VSE timeline, when many (hundreds/thousands) of thumbnails were visible, was
very slow to redraw. This PR makes them 3-10x faster to redraw, by stopping
doing things that are slow :) Part of #126087 thumbnail improvements task.
- No longer do mute semitransparency or corner rounding on the CPU, do it in
shader instead.
- Stop creating a separate GPU texture for each thumbnail, on every repaint,
and drawing each thumbnail as a separate draw call. Instead, put thumbnails
into a single texture atlas (using a simple shelf packing algorithm), and
draw them in batch, passing data via UBO. The atlas is still re-created every
frame, but that does not seem to be a performance issue. Thumbnails are
cropped horizontally based on how much of their parts are visible (e.g. a
narrow strip on screen), so realistically the atlas size is kinda
proportional to screen size, and ends up being just several megabytes of data
transfer between CPU -> GPU each frame.
On this Sprite Fright edit timeline view (612 visible thumbnails), time taken
to repaint the timeline window:
- Mac (M1 Max, Metal): 68.1ms -> 4.7ms
- Windows (Ryzen 5950X, RTX 3080Ti, OpenGL): 23.7ms -> 6.8ms
This also fixes a visual issue with thumbnails, where when strips are very
tall, the "rounded corners" that were poked right into the thumbnail bitmap
on the CPU were showing up due to actual bitmap being scaled up a lot.
Pull Request: https://projects.blender.org/blender/blender/pulls/126972
4c8f22447f