[Interest] Pixmap redraw on OS X Retina display zoomed-in 4x?

Till Oliver Knoll till.oliver.knoll at gmail.com
Fri Jan 22 21:38:53 CET 2016



> Am 22.01.2016 um 20:44 schrieb Edward Sutton <edward.sutton at subsite.com>:
> 
> 
>> On Jan 22, 2016, at 1:30 PM, Jason H <jhihn at gmx.com> wrote:
>> 
>> >Look for something called DevicePixelRatio... Also QML Screen attached property/element. It might be a shortcoming in Qt, but you should be able to work around it.
> 
> Thanks Jason.  I have same issue on iOS as well.
> 
> I will Google Qt examples for DevicePixelRatio. I am puzzled why Qt scaling does not occur automatically?  
> 
> Maybe it does automatically scale for QML.  I am using QWidgets.

Just a shot into the blue: at least on OS X have to be made "Retina ready" by setting some property in the Info.plist file, something like "NSHighResolutionCapable" (true). Plus the "principal class" (?) has to be set there as well, as a precondition.

Off course /not/ setting those values should not result in "4x magnified images" on a retina screen. Sounds like Qt thinks it needs to draw the @2x image resources, whereas OS X treats the application as "non-retina capable".

What about plain text (in widgets)? Does it look "retina-like"? Or pixelated (which would indicate that the OS treats the app as "non-retina capable") on the retina screen?

Maybe just some hope: my own QWidget/QGraphicsView based app looks fine, including QGraphicItems in the QGraphicView. Latest Qt 5.5.1 stock binary, El Capitan.

Even moving the app between retina/non-retina screens works as expected: the Qt app redraws itself with the appropriate resolution as soon as more than 50% of the window overlap with the "other" screen.

Cheers,
  Oliver
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