This helper generates shader snippets that converts pixels from one
color state to another. For example if there is content with sRGB color
state that should be converted to linear BT.2020 before being written to
the framebuffer, a shader that makes the pixel go through the following
steps will be generated:
1. sRGB EOTF
2. Luminance gain (hard coded for now)
3. Color space mapping
The intention is that it should be possible to composite in a linear
color space, into an intermediate framebuffer, which is then passed
through an inverse EOTF to produce linear content in the output color
state.
When transforming from BT.2020/PQ to sRGB/sRGB, clamping to the sRGB
max luminance is done.
Cases where direct transform is also handled, i.e. where one doesn't go
via an linear intermediate buffer, in which case there might be both an
EOTF and an inverted EOTF in the same shader snippet to still do color
space mapping using optical color encoding. This will be used for e.g.
transforming cursor sprites.
Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3433>
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