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Commit 0124b1ef authored by Erik Kurzinger's avatar Erik Kurzinger
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[platforms/X11] Disable VSync for QtQuick Windows

Summary:
QtQuick windows created by KWin currently use the default swap interval
of 1, meaning buffer swaps will block until vblank. However, this
results in a problematic interaction on hybrid graphics systems running
the proprietary NVIDIA driver.  VSync on such setups relies on a system
called "PRIME synchronization", where the xf86-video-modesetting driver
controlling the display will signal the NVIDIA driver when vblank has
occurred. The issue is that it will only do so if there has been damage
to the screen.

So, when KWin creates a QtQuick window, compositing will stop waiting on
the window to render, therefore no damage to the screen will occur. But
this means that no vblank notifications will be delivered to the NVIDIA
driver, so the glXSwapBuffers call by the QtQuick window will block
perpetually. The end result is a freeze of the desktop.

To get around this, we can simply disable vsync for QtQuick windows by
setting the swap interval for the de...
parent 105ae7bb
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