Skiasharp: [FEATURE] Expose SkSL?

[Ziriax]

It seems the SkSL has a public API, and had GPU and CPU backends.

Although Google says it is likely to change a bit since it is under active development.

Since back in the days even good old Silverlight had such a feature, I think it would make sense to expose it in SkiaSharp.

If so, I would be happy to make a PR.

[Gillibald]

I don't think that this will be useful because you need to compile shaders alongside Skia itself. If it would be possible to compile shaders at runtime this would be a killer feature.

[mattleibow]

I _think_ I saw a demo where the shader was just a string... So maybe? I have been keeping an eye on that and I think a runtime compilation might actually be something. I'll have a closer look...

[Ziriax]

According to the reply I got from Google in Skia discuss, it now has an interpreter and JIT...

In the CanvasKit fiddle you just pass a string:
https://jsfiddle.skia.org/canvaskit/33ff9bed883cd5742b4770169da0b36fb0cbc18fd395ddd9563213e178362d30

But that one is running on the GPU, so not a good reference...

I will ask more questions in Skia discuss, but if you have to precompile shaders, it is indeed limited.

We could of course write a backend for SkSL that generates SIMD ILASM ;-)

[mattleibow]

Keep up the discussion there! Then I can see what needs to be done to make it work well in SkiaSharp

[mattleibow]

For those following along at home https://groups.google.com/forum/#!topic/skia-discuss/LNCQs-7b7rk

[mattleibow]

I think it was @kekekeks was asking about this in the past?

[Gillibald]

Y being able to compile shaders at runtime would allow us to introduce custom effects.

[kekekeks]

Our idea was to provide GLSL text and a pointer to software implementation func. Proper SkSL with JIT on the Skia side would be indeed way better.

[Ziriax]

My feeling from following the discussion in the skia mailing list, is that the CPU implementation is currently a bit behind the GPU one.

My customer's current server side renderer uses DirectX 11 WARP, a purely software implementation of DirectX 11, so it seems Skia is not yet at that level, but its catching up (in 2008, WARP could run Crysis on a Core i7!)

Nevertheless I think that most users will use the GPU for rendering with Skia, and then exposing SkSL might be a really nice feature?

It seems one just needs to expose the SkRuntimeShader class, with some small helper structs. To pass data, Span<byte> could be used. Of course a much higher level interface could be provided, using .NET marshalling to provide the values of the uniforms, like SharpDX does.

[mattleibow]

Having a look right now. going to get a very simple thing working and see what happens. I should be working on actual issues, but COVID-19, right?

[Gillibald]

That's the positive side of the Corona crisis. Some people have more time to spend on things they love.

[mattleibow]

Good news folks! Things seem to be working!!! At least on Windows x64. Just tweaking the bindings and adding a few tests and then I'll push a branch for folks to play around with. Seems all we need is a string and we are off to the races!

[Ziriax]

That is great news! So you couldn't resist, hehe, I know the feeling ;-)

I guess in the longer term we will need some methods to transfer/marshal uniform data and SkShader instances to the runtime shader?

[mattleibow]

Hehe, no I couldn't. We might be able to do something with a "dictionary" type of thing for the inputs. There is some iterable object.
The tests have a possible starting point: https://github.com/google/skia/blob/5f6b41e6d8aa1ead3cbdb94a483bc8bea32e0fb3/tests/SkRuntimeEffectTest.cpp#L74-L90

[mattleibow]

I have the code here for now (https://github.com/mono/SkiaSharp/pull/1221).
The GPU bits seem to work - 1 simple test. The CPU needs some compiler options but I think the GPU is fine for basic testing and experimentation. I need to do actual work now...

Overall, this looks both simple and powerful. Let me know what you think. Looks cool so far.

[mattleibow]

Moved the code and changes to a new PR which is much better and I hope to get a working GPU package out: #1321

[mattleibow]

I have been doing some work on this... Let me know what you think: https://github.com/mono/SkiaSharp/issues/1319#issuecomment-640529824