selection flicker

[rjkroege]

When text is selected, scrolling is slower. There is obviously too much work being done. I should make it better. In particular, there is no point in redrawing the selected text multiple times.

[rjkroege]

I spent a little bit of time trying to understand the scheduling behaviour between the draw library and devdraw program. It doesn't seem like devdraw has a particularly good way to express the two separate ideas of:

• permit subsequent pixel reads to depend on previous pixel writes
• show on screen at the next vblank all draw operations up to this point in the command stream.

The way that I simplified the selection painting code also overdraws.

[rjkroege]

I have a wip design for a revised Frame drawing path that:

• supports varying text styles #70 (though with devdraw perf limitations)
• eliminates selection flicker
• removes selection overdraw
• works with existing devdraw
• has fewer display bugs (though other than selection flicker, it appears that I've fixed almost all of the Frame bugs now)

[Superpat]

Not sure if it's the same thing, but under OpenBSD 6.4-current, I find Edwood to be noticeably slower than plan9port Acme when playing with selections.

[rjkroege]

Indeed. Fixing that is the point of the bug. I know why this is. I made a simplifying assumption in the implementation of Frame that was regrettable. There are a lot of opportunities to improve the Frame drawing code.

[rjkroege]

Also note several points in the code where I'm redrawing unnecessarily.