Shader Pipeline Roadmap

[pjcozzi]

Current offline uses cases

• Add default precision
• Add built-in constants, structs, and functions
• Add automatic uniforms

Current runtime use cases

• Concatenate sources for psuedo-polymorphism, e.g., czm_getMaterial (for materials), czm_computePosition (for the geometry pipeline), and czm_getFilter (for post processing).
• Add #defines for uber-shaders.
• main renaming for picking via createPickFragmentShaderSource for per-instance show in Primitive.js.
• Duplicate uniforms for precision - Duplicate uniforms shared between vertex and fragment programs on mediump-only devices #817

Items

• Pack uniforms for performance - Optimize setting uniforms #649
• GLSL minification. Similar to glTF #36.
  • We can't minify quite as much as some of these tools, but I think we can come pretty close now with the compile-time-ish shader concatenation.
• Write tech blog post.
• Handle precision correctly - Duplicate uniforms shared between vertex and fragment programs on mediump-only devices #817
  • In general, shader authors need to control precision; defaulting to highp for everything is suboptimal for mobile. See Fast Mobile Shaders. Should be benchmark and optimize existing shaders?
• Compile/link shaders on workers when there is a WebGL extension. CC WebGL 2 and WebGL Extensions Roadmap #797.
• Edit shaders in cache at runtime. See Cesium Inspector Roadmap #1025
• Route all shader usage through the shader cache. CC Cleanup renderer object creation #640

Ideas

• Scriptable automatic uniforms, i.e., instead of hardcoding in ShaderProgram.js.

Done

• Automatically prepend czm_ functions, types, and constants. Preserve useful line numbers with #line.
  • Unfortunately, this should probably include automatic uniforms even though we expect them to get optimized out.
  • Perhaps we can use the GLSL optimization for some of this.
• Make #define-based uber-shaders easier to use, i.e., no explicit string concatenation.
• GLSL optimization. Similar to glTF #34.
  • How hard is it to integrate this and below into our build?
  • Do we notice the performance improvement on different hardware, including mobile?
  • Does this or minification (below) affect shader compile/link time?

Reading

• Generating Shaders From HLSL Fragments
• A high level shader construction syntax - Intro has a concise overview of techniques

[fasiha]

This checklist makes me think there’s a tech blog post about this topic? I’m looking for some background on the topics mentioned in https://github.com/AnalyticalGraphicsInc/cesium/wiki/Screen-Space-Rendering-Details i.e., czm_getFilter etc.

[pjcozzi]

There's not a blog post about this, but general Cesium graphics blog posts are here: http://cesiumjs.org/blog.html#webgl

[fasiha]

Ah ok. Just to make sure: magic like this https://github.com/AnalyticalGraphicsInc/cesium/wiki/Screen-Space-Rendering-Details#example-filter-chain-scripts is just hypothetical right? This kind of post-rendering doesn’t exist right now?

[pjcozzi]

@fasiha that is a roadmap; it is not implemented, except for an incomplete prototype from a few years ago: https://github.com/AnalyticalGraphicsInc/cesium/compare/postprocess-hook