Transparent windows on wayland must be pre-multiplied after transfer-function encoding

[mahkoh]

Bevy version

0.17

What you did

Run the transparent_window example.

What went wrong

There is fringing where the bevy logo is translucent.

Additional information

Wayland assumes that pre-multiplication is performed after transfer-function encoding. There is no way to achieve this in Vulkan with built-in functionality, therefore I think the simplest solution to achieve this is as follows:

1. Keep everything else as is.
2. Immediately before presentation, run the following compute shader on the swapchain image:
   1. Apply the sRGB EOTF
   2. Unpremultiply
   3. Apply the sRGB OETF
   4. Premultiply

[mahkoh]

On the right you can see the bevy logo as intended. On the left you see the logo as displayed by the transparent_window application.