Fix GTK cairo backends#28451
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With GTK4, the Cairo context we get is always in logical pixels, and is automatically scaled to the right size, without any worry about blurriness. So in that case, we can ignore all scale factor changes, and assume it's always 1. The remaining effect of tracking scale factor changes is to trigger a re-draw, but GTK will send a resize event to go along with it, which will do that for us. Fixes matplotlib#25847 Replaces matplotlib#25861
With GTK3, the Cairo surface we get is for the whole window, which means the automatic size inference from matplotlib#22004 gets the wrong size. For the GtkDrawingArea, the Cairo context is aligned and clipped to the widget, so nothing goes out-of-bounds. However, since the Cairo renderer flips the origin using the height in the calculation (which is, for the window, bigger than the drawing widget), everything is drawn lower than it should.
tacaswell
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QuLogic
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…451-on-v3.9.x Backport PR #28451 on branch v3.9.x (Fix GTK cairo backends)
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PR summary
For GTK4Cairo, HiDPI displays were broken because we were scaling unnecessarily, as GTK4 takes care of setting up the Cairo context for us with the right scale.
For GTK3Cairo, all displays were broken, as we inferred the size from the backing surface (since #22004), which is the size of the window. Then we re-orient the origin using that height, causing everything to be placed incorrectly.
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