Waveform, Parade and Vectorscopes were calculated by copying the
rendered image, transforming it into display space, and calculating
the the scope from that. On large resolutions, this
copy+transform+free of the image was taking up majority of the time.
Especially for default case when the display transform is a no-op.
Change the code so that display transform, if needed, is done directly
inside scope calculation, without needing a full-size temporary image.
Additionally, the vectorscope calculation was single threaded.
Multi-thread it by doing a parallel reduction, where each job
calculates their own scope image, and they are merged. Since job
payload is fairly large (512x512 bytes), make jobs pretty large
(256k pixels each).
Time (in ms) taken to calculate scope at 4K resolution (Ryzen 5950X,
Windows). Default color management settings:
- Waveform, PNG/SDR: 5.5 -> 5.2
- Waveform, EXR/HDR: 33.5 -> 10.3
- Vectorscope, PNG/SDR: 32.4 -> 4.5
- Vectorscope, EXR/HDR: 53.2 -> 9.8
Timings when additional color space management is needed (display
space set to Display P3, sequencer kept at sRGB):
- Waveform, PNG/SDR: 29.5 -> 10.9
- Waveform, EXR/HDR: 67.6 -> 10.9
- Vectorscope, PNG/SDR: 56.8 -> 12.0
- Vectorscope, EXR/HDR: 85.9 -> 13.4
This also fixes calculation of waveform / vectorscope on float (HDR)
images that have alpha channel; the scope was wrongly calculated on
premultiplied color values, which was not consistent with how it was
calculated on the byte images.
Pull Request: https://projects.blender.org/blender/blender/pulls/144059
8222cb0cfd