Custom Shader - Get Light Data (Like Diffuse Direct or Shadow Pass)

[cgxev]

Hi,

I’m looking for a method to somehow get the light information as a black & white shader. This will help me visualize and iterate much faster and create interesting effects. Of course, you can do this via compositing, but that kills my flow.

To Illustrate:

If anyone knows a way to get this data without a custom script it will be much appreciated, otherwise I have to stick to compositing.

Thanks!

Cheers,
Beau

[Lumpengnom]

Maybe a pure white or gray shader in the override slot and then add a lot of contrast with the color managment “use curves” tool.

[lehuan5062 (Huân Lê-Vương)]

In Eevee there is a Shader to RGB node. It does convert light and shadow cast on the object to RGB color.

[cgxev]

Hey,

Thanks, yes, that is another good option, but since everything in Eevee is an estimation I need the accuracy of Cycles lighting.

Cheers,
Beau

[CarlG]

Basically, you can’t. Light and scene information is only available within enclosures which are available to and inside shader nodes only. In some cases, I use Shader2RGB in Eevee, render out the image, and use the image to drive material parameters using window coordinates.
You can do some faux shading effects based on an empty, but only from a single point “light source”, not any area lights.

[cgxev]

Thank you for your reply, this will only work on static scenes unless you render out the sequence. The feedback loop could be slower but worth giving a shot

[CarlG]

It doesn’t take long to render out the sequence from Eevee though.
Here an example where Shader2RGB is used to calculate hue variations from received light intensity, then simply referenced in the Cycles material as a screen coordinate image lookup for the glossy color.

My shading, textures, and material experiments

With 2.80 upcoming, I decided to do some experiments, and maybe convert some of the old stuff. For this first one I know that in Cycles we can’t (yet) do stuff that depends on scene brightness, but Eevee have this awesome Converter/ShaderToRGB node. With that in mind I loaded up the BMW test scene and used Eevee to generate a render where the color changes with how much light that pixel receives. That Eevee image comes out like this: [BMW_ColoredGlossy] I now simply mapped that image using …

May not look like much, but this kind of effect is not possible in Cycles. It wouldn’t work if the car was put on a mirror floor or seen through glass, but for this purpose the screen lookup worked just fine.