performance opportunity with overlay scrollbar
While tracking down some performance issues I noticed one that was completely unexpected.
If we're on fractional-scaling, there is a chance that the damage region for the overlay scrollbar (which is a bit larger than it's visual area) can overlap with the pixel boundary of the window border. That means that we'll hit some slower paths in the compositor.
It was the difference in my getting FPS jank with VTE and not once I dealt with some of the other clipping issues (now that fractional-scaling is on by default).
So that makes me wonder, what if we added another pixel or two of space on the right of the slider, or perhaps tweaked the CSS in such a way that we get just a bit further from the window border to avoid a damage region which overlaps a transparent pixel boundary?
You can see this w/ PAINT_DAMAGE_REGIONS in looking glass and getting oddly sized windows w/ fractional-scaling enabled.