Potential client icon distortion under Linux, sometimes

Under Linux, as of Jan 15 2024 on the qt6 branch, there appears to be some icon distortion on some systems, looking like mis-scaling to 51x51 px (from an original icon size of 96x96 px -- expected e.g. 48x48 px?). For example:

image attached icon_distortion_01.png: unscaled screenshot of part of a questionnaire, showing distortion;
..._02.png: zoomed to 400%, showing distortion;
..._03.png: original choose_page.png at same magnification, showing no distortion in original;
..._04.png: original next_page.png at same magnification, showing no distortion in original;
..._05.png: system information reported by CamCOPS at the time.

The icons are being created in QuestionnaireHeader::QuestionnaireHeader() by ImageButton(), with no size specified, so I think it's going via uifunc::getPixmap(). I've not tracked through to remind myself of the full process but there is

// in uiconst.cpp
const Dpi DEFAULT_DPI(96, 96);  // standard for monitors

Dpi g_logical_dpi = DEFAULT_DPI;
Dpi g_physical_dpi = DEFAULT_DPI;

const QSize ICONSIZE_FOR_DEFAULT_DPI(48, 48);

const QSize SMALL_ICONSIZE_FOR_DEFAULT_DPI(48, 48);

QSize g_iconsize = ICONSIZE_FOR_DEFAULT_DPI;

QSize g_small_iconsize = SMALL_ICONSIZE_FOR_DEFAULT_DPI;

etc. – however, forcing physical DPI to 96,96 in settings and restarting doesn't seem to make a visual difference either, and is still scaling to about 51x51. (Scaling to 51 is a bit funny; I'd expect 48 and then I imagine it'd look better.) Maybe it's looking at physical DPI as reported by the OS and not overriding it somewhere.

Not observed elsewhere, even on other Linux systems -- parked for now.

icon_distortion_01 icon_distortion_02 icon_distortion_03 icon_distortion_04 icon_distortion_05

ucam-department-of-psychiatry / camcops

Potential client icon distortion under Linux, sometimes #332