Add support for compressed texture

[x] Introduce ctx.TextureFormat as a mapping of [internalFormat]: [format, type], to automatically infer it in ctx.texture (WebGL2 ready)
[x] Update ctx.DataType to be used in ctx.TextureFormat with signed types (WebGL2 ready)
[x] Allow texture internalFormat/type as props (for compressed texture to pass their extension defined internalFormats)
[x] Make pixel format match internalType (keep Depth/Depth16/Depth24 as legacy)
[x] Check for ctx.capabilities.depthTexture to:
- fallback to internalType DEPTH_COMPONENT instead of DEPTH_COMPONENT16 (WEBGL_depth_texture only defines DEPTH_COMPONENT and STENCIL_COMPONENT, not DEPTH_COMPONENT16 etc)
- add DEPTH_COMPONENT and STENCIL_COMPONENT mapping to ctx.TextureFormat
[x] Fix premultiplyAlpha typo, width instead of height and opts.wrap order issues
[ ] Update docs

TBD:

Allow texture internalFormat/type as props (for compressed texture to pass their extension defined internalFormats): => Does it need to be an enum of supported compressed format instead? Or passing internalFormat is acceptable.
Is it okay to fallback to accepted data types in ctx.TextureFormat eg. in case gl.HALF_FLOAT is undefined, fallback to gl.FLOAT (R16F: [gl.RED, DataType.Float16], // DataType.Float32 could be R16F: [gl.RED, DataType.Float16 || DataType.Float32])

Any code using ctx.PixelFormat.R32F should be updated to:

ctx.texture2D({ pixelFormat: ctx.PixelFormat.Alpha, type: ctx.DataType.Float32 })

Do we need support for compressed texture for cubemaps?

https://github.com/pex-gl/pex-context/blob/9f2867dc3c1c316e62a3ed3f83a12da58aef63de/texture.js#L156-L157

Allow texture internalFormat/type as props

WWTJSD? WWBJSD? WWFD? :D

From my understanding when using gl.compressedTexImage2D the internalFormat replaces format and type as type is always binary blob. This way you could say pixelFormat is the internalFormat and just have:

const TextureFormat = {
  RGBA8UI: [gl.RGBA_INTEGER, DataType.Uint8],
  ...
  COMPRESSED_RGB_S3TC_DXT1: [ext1.COMPRESSED_RGB_S3TC_DXT1_EXT],
  ...
  COMPRESSED_RGBA_BPTC_UNORM: [ext2.COMPRESSED_RGBA_BPTC_UNORM_EXT]
  ...
}

But maybe it's not worth the effort because you would need to somehow map from magic int in ktx2 or gltf matching COMPRESSED_RGBA_BPTC_UNORM_EXT to COMPRESSED_RGBA_BPTC_UNORM (without _EXT) in order for it to work.

Now that i think more about it. Those constants still have to be defined somewhere... texture loader? What about the fact that some of them are _EXT in WebGL1 but in core in WebGL2?

Is it okay to fallback to accepted data types in ctx.TextureFormat eg. in case gl.HALF_FLOAT is undefined

That very much depends on use case. If for render targets where you wanna save on your big RGBA32F memory usage and opt-in for RGBA16F it would be fine. But single channel textures? I'm still confused though. How does one uses e.g. R16F? MDN says there are not color renderable and last time i have checked there was no way to upload Half Float data in WebGL1.

Any code using ctx.PixelFormat.R32F should be updated to: ctx.texture2D({ pixelFormat: ctx.PixelFormat.Alpha, type: ctx.DataType.Float32 })

Because it's not compatible with WebGL2 usage of gl.RED? Shouldn't that be handled internally?

R32F: [isWebGL2 ? gl.RED : gl.ALPHA, DataType.Float32],

Also it seems there is typo and ctx.PixelFormat.Alpha should be ctx.gl.Alpha?

https://github.com/pex-gl/pex-context/blob/9f2867dc3c1c316e62a3ed3f83a12da58aef63de/index.js#L259-L262

Depth, Depth16, Depth24 are just so our code doesn't break right? As you suggest we use WebGL2 style uppercase for everything?

Do we need support for compressed texture for cubemaps?

Definitely now now. I haven't used cubemap texture for like 5 years outside of render targets. It could be useful in webgl2 once seameless cubemaps are supported are we implement some of the glTF extensions for IBL which i think use cubemaps.

https://github.com/pex-gl/pex-context/blob/9f2867dc3c1c316e62a3ed3f83a12da58aef63de/index.js#L177-L178

What are those? WebGL1 vs WebGL2 mappings?

https://github.com/pex-gl/pex-context/blob/9f2867dc3c1c316e62a3ed3f83a12da58aef63de/index.js#L233

Will those more exotic formats be null in WebGL1?

Should i do those comments in commits not here? So they can be answered inline?

pex-gl / pex-context

Add support for compressed texture #100