so.

The implications of volume for transmissivity (and later, SSS) are twofold:

  • You gotta pay attention to scale more. Transmissivity has to be tuned for the scene’s scale. If you design a glass object for a scene with 1 blender unit == 1 meter, your glass needs to be set to allow a lot less transmissivity (a higher filter value) than if you design a glass for a 1 blender unit == 1 centimeter sort of scene.

  • You still gotta pay attention to normals. Proper “manifold” meshes are not required, but if a ray leaks out of a mesh, the results will look funny. This is true without transmissivity too, but the transmissivity feature will give you even stranger results if you try to make a glass window with only one polygon instead of a true thickness, or if your normals are not facing outward from the object.

And thanks to those who supported my efforts and apologies to those who may have suffered from my impatience. :slight_smile:

2

Great news and a welcome addition indeed!
Thanks for your efforts in improving Blender. Much appreciated indeed!!

3

Cool. How important is this feature in creating realistic stuff?

4

I think it will be good for transparent objects like glass. I read about that on mediawiki stemming from a Blendernation link and it seems quite good that it got commited. Now when people do glass it will be a lot more realistic.

I’d love to do some cool glassy renders with this thing along with other transparent objects.

Congradulations, and hoping the recode will release a steady chain of rendering improvements from users.

5

:smiley: took longer than i hoped, but beaurocracy is always fun :smiley:

love this patch, i’ll be using it heaps and heaps.

Alltaken

6

This looks good, but just a couple of questions.

When it reduces light levels is it in any way related to the colour of the glass (ie does the glass look more coloured where it’s thicker)?

Would it potentially be possible to extend it so it blurs light through thicker sections more than thin ones?

Anyway, great stuff even if neither of the above are possible!

7

Thank halley,great stuff!
The only thing that I don’t like is the relation with the size of the object, a
scaling factor for this could be useful.
Btw,now we can do really good glasses,thank you:)