perf(ui): check rectangle intersection when looking for covering grids #38500

Problem:
The ui compositor does not use grid_scroll events when a grid other than
the built in msg_grid exists above the scrolled grid, regardless of
whether it actually intersects the scrolled grid anywhere in the
scrolled region.

When another layer exists at a higher zindex, the ui compositor falls
back to composing every line of the scrolled grid. This is especially
evident when using ui2 which creates a floating window that replaces the
built-in msg_grid. Scrolling around with ui2 enabled has poor
performance because the entire grid is recomposed on every scroll
instead of using grid_scroll.

Solution:
Instead of just checking whether another grid exists at a higher zindex
than curgrid, ensure there's a grid above the curgrid that is positioned
over the particular rectangle of interest, which could be a subrectangle
of the whole grid.

Grids above the curgrid that don't intersect there no longer count as
covering the curgrid, and the compositor can continue to use grid_scroll
scroll events. The floating window created for the command line/messages
with ui2 never intersects with the scrolled region of the main window
grid, which allows performant scrolling with it enabled.

0 files changed, 0 insertions, 0 deletions