Sokol: Missing WebGL2 features

[ilar81]

According to fact that base functionality for Sokol is WebGL I found out some missing features that presented in WebGL2.

• occlusion query
• transform feedback
• copy texture image
• copy buffer
  As far as I know all these features are supported by all other Sokol's backend 3D APIs. Are these features planned for the future?

[floooh]

Hi, one of the reasons is that the "base API" for sokol-gfx is "WebGL/GLES2 with common extensions", and it doesn't make much sense to require WebGL2 for the base functionality until Safari supports it IMHO.

But each of the points has different reasons (I also need to do some more research on some of the points):

• Transform feedback: I already had that working in Oryol for the GL/WebGL2 backend a while ago but decided to remove this again since it's hard to wrap under a common API for the different backends. The main problem was the shader side. The vertex shaders would look totally different between GL and Metal for instance, and AFAIK those differences can't be 'emulated' in shader cross compilers like SPIRVCross.
• Occlusion query: I probably wouldn't put this into the main API but into a separate extension header, since it's a fairly exotic feature and also not supported in Metal on all iOS devices (see https://developer.apple.com/metal/Metal-Feature-Set-Tables.pdf)
• copy images: makes sense as long as no format conversions or scaling is involved (which might limit its usability, a render pass which reads the source texture and renders into a target texture might be the more flexible solution)
• copy buffers: doesn't seem to be supported by WebGL or WebGL extensions (only WebGL2?)

[amerkoleci]

@floooh any plans to add more pixel formats? maybe would be cool to have kind of feature check for formats?

[floooh]

@amerkoleci yes, we can add more pixel formats, the current list is very conservative. Do you have a wishlist? Putting optional formats behind sg_query_feature() is also ok.

[amerkoleci]

I think all pixel formats, we can take look at metal pixel formats or vulkan and just check in backend if supported, for example I would remove rgb pixel format as only supported on opengl, I can submit some PR

[amerkoleci]

Or maybe bgfx pixel formats for example

[amerkoleci]

I think sokol can gain compute shader support as there are WebGL 2.0 compute specs (https://www.khronos.org/registry/webgl/specs/latest/2.0-compute/), I will work for D3D11 on my game framework if you want.

[floooh]

We should investigate whether it makes sense to add things like compute as an optional sokol-gfx extension header (e.g. sokol_gfx_compute.h) which could be optionally included after the sokol_gfx.h implementation, such an extension header would have access to the private data structs and functions of the sokol_gfx.h implementation and could add new public API functions.

The internal shader creation functions in the 3D API backends probably need to be made a bit more flexible, but that sounds doable.