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Hopefully simple VFX question

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Matt Hornback
Hopefully simple VFX question
on Apr 9, 2010 at 2:41:06 am

Hi, and thank you in advance!

I'm working on a VFX shot in Maya 2010, with an empty background plate of a street. I've rebuilt the geometry of the street and surrounding buildings and applied the "use background" shader to catch shadows from my character (a large robot).

In the shot, the robot gets hit with a missile and I've keyed the intensity of a point light to simulate the flash of the explosion. This lights my character perfectly and the raytrace shadows are caught by the "use background" shader on the street and buildings.

Here's the problem: I don't know how to simultaneously catch the color of the light and the shadows from my character on all the background objects while leaving transparency wherever there is no light/shadow. To rephrase: I have created an explosion that lights the character and casts shadows, but doesn't light my background objects/plate.

Thanks for any and all help! I promise to pay it forward.


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Michael Frank
Re: Hopefully simple VFX question
on Apr 18, 2010 at 5:04:51 pm

Hey, I noticed its been some time since your post so you may have found some solution by now.

I guess that Use Background Shader can't be affected by lights. The best way to handle this would probably be to set it up in a compositor. Render out a separate pass of your geometry, where you use a different shader affected by the light. Then somehow apply that to the background layer in post - add or multiply for example.

You will also need to break up your scene to have a separate shadow and character pass.


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Matt Hornback
Re: Hopefully simple VFX question
on Apr 18, 2010 at 8:46:47 pm

Thanks for the reply! That's exactly what I ended up doing, the use background shader for straight shadows and another pass with a transparent blinn and a cranked specularity to catch the explosion light.


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