WebGLRenderer: Remove gammaOutput, introduce outputEncoding.

[Mugen87]

As proposed in #11337.

This PR removes gammaOutput and introduces outputEncoding as a replacement. gammaOutput can still be used, however a warning will be generated. The renderer ensures to update materials if outputEncoding is changed during runtime.

There is in subtle change that needs some highlight: getTextureEncodingFromMap() does only depend from the given map now. That means the previous behavior of automatically setting the encoding of a render target's textures to GammaEncoding if gammaOutput is true does not exist anymore. This is also the correct behavior from my point of view. Meaning, when using post-processing via EffectComposer, WebGLRenderer.outputEncoding should not be changed and gamma correction should be done via ShaderPass and GammaCorrectionShader. Check out how webgl_materials_normalmap is written now to see this idea in action.

[WestLangley]

It is not appropriate to use both of these patterns in the same example:

renderer.outputEncoding = THREE.GammaEncoding;

texture.encoding = THREE.sRGBEncoding;

Doing so will cause color distortion.

In the examples, use THREE.sRGBEncoding for both texture encoding and renderer output encoding.

Some users prefer the flexibility of GammaEncoding in combination with renderer.gammaFactor. I think it would be appropriate to have one example use that case.

[Mugen87]

Doing so will cause color distortion.

I've just tried to retain the current visuals as good as possible. If things can be improved, I'm glad to do this with this PR.

[Mugen87]

I think it would be appropriate to have one example use that case.

Do you have an example already in mind?

[WestLangley]

It would have to be one without textures, I guess...

[Mugen87]

How about webgl_buffergeometry?

[WestLangley]

How about webgl_buffergeometry?

Or none. I don't have a strong opinion on that.

[Mugen87]

Then I would leave it out for now since the API is proper documented. If necessary, we can still update one of the examples in the future.

[mrdoob]

Many thanks!

[Mugen87]

Yay! It's great to get rid of gammeInput and gammaOutput in a single release^^

[mrdoob]

So many things are being solved in this release 😍

[Mugen87]

I would say it's the best release of 2019 😁

[mrdoob]

Getting it ready for the next decade 😀