[BUG] SKRuntimeEffect compilation is missing build-in functions

[Oribow]

Description

I've been trying out the new SKRuntimeEffect support in 2.88.0-preview.155 . Compilation of shaders using some opengl functions fails. (Tested with step and smoothstep). Not sure if this a skiasharp problem or a skia problem.

Code

uniform float2 iResolution; 
uniform float2 iPos; 

half4 main(float2 fragcoord) {
  float2 uv = (fragcoord - sk_FragCoord.xy) / iResolution.y;
  float d = length(uv);
  float m = 0.03 / d;
  m *= step(0.2, 0.3);
  return half4(m, m, m, m);
}"

Expected Behavior

This should compile. The same code works on the skia-sksl demo https://shaders.skia.org/.

Actual Behavior

Compilation outputs the following error:
error: 9: unknown identifier 'step'
This also happens with 'smoothstep'. Its weird that the 'length' function still works though. I have read that Skia only supports a subset of GL functions, but since it works on the demo site and these being very important shader functions, I doubt that they aren't included.

Basic Information

• Version with issue: 2.88.0-preview.155
• Platform Target Frameworks:
  • Android: 11 (API level 21)
  • Xamarin: 5.0.0.2244

[cyraid]

It errors with 'round' or 'mod' as well.. I'm wondering if it's 'cause it's a bit older of Skia? It kinda hampers the simple 'checkerboard' pattern shader I was gonna make. Not even 'coord.x % 32.0' works.

[LFLumirithmic]

Can confirm it fails with 'mod' as well. I'm using version 2.88.3 of SkiaSharp inside a .NET MAUI application. It would be great if support for these basic shader functions was added, especially since they work perfectly in the skia shader playground

[mattleibow]

Updating skia to the latest makes most of the functions work, however, the sk_FragCoord uniform is not actually available in the public spec. That is just for internal use by skia.

[mattleibow]

Duplicate of #2543