Improve performance of scrollbar marks #16006
Merged
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This replaces the use of a
<Canvas>
with an<Image>
for drawingscrollbar marks. Otherwise, WinUI struggles with the up to ~9000 UI
elements as they get dirtied every time the scrollbar moves.
(FWIW 9000 is not a lot and it should not struggle with that.)
The
<Image>
element has the benefit that we can get hold of a CPU-sidebitmap which we can manually draw our marks into and then swap them into
the UI tree. It draws the same 9000 elements, but now WinUI doesn't
struggle anymore because only 1 element gets invalidated every time.
Closes #15955
Validation Steps Performed