Optimization opportunities (tracking issue)

[emilk]

There is a lot of room for improvements to the CPU usage of egui. Here are some things worth investigating:

• Try different hash algorithms for Id, FontCache and others.
• Precompute vertices for circles and rounded corners in epaint::Tessellator constructor (Precompute rounded vertices #1547)
• Paint small filled circles using textured rects (by adding a few low-radius circles to the font atlas) (Optimize tessellation of filled circles #1616)
• Run egui with a proper profiler and see what pops up
  • Try https://github.com/mstange/perfrecord
• Utilizing a Cow like type for RichText / LayoutJob #1098
• eframe/native: run App::update and the rendering in different threads
• Output a single veretex buffer and index buffer instead of Vec<ClippedPrimitive>
• Performance: replace bools in Response with bit-sets #3862
• Optimize Plot egui_plot#18,

Any PR should come with a benchmark.

[emilk]

I added integration with the puffin profiler in #1483 to make it easier to a get a rough overview of app performance.

[YgorSouza]

This could be updated to link to #3862 and emilk/egui_plot#18, which have PRs in progress.