Improved HiDPI support - needs testing

[graemeg]

Hi everyone. 👋

I need your help in testing.

I've just pushed a change, that should hopefully improve HiDPI a lot
on X11 systems (Linux & FreeBSD). When I initially implemented DPI
detection (20 years ago), it was the norm to query the physical
monitor dimensions and calculate a DPI from that.

These days, that's very unreliable. So I studied what toolkits like
QT and GTK does. And I've implemented a multi-layered detection
system.

fpGUI now calculates an effective DPI via priority chain, from
top to bottom:

1. FPGUI_SCALE_FACTOR env variable (supports fractions like "1.4")
2. Xft.dpi resource (often set by Gnome, KDE and XFCE desktop environments)
3. QT_SCALE_FACTOR env variable (supports fractions like "1.4")
4. GDK_SCALE env variable (whole numbers only like "1" or "2")
5. Lastly, the physical monitor dimensions as fallback

See commit 706f21d for details.

Any feedback from testing would be greatly appreciated.

ps: I still need to migrate many forms, dialogs etc to MigLayout, and implement SVG icon support, to make the experience even better.

ps No.2: I still need to investigate improvements on Windows and macOS environments as well.

[graemeg]

Windows has also received improvements and support for the FPGUI_SCALE_FACTOR env variable.

[rchastain2]

Hello Graeme.

I have zero knowledge about that topic. I don't know what I could do for testing. I have a cheap laptop, and my desktop is KDE Plasma.

[graemeg]

No worries. 👍 😅

I have a similar problem under Windows. I can test on Linux and FreeBSD, as i have a dual-boot system with access to a 4K monitor. So I could play with the new environment variables support, or simply change the scaling factor or Gnome or KDE Plasma, and any fpGui app should scale accordingly.

My issue is with Windows. I only have access to Windows in a VM, and no way to test HiDPI support there. I did however test the FPGUI_SCALE_FACTOR env variable, and the usual changing of screen DPI to say 120 or so. So those parts I know work at lest. I couldn't test multi-monitors where each monitor has different DPI values. I've added support for that, as per Microsoft API documentation, but no idea if it works. 🤣