View Full Version : Shadow maps with transparent shadows?

01-25-2007, 12:13 AM
Is it possible to get transparent shadows with the shadowmap shadow type?
Ive looked through the help and cannot find any info on this....


01-25-2007, 12:21 AM
yes it is.
Under the shadow parameters just decrease density

01-25-2007, 12:41 AM
Under the shadow parameters just decrease density

True shadow transparency will evaluate the filter channel and filter color(s), so your statement is not true.

Other render engine and light types may support it, such as the 2 sided shadows checkbox, but I'm not totally clear on thier use.


01-25-2007, 08:01 AM
Yeah, the reason i want to use shadowmaps is beacuase their the only shadow type that doesnt ignore smoothing groups, hence give nice looking shadows on our lowpoly meshes. The downside is they dont cast shadows through alpha textures :(

Any ideas?

01-25-2007, 09:43 AM
Mental Ray shadow maps have an option to take transparency into account. It's turned off by default and you'll obviously need to use Mental Ray as a renderer to use them. Look in the Mental Ray Shadow Map rollout of the light (with MR shadow maps selected as shadow type) and you'll find a 'transparent shadows' section.

01-25-2007, 12:13 PM
Or you can use mental ray area shadows, they give a very nice result... If you want to go hardcore you can render out the spotlight view with your model 100% black, transparent areas still transparent on a white background and use that as a projector map. You will have to exclude your model from the light so it projects your image as the transparent shadows on the floor. You'll have to add a second light that illuminates your model but not the floor too.

Not very useful I know but at least you get 100% control over your transparent shadows :D

Chris Thomas
01-25-2007, 01:33 PM
Mental Ray lights support "Deep" shadow maps, which do indeed take transparency into account. They are also the best option for very fine geo (like hair) and translucent/transperent surfaces. However, they are also slower to calculate than standard shadow maps due to the high level of pre-filtering involved in them. Shouldn't be a problem on your low poly models though.


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