External Output sRGB Write Fix / sRGB Preview Fixes

[peeweek]

• ✔ External Output sRGB Processing Fixes:
  • Removed Manual gamma correction
  • Added correct sRGB flag to texture importer
  • Added option to select either PNG or EXR file type for External Output, determines file type
• ✔Added an optional sRGB Preview to nodes
  • API defines its value previewSRGB , whether it can be edited per node canEditPreviewSRGB, and default value defaultPreviewSRGB
  • Defaults to MixtureNode are editable, and preview linear
  • Updated OutputNode not to use this preview (sRGB conversion already happens in finalOutputMaterial, so it is unnecessary to apply another conversion to the preview)
  • Updated External Output node to preview sRGB when configured correctly. Removed sRGB conversion in finalOutputMaterial (this conversion is handled by texture importer), Removed manual inverse-conversion that happened in C#.
  • Updated Input Texture Node : sRGB preview toggle only happens if input texture is not an imported texture. If this is an imported texture, sRGB preview is determined from the Texture importer

(Also added the sRGB toggle to the UIElements schema but it seems it is not used yet)

[peeweek]

I'm changing a bit how the external output file type works. Now there's an option to select either PNG or EXR (independently of the node precision). This allows to save the data from a FP16 directly to PNG and prevent that issue happening in LDR because of the SRGB Conversion. Color Conversion was happening in 8 bit as the node was output in that precision. Instead, the conversion can happen with default precision (FP16) without loss in the darkest tones.

The node has now an option for Texture2d dimension that allows selecting PNG or EXR as file type. Also, changing this type invalidates the update button.

[peeweek]

Some weirdness is that EncodeToEXR data can be fed into a PNG, caused me a headache, but finally fixed.

@alelievr : currently the PR is in an acceptable state regarding exported data and previews, however here's a summary of what could be improved:

1) need to find a way to manual color (reverse-)conversion happening at export (because we do a Linear>SRGB conversion in finalOutputMaterial and texture importer also does its own), right now the state of the PR is functional but the code is messy. 2) preview weirdness (low precision), could not find what is causing that.

stuff to do / questions:

• do we open another PR for fixing the previews / remove the extra conversions?
• do we add linear<->sRGB conversion nodes in this PR?
• do we add an option to control whether the previews are in gamma/linear ?

[peeweek]

Finally I have cleaned up the behavior in external output : no more conversion in finalOutputMaterial, and no more inverse-conversion in C#. Now, the conversion is only handled by the texture importer.

I have added a sRGB Preview System:

Preview can be implemented on any MixtureNode:

• implement an public override bool canEditPreviewSRGB => true|false; to enable the sRGB toggle in the preview of the node
• implement an public override bool defaultPreviewSRGB =>true|false; to define the default preview mode;
• in the node/nodeview, you can then alter the public bool previewSRGB; to control it manually

I've implemented specific behavior in 3 nodes:

• TextureNode has sRGB preview toggle only if input is not a texture with a TextureImporter, in that case value is read from the sRGB flag in the importer
• OutputNode never previews as sRGB, as the finalOutputMaterial handles the sRGB Conversion, it will be previewed correctly
• ExternalOutputNode previews depending if the output will be configured with the sRGB flag on. All other conversions were removed.