Fix upload of half-float textures in "WebGL 1"

[nkreeger]

Looks like this was regressed a few months ago here: #1375

I'm curious how this worked on iOS devices? From what I was told - Safari only supported OES_texture_half_float which enables creating gl.OES_HALF_FLOAT textures but allows them to write f32 data in gl.texSubImage2D().

Happy to discuss offline. But this essentially makes devices that only support f16 not work with the regression in texture manager.

This change is 

[nsthorat]

I don't think this will work on an iPhone -- we've always uploaded to 32 bit textures there (there is no way to upload to a 16 bit texture, I read the WebKit code :P)

[nkreeger]

Upload yes - from my understanding things work like this:

const oes = gl.getExtension('OES_texture_half_float');

// Create texture (for upload):
const t = gl.createTexture();
gl.bindTexture(gl.TEXTURE_2D, t);
...
gl.texImage2D(gl.TEXTURE_2D, 0, gl.RGBA, width, height, border, gl.RGBA, ext.HALF_FLOAT_OES, null);

// Now actually send values to texture:
const values = new Float32Array([0.5, 1.5, 2.5, 3.5]);
gl.texSubImage2D(gl.TEXTURE_2D, 0, 0, 0, 1, 1, gl.RGBA, gl.FLOAT, values);

Note that the texture has to be created as f16, but data can be uploaded via f32.

[nsthorat]

Have you tried that on an iPhone out of curiosity? That is the WebGL spec, but Apple iPhones fail most WebGL conformance tests.

[nsthorat]

By the way, that seems completely fine if this works on iOS :)

[nsthorat]

Actually, if this does work on iOS, we need to do a flag refactor. We don't have a flag for the upload type since it's unconditionally 32 bits right now (this is why you may be confused by the render / download flags).

[nsthorat]

Closing this out since it's old.