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[Chris Coulson <chris.coulson@xxxxxxxxxxxxx>]

Public bug reported:

In bug 1257721, I made Oxide DPI aware by passing an appropriate device
pixel ratio to Chromium. However, the way this is implemented on Ubuntu
is not really ideal. I expected to be able to read the DPR from
QScreen::devicePixelRatio, but this is always 1.0f on Ubuntu regardless
of the device scale. Instead, device pixel independence is implemented
entirely in ubuntu-ui-toolkit by providing a QML component for
converting between grid units and device pixels, based on an environment
variable called "GRID_UNIT_PX".

For now, I implemented a workaround in Oxide to also set the DPR to
GRID_UNIT_PX / 8 when running with the Ubuntu platform plugin, and
QScreen::devicePixelRatio on all other platforms.

I think that qtubuntu should instead override QScreen::devicePixelRatio
(that could still come from the same environment variable for now), and
ubuntu-ui-toolkit should do the conversion from grid units to device
pixels using this instead.

** Affects: qtubuntu (Ubuntu)
     Importance: Undecided
         Status: New

** Affects: ubuntu-ui-toolkit (Ubuntu)
     Importance: Undecided
         Status: New

** Also affects: ubuntu-ui-toolkit (Ubuntu)
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1275748

Title:
  Ubuntu QPA plugin does not override QScreen::devicePixelRatio

Status in “qtubuntu” package in Ubuntu:
  New
Status in “ubuntu-ui-toolkit” package in Ubuntu:
  New

Bug description:
  In bug 1257721, I made Oxide DPI aware by passing an appropriate
  device pixel ratio to Chromium. However, the way this is implemented
  on Ubuntu is not really ideal. I expected to be able to read the DPR
  from QScreen::devicePixelRatio, but this is always 1.0f on Ubuntu
  regardless of the device scale. Instead, device pixel independence is
  implemented entirely in ubuntu-ui-toolkit by providing a QML component
  for converting between grid units and device pixels, based on an
  environment variable called "GRID_UNIT_PX".

  For now, I implemented a workaround in Oxide to also set the DPR to
  GRID_UNIT_PX / 8 when running with the Ubuntu platform plugin, and
  QScreen::devicePixelRatio on all other platforms.

  I think that qtubuntu should instead override
  QScreen::devicePixelRatio (that could still come from the same
  environment variable for now), and ubuntu-ui-toolkit should do the
  conversion from grid units to device pixels using this instead.

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