#351 Image rendering differs between Qt5 and Qt6 builds.

[Lockywolf]

The left is Qt6, the right is Qt5. Qt5 is visibly smoother, as if some gaussian smoothing has been applied.
This is only related to rendering though, as when I am exporting a page as an image from the Qt6 version and open it in an image viewer, it looks like the Qt5 version.

[Lockywolf]

You need to open the image in a dedicated tab, because for some reason, SourceForge does not display it properly.

[Lockywolf]

Running QT_ENABLE_HIGHDPI_SCALING=0 ./src/djview works. This is somehow related to setAttribute(Qt::AA_UseHighDpiPixmaps, true); not working in Qt6, but I have almost zero knowledge of Qt, so I have not idea how to fix it, and just doing qputenv( "QT_ENABLE_HIGHDPI_SCALING", "0" ); does not actually work.

UPD: I have inserted that qputenv( "QT_ENABLE_HIGHDPI_SCALING", "0" ); in the main() function, before the QApplication stuff, and it worked. Not sure this is a good solution, but at least it fixes this problem.

[Leon Bottou]

When the Qt6 reports that the screen implements high dpi scaling ("retina"-style displays), djview , djview generates an image with a higher resolution that matches the true number of pixels and uses this by bypassing the high dpi scaling code. This gives a higher quality image.
For me, this works as expected.

The QT_ENABLE_HIGHDPI_SCALING=0 variable disables all this behavior, so that Qt6 matches Qt5's lower quality image. This could be useful to save cycles or memory.