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xwayland: Report correct mode size when rootful

Olivier Fourdan requested to merge ofourdan/xserver:xwayland-fix-vidmode-rootful into master

The vidmode extension emulation in Xwayland reports the modeline based on the current mode.

To do so, it searches for the mode using xwl_output_find_mode(-1, -1) which is supposed to return the current mode, whatever that mode is.

With XRandR emulation, in rootless mode, the default value is the mode at index 0. That assumption, however is not true when running rootful.

That means that the vidmode extension will always return the highest mode available, which is 5120x288, with Xwayland running rootful:

  $ xwayland-run -geometry 1024x768 -- xvidtune -show
  "5120x2880"   1276.50   5120 5560 6128 7136   2880 2883 2888 2982 -hsync +vsync

Luckily, when Xwayland is running rootful, we have the current mode size conveniently stored in dedicated fields of the xwayland output struct, so we can use that to search for the right mode being used and report that through the vidmode extension:

  $ xwayland-run -geometry 1024x768 -- xvidtune -show
  "1024x768"     63.50   1024 1064 1176 1328    768  771  775  798 -hsync +vsync

That fixes several games rendering at the wrong size when running within Xwayland rootful.

Signed-off-by: Olivier Fourdan ofourdan@redhat.com

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