Support webgl2 and GLSL 3.00

[yoshikiohshima]

Another attempt to support WebGL2RenderingContext and GLSL 3.00.

• WebGLRenderer.js parameter may specify to call getContext() with argument 'webgl2'.
• Such a renderer allows to use GLSL 3.00.
• The share code in ShaderChunk and ShaderLib has #ifdef to switch between "varying/attribute" vs. "in/out".
• Multiple Render Target can be specified from the client code.
• extensions natively supported by WebGL2RenderingContext are handled.

(For our project, we have a GPGPU framework that uses GLSL3.00 features such as texelFetch and new buffer types such as R32F. This patch allows integrating the framework with Three.js. It's been working well for our purpose, and hopefully it is useful for others who are trying a similar stuff.)

[takahirox]

Do you wanna join the discussion here? #12250

[takahirox]

And #9965 is for WebGL2.0.

[mrdoob]

Rather than adding ifdefs macros everywhere... I would, instead, change the relevant varying to in directly in the .glsl files.

Then I would add a convertToGLSL1() function which would replace in with varying . That same function could also remove out vec4 glFragColor; and replace glFragColor = to gl_FragColor = .

Seems like sooner or later we would need this anyway.

[yoshikiohshima]

Great! When I started, I was not sure if all of those changes can be done mechanically. In the end, it was the case (I think).

By following some code in WebGLProgram.js, it may not be too hard to provide the source to source translation (without really parsing the GLSL code.)

[mrdoob]

That's what I hope!
Would you like to give a go to my suggestion?

[yoshikiohshima]

I just would like to check with you on the style of my JS, and how much assumptions I can have on the GLSL code. Basically my convertToGLSL1() would look like:

https://gist.github.com/yoshikiohshima/7083198c6eb7efdc82627de11e351f72

On my computer, it seems to be working. (The function is kind of long, but not too long.)

One thing I wonder about is that a use of glFragColor such as:

gl_FragColor = textureCube( tCube, vec3( tFlip * vWorldPosition.x, vWorldPosition.yz ) );

can't go multiple lines. So far I don't see a case like that so it maybe okay but somehow it'd have to be understood.

If this is good enough, I'll double check things (hopefully tomorrow) and make another pull request.

[yoshikiohshima]

Superceded by #13701.