WebGLRenderer: Remove inline sRGB decode.

[Mugen87]

Fixed #23109.

Description

This PR removes the sRGB inline decode in shaders. There are now new policies for sRGB workflows:

• WebGL 2 requires the usage of RGBA8 for uncompressed sRGB encoded textures.
• WebGL 1 now tries to use EXT_sRGB and the respective unsized formats. However, this only works by disabling mipmapping. If EXT_sRGB is not supported, a (slow) CPU decode is performed.

@sunag I've updated the node related code so that the examples still work. However, the node systems require some cleanup since methods like fromDecoding() and getTextureEncodingFromMap() should not be used anymore.

[mrdoob]

[mrdoob]

If EXT_sRGB is not supported, a (slow) CPU decode is performed.

I guess we can replace this later with a GPU approach? @kenrussell suggested creating a WebGLRenderTarget for each texture and converting to linear with a shader.

[Mugen87]

I've tried using render targets however this will making the code way more complex. The problem is that we can't trigger a render within WebGLTextures since this will mess up the uniform setup for the actual frame. Using WebGLRenderTarget would have to happen at an earlier stage. E.g. one could gather the sRGB encoded color textures in projectObject() and convert them. However, storing the converted textures without overwriting the original one is tricky, too. Besides, the current solution handles all sRGB encoded textures (even in custom shaders). Achieving the same with a render target approach is also more complicated.

Ideally, we don't have to go down this path and just use EXT_sRGB and CPU decodes until we completely remove WebGL 1 support.

[sunag]

@sunag I've updated the node related code so that the examples still work. However, the node systems require some cleanup since methods like fromDecoding() and getTextureEncodingFromMap() should not be used anymore.

@Mugen87 No problem! It seems easy to do.
Great PR this.

[mrdoob]

Thanks!

[makc]

until we completely remove WebGL 1 support.

and when is that, @Mugen87

[Mugen87]

see #22689 (comment)

[tangobravo]

I'm not a big fan of the CPU WebGL1 fallback - doing that sRGB -> linear conversion into an 8-bit texture is likely to introduce pretty severe banding artefacts that wouldn't be apparent with the conversion in the shader.