Changing opacity of transparent material forces shader recompilation

[lucaheft]

Description

When changing the opacity intensity of a material which was initially set to 1, to some smaller value a shader recomplication is forced.

This seems to happen because MAPFLOAT isn't defined when the intensity is set to 1.
Technically this is correct, because multiplying by 1 doesn't change the ouput. However this introduces micro stutter for the first time the transparent material is faded.

I advocate for always including the intensity in the shader code. As the advantages farly outweigh the disadvantage.

The same applies for emissive intensity and probably a few others.

Pros

• Fewer shader variants
• No additional shader compilation

Cons:

• Additional multiplication in shader

Steps to Reproduce

1. Launch https://playcanvas.com/project/1200988/overview/bug-shader-generation
2. After a delay of 2 seconds the cube fades in and out
3. Shader of material TransparentRed is generated a second time
4. Shader generation is logged to console

[mvaligursky]

Yep fully agreed, we discussed this and few similar material parameters before. Same for tinting parameters, and likely some others.

[lucaheft]

Is this on the agenda for some of the next releases? This is bugging us for quite a while.

Or maybe you are open for a PR for this. I had quick look in the standard-material-options-builder.js and it should be a pretty straight forward change. But I'm still not too knowledgeable on the rendering part of the engine.
I also get it if you want a complete PR which includes all the changes on this topic, instead of only opacity and emissive tint.

[Maksims]

Is this on the agenda for some of the next releases? This is bugging us for quite a while.

Or maybe you are open for a PR for this. I had quick look in the standard-material-options-builder.js and it should be a pretty straight forward change. But I'm still not too knowledgeable on the rendering part of the engine. I also get it if you want a complete PR which includes all the changes on this topic, instead of only opacity and emissive tint.

As a temporary workaround you can use: material.setProperty('material_opacity', opacity) material.setParameter('material_opacity', opacity), which avoids shader recompilation.

[lucaheft]

setProperty does not seem to be a function of material.
There is setParameter, but it doesn't prevent shader recompilation.
The only workaround I found so far is to set max opacity to 0.999 to prevent shader compilation.

[willeastcott]

@lucaheft PRs are always welcome! 🙏

[Maksims]

setProperty does not seem to be a function of material. There is setParameter, but it doesn't prevent shader recompilation. The only workaround I found so far is to set max opacity to 0.999 to prevent shader compilation.

setParameter - yes, you are right.
But it does not trigger re-compilation. It does not mark the material to recompile shader (dirty flag on material). It is the most efficient way to set uniform. You can also do it for mesh instance btw.