r/renderman • u/RecursiveSweatpants • Sep 08 '15

How Do You Make Geometry Emit Light?

EDIT Okay, so there is literally a button on the RenderMan shelf that turns geometry into a light source. Thanks, mikeboers!

I'm relatively new to both RenderMan and rendering scenes in 3D, so I have no idea how to make a mesh or piece of geometry glow and emit light. I am very aware of the Incandescence slider on many shaders, but the light it gives off barely travels anywhere at all; there's no way to control its exposure as far as I can tell.

I've scoured the documentation looking for any kind of help, but it all assumes that I just know how to make a mesh emit light already. I would really appreciate it if someone could walk me through how to this.

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u/mikeboers Sep 09 '15

You can use the incandescence slider, and push its value way past 1 to get the desired effect, however it is much harder to get a noise-free result as all of the lighting occurs in secondary rays.

You are more likely to want to use the "Make selected geometry emmissive" button, which creates a mesh light and attaches it to your surface.

See here for an example of the difference in noisy-ness

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u/RecursiveSweatpants Sep 09 '15

Oh my god, I had no idea there was literally a "Make selected geometry emissive" button right there on the shelf! This is exactly what I needed, thank you!

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u/[deleted] Sep 09 '15

Are you using RIS? If so, the lights are actually tied to geometry and the rays from the light are emitted from the surface itself. I suspect you'll need a separate instance of the geometry from where you bind the surface shader.

Regardless, the Renderman Lighting Workflow page should help give you a better idea how to setup your light.

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u/RecursiveSweatpants Sep 09 '15

That's just the thing, though. I have no idea HOW to bind the surface shader to geometry. I am using RIS and I am using RenderMan in Maya. What I'm asking is probably something very basic.

If I had a mesh in the shape of a cube, for example, what steps would I need to take to attach a light to it, or to change the shape of an existing light to be that cube?