Incorrect HiDPI handling on Linux in a Plasma Wayland session #262
Description
Environment
Alchemy Develop 7.2.2.18423219733 (64bit) (SSE4_2)
Release Notes
CPU: Intel(R) Core(TM) Ultra 9 185H (4800 MHz)
Memory: 31447 MB
Concurrency: 22
OS Version: Linux 6.17.1-arch1-1 #1 SMP PREEMPT_DYNAMIC Mon, 06 Oct 2025 18:48:29 +0000 x86_64
Graphics Card Vendor: Intel
Graphics Card: Mesa Intel(R) Arc(tm) Graphics (MTL)
OpenGL Version: 4.6 (Compatibility Profile) Mesa 25.2.4-arch1.1
Window size: 2880x1584
Font Size Adjustment: 96pt
UI Scaling: 1
Draw distance: 128m
Bandwidth: 3000kbit/s
LOD factor: 1.25
Render quality: 2
Texture memory: 0MB
Disk cache: Max size 11468.8 MB (1.6% used)
RestrainedLove API: (disabled)
libcurl Version: libcurl/7.54.1 OpenSSL/1.1.1w zlib/1.3.1.zlib-ng nghttp2/1.66.0
J2C Decoder Version: OpenJPEG Runtime: 2.4.0
Audio Driver Version: FMOD Studio 2.03.09
Dullahan: 1.23.0.202509121212
CEF: 140.1.13+g5eb3258+chromium-140.0.7339.41
Chromium: 140.0.7339.41
LibVLC Version: 3.0.20
Voice Server Version: Not Connected
Compiler Version: GCC 130300
October 13 2025 00:58:17
Description
While testing the develop version I noticed an issue with HiDPI handling. On my notebook I am running a Plasma Wayland session with a display scale of 200%. So on the old Alchemy version I used an UI scaling value of 2.00 while telling Plasma to not scale XWayland applications. On the new version I assume this should be rather handled by the new HiDPI support in SDL3. But out of the box with UI scaling 1.00 I get a result like this:
The fonts are a bit blurry and the overall rendering is very pixelated. So I guess the whole window gets upscaled by a factor of 2 on SDL level, additional to the UI scaling value (200% in plasma + 2.00 in Alchemy gives me a huge UI). Of course setting my display scale to 100% and UI scaling to 2.00 fixes it but that would be very impractical.
Another workaround I tried was setting SDL_VIDEO_WAYLAND_SCALE_TO_DISPLAY=1 which fixes the visual issue. But this makes controlling the movement and camera with my touchpad extremely challenging, I guess because of the internal window scaling. But then it looks like this which was basically what I got in the old version:
Even the size is correct now. But I think Alchemy lacks the "proper DPI awareness" mentioned here, whatever that might be.
Reproduction steps
- Set the display scale in Plasma to 200%
- Set UI Scaling/UI size in Alchemy to 1.00.
I would expect Alchemy to look sharp and honor the scale setting, or ignore the scale setting and only rely on UI size..