View Full Version : Help needed with rendering glass and shadows!!

11 November 2009, 01:05 PM

Im having problems rendering shadows for my glass shader. I really want to get realistic shadows, but the transparent shadows don't seem to be any lighter than shadows cast from solid objects. Below is a test render which I hope should demonstrate my problem.

Also if anyone has any tips for making my glass shader look any more realistic, that would be really helpful. Im currently using mia_material glass shader preset with some tweaks as my glass shader.

Thank you in advance

11 November 2009, 06:34 PM
In your mia_material's refraction area, make sure "refractive caustic" is on, and also that it's not thin-walled.

Perhaps try (in the reflection area) turning off "skip inside reflection", as well.

Another option is to use caustics (GI) if you aren't already. This can really lighten up your shadows, and also give them a more genuine glass refraction look.

11 November 2009, 11:57 AM
thanks for the response, unfortunately turning on refractice caustic automatically turns of transparent shadows, which then looses the redness in the shadow. :(

The skip inside reflection works well, I am currently using caustics but Im not sure if Im entirely using them right if theyre not that visible in the renders.

11 November 2009, 07:34 PM
Turning on caustics isn't so much "losing" the color of the shadow, but it's taking on a more physically accurate simulation of the light. This method takes a bit of tuning, but the results are much more realistic, especially inside your glass object.

Here's a quick example from an old scene I re-rendered to show you the difference:

With caustics (in the mia_material_x, "refractive caustic" setting) -

Without caustics (in the mia_material_x, "transparent shadow" setting) -

The second is more colorful, but not very "realistic" in terms of the shadows and how light transmits through the gemstones. In both, I've left the lights' shadow-casting at 0 radius, so they are "stark, hard" shadows, not soft. But you can see the difference in the gemstones themselves as well as the shadows being cast.

Hope this helps a bit. I can send you the scene if you want to play with it or something.

11 November 2009, 10:45 AM
cheers for all your help, it would be a big help if you could send me a copy of your file to play around with, thank you.

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