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LibGUI+WindowServer: Improve window resizing performance

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The old `GUI::Window` resizing behavior created a new backing store for
each resize event (i.e. every visible window size). This caused a lot of
trashing and on my machine, caused up to 25% of CPU time spent in
creating new backing stores.

The new behavior is a bit more sensible:

  * If the window size is shrinking, the backing store is already large
    enough to contain the entire window - so we don't create a new one.

  * If the window size is growing, as soon as the backing store can no
    longer contain the window, it is inflated with a large margin (of an
    arbitrary chosen 64 pixels) in both directions to accommodate some
    leeway in resizing before an even larger backing store is required.

  * When the user stops resizing the window, the backing store is
    resized to the exact dimensions of the window.

For me, this brings the CPU time for creating backing stores down to 0%.
This commit is contained in:
Jelle Raaijmakers 2023-01-11 21:46:14 +01:00 • committed by Andreas Kling
parent 45e85d20b6
commit 634d1e0197
8 changed files with 73 additions and 39 deletions
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4
Userland/Services/WindowServer/Window.h
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@ -242,6 +242,9 @@ public:
m_backing_store_serial = serial;
}
Gfx::IntSize backing_store_visible_size() const { return m_backing_store_visible_size; }
void set_backing_store_visible_size(Gfx::IntSize visible_size) { m_backing_store_visible_size = visible_size; }
void swap_backing_stores()
{
swap(m_backing_store, m_last_backing_store);
@ -434,6 +437,7 @@ private:
bool m_occluded { false };
RefPtr<Gfx::Bitmap> m_backing_store;
RefPtr<Gfx::Bitmap> m_last_backing_store;
Gfx::IntSize m_backing_store_visible_size {};
i32 m_backing_store_serial { -1 };
i32 m_last_backing_store_serial { -1 };
int m_window_id { -1 };