SDL2: Support highdpi

[grorp]

Fixes #14549

Tested on Windows. This could work on Mac too, but I don't have a device to test it there.

I used CIrrDeviceSDL from https://github.com/MoNTE48/Irrlicht as a reference, but I believe my implementation is slightly more elegant.

To do

This PR is a Ready for Review.

How to test

Set the display/screen scaling settings on Windows, verify that Minetest respects them. Verify that mouse input works correctly. Also verify that the window size is saved and restored correctly.

[superfloh247]

tested on Mac: everything looks and behaves normal

[grorp]

@superfloh247 in #14268 (comment), you wrote for USE_SDL2=TRUE:

HUD elements and texts are way larger

Does this PR fix that?

[superfloh247]

@superfloh247 in #14268 (comment), you wrote for USE_SDL2=TRUE:

HUD elements and texts are way larger

Does this PR fix that?

you tell me

[grorp]

you tell me

Your old screenshots have a different resolution. With the old screenshots scaled down to 50% to be able to compare, it looks like the issue is fixed. Is it?

[superfloh247]

without patch

[superfloh247]

looks like the font size increases a tiny bit with this patch

[grorp]

looks like the font size increases a tiny bit with this patch

The font size on both screenshots looks the same to me

without patch

I assume the "with patch" screenshot is with USE_SDL2=TRUE. What about the "without patch" screenshot? Is it with USE_SDL2=FALSE?

[superfloh247]

with PR, USE_SDL2=TRUE

with PR, USE_SDL2=FALSE

without PR, USE_SDL2=TRUE

without PR, USE_SDL2=FALSE

you're right, all texts look exactly the same

[grorp]

Ok, thank you for testing. The results don't make much sense for me, but at least nothing is broken.

[sfan5]

doesn't work on my xfce/x11 hidpi system: window and everything else is too small (scale not detected)

[grorp]

Lots of additional information

I had only tested this PR on Windows so far. Now I also tested it on two Linux systems. Here are my results:

	100%	200%
Fedora Linux 40 (Workstation Edition) GNOME 46 X11	window size = 1920x1080 drawable size = 1920x1080 scale = 1; 1 ✔ SDL_GetDisplayDPI() scale = 1.05833;1.05833 ❌	window size = 1920x1080 drawable size = 1920x1080 scale = 1; 1 ❌ SDL_GetDisplayDPI() scale = 1.05833;1.05833 ❌
Fedora Linux 40 (Workstation Edition) GNOME 46 Wayland	window size = 1920x1080 drawable size = 1920x1080 scale = 1; 1 ✔ SDL_GetDisplayDPI() scale = 1.05833;1.05833 ❌	window size = 960x540 drawable size = 1920x1080 scale = 2; 2 ✔ SDL_GetDisplayDPI() scale = 1.05833;1.05833 ❌
Ubuntu 23.10 GNOME 45.2 X11	window size = 1920x1080 drawable size = 1920x1080 scale = 1; 1 ✔ SDL_GetDisplayDPI() scale = 1.47674;1.47294 ❌	window size = 1920x1080 drawable size = 1920x1080 scale = 1; 1 ❌ SDL_GetDisplayDPI() scale = 1.47674;1.47294 ❌
Ubuntu 23.10 GNOME 45.2 Wayland	window size = 1920x1080 drawable size = 1920x1080 scale = 1; 1 ✔ SDL_GetDisplayDPI() scale = 1.49412;1.50395 ❌	window size = 1920x1080 drawable size = 1920x1080 scale = 1; 1 ❌ SDL_GetDisplayDPI() scale = 1.49412;1.50395 ❌

	100% ("fractional scaling")	125% ("fractional scaling")	200% ("fractional scaling")
Fedora Linux 40 (Workstation Edition) GNOME 46 X11	n/a on Fedora	n/a on Fedora	n/a on Fedora
Fedora Linux 40 (Workstation Edition) GNOME 46 Wayland	n/a on Fedora	n/a on Fedora	n/a on Fedora
Ubuntu 23.10 GNOME 45.2 X11	window size = 1920x1080 drawable size = 1920x1080 scale = 1; 1 ✔ SDL_GetDisplayDPI() scale = 1.47674;1.47294 ❌	jumping between two values: window size = 1920x1080 drawable size = 1920x1080 scale = 1; 1 ❌ SDL_GetDisplayDPI() scale = 2.36279;2.3567 ❌ window size = 3072x1728 drawable size = 3072x1728 scale = 1; 1 ❌ SDL_GetDisplayDPI() scale = 2.36279;2.3567 ❌ (downscaled by system => wtf?)	window size = 1920x1080 drawable size = 1920x1080 scale = 1; 1 ❌ SDL_GetDisplayDPI() scale = 1.47674;1.47294 ❌
Ubuntu 23.10 GNOME 45.2 Wayland	window size = 1920x1080 drawable size = 1920x1080 scale = 1; 1 ✔ SDL_GetDisplayDPI() scale = 1.49412;1.50395 ❌	window size = 1536x864 drawable size = 1536x864 scale = 1; 1 ❌ SDL_GetDisplayDPI() scale = 1.19529;1.20316 ❌ (upscaled by system => blurry)	window size = 960x540 drawable size = 960x540 scale = 1; 1 ❌ SDL_GetDisplayDPI() scale = 0.747059;0.751974 ❌ (upscaled by system => blurry)

These are the changes I used: grorp@7f1438f

There are basically two ways to get a scaling factor from SDL2:

1. SDL_GL_GetDrawableSize() / SDL_GetWindowSize() * 96
   => later divided by 96 by Minetest

2. SDL_GetDisplayDPI()
   => later divided by 96 by Minetest

This PR is based on the first approach, which is what the SDL2 docs recommend: https://wiki.libsdl.org/SDL2/SDL_GetDisplayDPI#remarks

Takeaways:

• The only case that works as expected is Fedora/Wayland 200%. That it works on Fedora while it doesn't work on Ubuntu could be because of newer software versions. Or maybe Ubuntu is just broken.

  EDIT: Fedora patches SDL2 to prefer the Wayland video driver by default. When I set SDL_VIDEODRIVER=wayland, scaling works correctly on Ubuntu/Wayland too, including "fractional scaling" without blurriness.

• SDL_GetDisplayDPI returns the "hardware" DPI and doesn't respect user scaling settings.

  On Ubuntu/Wayland/"fractional scaling", user scaling settings are even compensated for: If I set 125%, the window is upscaled by the system and the returned DPI is lowered, so the effective scale would stay exactly the same if we used SDL_GetDisplayDPI for scaling.

  This also means that even on a display that isn't "hidpi", I don't get a scale of 1 when 100% is set. This is a problem for pixel art (see e.g. the loading screen progress bar).

  Looks like SDL_GetDisplayDPI was removed in SDL3: New High DPI functions do not report high DPI screen properly libsdl-org/SDL#9322 (comment), https://github.com/libsdl-org/SDL/blob/f62a1bed161099f734b777ebc38a18d2fb52a8f2/docs/README-highdpi.md

doesn't work on my xfce/x11 hidpi system: window and everything else is too small (scale not detected)

I don't see a way I could improve this PR to make it work better on Linux/X11. It looks like SDL2 simply doesn't support highdpi on X11 (but SDL3 does): libsdl-org/SDL#4176 / libsdl-org/SDL#7718

[grorp]

@superfloh247 it would be great if you could test this PR again. After e0e2f3c, it might actually make a difference on macos (but only if you have a retina/hidpi display).

[superfloh247]

yes it does make a difference
-USE_SDL2=TRUE

do you need any other setting that could influence the fonts?

HUD elements and HUD fonts very small, way too small
other text eg. on signs has normal font size

[grorp]

HUD elements and HUD fonts very small, way too small

Could you test grorp@efbe0d7 and tell me what it outputs to the console after [updateSizeAndScale]?

EDIT: There was a new bug that caused a scale of 0.5 with CIrrDeviceOSX. I've added the fix for that bug to the commit linked above. This shouldn't fix your problem, but if it does, that means you're not compiling with CIrrDeviceSDL.

do you need any other setting that could influence the fonts?

Ideally, you'd test this with the default settings, i.e. an empty minetest.conf file.

Another question: Is there a resolution difference between screenshots taken with Minetest's F12 and screenshots taken with macOS' screenshot feature?

[sfan5]

I don't see a way I could improve this PR to make it work better on Linux/X11. It looks like SDL2 simply doesn't support highdpi on X11 (but SDL3 does)

That's disappointing and actually means a loss of features compares to the older "Linux" device.

[sfan5]

code lgtm

[okias]

I see more and more stuff lacking on X11 (see #14542 Avoid bug on Linux/X11), may I suggest incorporating X11 (and XWayland) deprecation into roadmap? I think there will be more and more problems, as XWayland is (and will be) maintained, but X11 is EOL for some time.

I don't want to cut X11 users, but giving them grace period to migrate (even Xfce working on the transition) is the best thing..

[sfan5]

I don't think that would make much sense as X11 will be with us for at least a few years in the Linux world and there's few signs of the BSD world moving.

[superfloh247]

with this PR and without -USE_SDL2=TRUE

with this PR and with -USE_SDL2=TRUE

latest master without -USE_SDL2=TRUE

latest master with -USE_SDL2=TRUE

the screenshots taken in minetest look exactly the same as the game looks on screen

latest master with -USE_SDL2=TRUE, screenshot taken with OS's snipping tool

[superfloh247]

build.log

[superfloh247]

[superfloh247]

Irrlicht Device: SDL
fonts langer than usual, but very smooth

key binding broken
l-shift does not work to fly down / sneak
l-shift does not work to start commands with / in game mode, only when I open the text console with t, then l-shift works

[grorp]

Seems to work on macOS. Thank you.

The default on macOS is still CIrrDeviceOSX, which doesn't support highdpi. It looks like NSHighResolutionCapable was explicitly set to false by #10970 to fix #10654.

To avoid unexpected behavior changes/regressions with CIrrDeviceOSX, I've reverted the NSHighResolutionCapable change until we switch macOS to CIrrDeviceSDL by default.