Fix bloom luma calc in sRGB

[aevyrie]

Objective

• Luminance is a physical value that should be calculated in linear, not logarithmic (perceptual) space.

Solution

• Don't convert from linear to srgb to do a luma calc.

[github-actions]

Your PR caused a change in the graphical output of an example or rendering test. This might be intentional, but it could also mean that something broke!
You can review it at https://pixel-eagle.com/project/B04F67C0-C054-4A6F-92EC-F599FEC2FD1D?filter=PR-22565

If it's expected, please add the M-Deliberate-Rendering-Change label.

If this change seems unrelated to your PR, you can consider updating your PR to target the latest main branch, either by rebasing or merging main into it.

[IQuick143]

Makes sense. (Pedantic: srgb is not logarithmic.)

[IQuick143]

I figured the two changed screenshots are an intentional consequence of the code.

[mockersf]

I don't have an opinion: do we want to alter the examples to have a similar bloom as before or not?

[github-actions]

It looks like your PR is a breaking change, but you didn't provide a migration guide.

Please review the instructions for writing migration guides, then expand or revise the content in the migration guides directory to reflect your changes.

[alice-i-cecile]

I'd like a small migration guide for this, even though it's a bug fix. Tracking down the cause of changes to bloom intensity and how to correct it will be a huge pain otherwise.

[superdump]

Makes sense to me

[alice-i-cecile]

Linter is mad at you but this looks good :)