Feature Request: Subsurface Scattering

[defektu]

I was working on subsurface scattering implementation over Lit Shader. I did not wanted to open a PR because I'm not sure about implementation is mathematically right.

Here is the project that I've cleaned up for you guys. https://playcanvas.com/editor/scene/1751652 (?debug=true flag opens up gui.) https://playcanv.as/p/KW8u9ebM/?debug=true

Implementation

1. falloffLinearPS
   • Added LIGHTS_AVAILABLE for cross-checking.
   • pointLightCount - total point count
   • lightPointsPos[] - Array for light positions
   • lightPointsRad[] - Array for light rads;
2. lightDirPointPS - sets light positions
3. refractionDynamicPS
   • addSSS() - adds up sss effect on top of refraction shader.

Screenshots

SSS on SSS off

This is an old build but you can change some variables with dat.gui (debug=true flag opens up gui.): https://playcanv.as/index/ca8102ee

[defektu]

Made a ViolentMonkey script for quick test in editor. https://github.com/defektu/Playcanvas-Editor-Scripts Thanks to @yaustar for good example

[defektu]

Hi @mvaligursky , Do you think it would be a good feature implementation? I might create a PR about it.

[mvaligursky]

To be honest, perhaps not at the moment. I have few comments at the moment:

• we're trying to follow the glTF material model (including its extensions) for most part at the moment, and are hesitant to add many other functionality, especially if larger and harder to maintain
• your code uses separate arrays of light data, which is really not something I'd like to add to the core engine
• We'd need to make sure this is all physically as correct as it can be, which is non trivial and even you mentioned the doubts.

[defektu]

Thanks for the feedback Martin. Newly introduced arrays can be eliminated by using light" + i + "_position & light" + i + "_radius in lit-shader.js I assume. On physicaly correct part, I need to cross-check it cause of quick implementation. If you consider adding it as a render feature after glTF material model milestones just ping me up so I might work over it.

[mvaligursky]

Newly introduced arrays can be eliminated by using light" + i + "_position & light" + i + "_radius in lit-shader.js I assume.

But those are only available in non-clustered mode. Clustered mode encodes lights in textures and so this is harder to do this way.

[mvaligursky]

If you consider adding it as a render feature after glTF material model milestones just ping me up so I might work over it.

Absolutely. Please feel free to create an issue to implement SSS and link this PR there as WIP, so that we won't forget, thanks a lot!