High-DPI Qt Fixing Overview

Short Term (5.6.x if possible)

Qt Widgets

QTBUG-36825 StyleSheet background property
QTBUG-47844 [Regression] QLabel scaledContents stretches its pixmap way beyond its size
QTBUG-26795 QGraphicsView: Patch series at: https://codereview.qt-project.org/#/c/142920 . Currently blocked on "QPaintEngine systemClip shared painter fixing": https://codereview.qt-project.org/#/c/142923/
QTBUG-52606 Combobox popup positioning

X11
QTBUG-52318 Qt Assistant UI scaled incorrectly
QTBUG-53416 Wrong device pixel ratio

Windows

• Accessibility: QTBUG-52943

OS X
QTBUG-50251 Mixed-display (retina + non-retina) setup: icons on non-retina display are downscaled.
QTBUG-46803 grabWindow doesn't work with retina and if an area is specified

Qt Quick
QTBUG-37095 Canvas element renders fuzzy on retina displays
QTBUG-50119 AnimatedSprite does not support @2x hires image resolution
QTBUG-50652
QTBUG-52695

Qt Creator
Flash-of-white when changing displays
Font uglyness for Qt Quick content (most likely) when on 1x display with 2x display attached.

General
Documentation: https://codereview.qt-project.org/#/c/150242/
QTBUG-51111: Android screen size.
QTBUG-52137: QWidget grab with HighDPI mode

DONE
QTBUG-34116

Medium / Long Term (5.7/dev)

Improve QtWidgets support for non-integer devicePixelRatios
Render at an integer factor and downscale. For example, 100x100@1.75x : render at 100x100@2x (200x200) and downsample to 175x175. This requires hardware scaling (OpenGL). Prototype using software scaling on OS X: https://codereview.qt-project.org/143819
QTBUG-53160: renderToTexture mode.

qhighdpiscaling_p.h refactor
Clean up and make the to/from nativePixels internal API and implementation more uniform. Change: https://codereview.qt-project.org/#/c/145925/

Windows Style
Can we make it scalable?

Android Style
The android style is already scalable. However we get duplicate scaling when devicePixelRatio high-DPI is enabled.

QtWidgets API
QIcon::pixmpap(QWindow *is cumbersome) (https://codereview.qt-project.org/#/c/156288/)
classes that have setPixmap() should have setIcon() (QLabel)

QTBUG-49820: Icon and Image loading.
QTBUG-55623: QSystemTrayIcon baloon window
QTBUG-51628: Multi-monitor display woes.

Scale Factor Setting Update
QTBUG-53022