compositor: blend with multiple threads

Increases the throughput of compositing by using more CPU cycles across multiple threads. Simple cases (the output contains one pixel from at most one input) can have up to a 70% increase in throughput. Not so simple cases are limited by the region with the most number of composite operations.

added Performance label

approved this merge request

added Merge after freeze label

Needs rebase around _draw_background and _should_draw_background usage after !764 (merged)

added 37 commits

• e8c0b276...2d69cd56 - 36 commits from branch gstreamer:master
• ad636026 - compositor: blend with multiple threads

Compare with previous version

added Post release label and removed Merge after freeze label

assigned to @gstreamer-merge-bot

mentioned in commit ystreet/gst-plugins-base@7de39406

added 25 commits

• ad636026...8d645e1a - 24 commits from branch gstreamer:master
• 7de39406 - compositor: blend with multiple threads

Compare with previous version

assigned to @ystreet and unassigned @gstreamer-merge-bot

I couldn't merge this branch: CI failed!

assigned to @gstreamer-merge-bot and unassigned @ystreet

assigned to @ystreet and unassigned @gstreamer-merge-bot

I couldn't merge this branch: CI failed!

CI fails reproducibly.

assigned to @gstreamer-merge-bot and unassigned @ystreet

resolved all threads

mentioned in commit ystreet/gst-plugins-base@3c6c955d

added 18 commits

• 7de39406...d0f36c7e - 17 commits from branch gstreamer:master
• 3c6c955d - compositor: blend with multiple threads

Compare with previous version

assigned to @ystreet and unassigned @gstreamer-merge-bot