This is code to detect the current settings for Windows scaling (Display Settings → Scale and layout → Change the size of text, apps, and other items.)

Generally speaking, this is a nightmare to deal with. The solution, starting in Processing 4.0 beta 6 has two parts:

When running from the PDE, pass the --ui-scale parameter to PApplet (see the code for processing.mode.java.Runner) based on what comes back from Toolkit.getScreenResolution().
When running independently, check for that parameter, and if it's not set, launch a tiny helper app that just returns the DPI value.

With those values in hand, the sketch sets the sun.java2d.uiScale to either 1 or 2. Using fractional values produces ugly results. Similarly, we do not set uiScale to 3 when scaling is at 300%. If you want larger sketches, use scale() in your code.

Using AWT

The Toolkit.getScreenResolution() method does what we want, but it's not possible to set the property for sun.java2d.uiScale once AWT calls have been made.

Use a helper application

This is the solution we're using, which feels a little fragile, but it's working. No need to extract files, adds only 8 Kb, if it fails it doesn't bring down the entire app. (See below for downsides with the other approaches.)

This was done by first doing the JNI setup with MSYS2, and then adding a line to the Makefile to just create the tiny .exe.

Use JNI

This was the intended approach, however the result works 3 times in 5, has an immediate segmentation fault another 20% of the time, and the rest of the time just hangs completely until a force quit. If anyone can fix it, let us know.

Used this really helpful tutorial for JNI
- https://www.baeldung.com/jni

Use Cygwin

Install mingw-86_64-gcc-core, mingw-86_64-gcc-g++, make. (Also nano for good measure.) Had to switch to this because MSYS2 always requires msys-2.0.dll, which is > 3 MB to include, and instead, mingw64 uses the widely available msvcrt.dll.

Building the JNI code

See above for final version used… Also, did not use the JNI version because it failed often.

Install MSYS2 from https://www.msys2.org/ via https://www.mingw-w64.org/downloads/#msys2
Within an MSYS shell, run updates and install gcc
```
  pacman -Syu
  pacman -S base-devel gcc
```
To get your Windows PATH to work (i.e. to find Java), you'll probably also need:
```
  MSYS2_PATH_TYPE=inherit
```
Had to edit $JAVA_HOME/include/win32/jni_md.h to modify the definition of jlong
- https://stackoverflow.com/a/51775636
- other approaches for it https://gist.github.com/ssfang/e52c00cd446081cd72a982a2dd8634d4#file-readme-md (section under “jni with cygwin gcc”)
To cross compile on macOS, use:
```
  brew install mingw-w64
```
This installs g++ as x86_64-w64-mingw32-g++.

Did not use this approach because it would require Windows testing anyway, so it has limited utility.

A link to the formula: https://formulae.brew.sh/formula/mingw-w64

Windows Reference

Resources for the necessary API calls on Windows

GetDeviceCaps function (wingdi.h)
- https://docs.microsoft.com/en-us/windows/win32/api/wingdi/nf-wingdi-getdevicecaps
DPI-related APIs and registry settings
- https://docs.microsoft.com/en-us/windows-hardware/manufacture/desktop/dpi-related-apis-and-registry-settings
Browse code samples for “dpi”
- https://docs.microsoft.com/en-us/samples/browse/?redirectedfrom=TechNet-Gallery&terms=dpi

The code boils down to:

hdc = GetDC(NULL);
horizontalDPI = GetDeviceCaps(hdc, LOGPIXELSX);
verticalDPI = GetDeviceCaps(hdc, LOGPIXELSY);

Use JNA

This is a fairly clean approach with a couple major downsides. One is adding 3 MB of JARs to each application. That is larger than all of processing.core, but you could make an argument that core is already large because of JOGL.

The more serious problems are:

Unpacking the native libraries for JNA on Windows is notoriously finicky. It can kick off the virus checker with unpredictable results—either refusing to run, or delaying startup by a full 60 seconds, or other confusing behaviors.
JNA version conflicts are a nightmare. If JNA is used by the sketch, or a library it depends on, you'll have a major headache on your hands.

That said, this approach is possible. Here's working code:

import com.sun.jna.platform.win32.GDI32;
import com.sun.jna.platform.win32.User32;
import com.sun.jna.platform.win32.WinDef;

WinDef.HDC desktopDc = User32.INSTANCE.GetDC(null);

// if we want to add error handling later
//if (desktopDc == null) {
//  throw new Win32Exception(Native.getLastError());

//INT horizontalDPI = GetDeviceCaps(desktopDc, LOGPIXELSX);
//INT verticalDPI = GetDeviceCaps(desktopDc, LOGPIXELSY);
int x = GDI32.INSTANCE.GetDeviceCaps(desktopDc, 88);
int y = GDI32.INSTANCE.GetDeviceCaps(desktopDc, 90);
println(x, y);
println("scaling: " + x / 96f);

Constants were pulled from https://github.com/tpn/winsdk-7/blob/master/v7.1A/Include/WinGDI.h

#define LOGPIXELSX    88    /* Logical pixels/inch in X                 */
#define LOGPIXELSY    90    /* Logical pixels/inch in Y                 */

Based in part on this gist, but rewritten to use the default device rather than first creating a device.

Use a Registry Key

This would be a simple method to make a single command line call to reg query or similar, but was unable to find a suitable property that was reliable enough.

It's also possible that calling reg query would kick off User Access Control headaches, but that was not confirmed.

reg query reference
- https://docs.microsoft.com/en-us/windows-server/administration/windows-commands/reg-query
returns 0xC0 (192, or 200%) on my machine even though it's set at 225%
- Reg Query "HKCU\Control Panel\Desktop" /v LogPixels
- though looking at this now, if this is gonna return 1x or 2x, it could be an option
iterating through monitors
- HKEY_LOCAL_MACHINE\System\CurrentControlSet\Control\GraphicsDrivers\ScaleFactors\%MonitorID%
- HKEY_CURRENT_USER\Control Panel\Desktop\PerMonitorSettings\%MonitorID%
how to set the dpi scale (includes iterating through monitors)
- https://gist.github.com/itsho/cc4f0c66d3283a6b54582fde31b70a26
DPI-related APIs and registry settings
- https://docs.microsoft.com/en-us/windows-hardware/manufacture/desktop/dpi-related-apis-and-registry-settings?view=windows-11

keys from HKEY_CURRENT_USER\Control Panel\Desktop

  ActiveWndTrackTimeout    REG_DWORD    0x0
  BlockSendInputResets    REG_SZ    0
  CaretTimeout    REG_DWORD    0x1388
  CaretWidth    REG_DWORD    0x1
  ClickLockTime    REG_DWORD    0x4b0
  CoolSwitchColumns    REG_SZ    7
  CoolSwitchRows    REG_SZ    3
  CursorBlinkRate    REG_SZ    530
  DockMoving    REG_SZ    1
  DragFromMaximize    REG_SZ    1
  DragFullWindows    REG_SZ    1
  DragHeight    REG_SZ    4
  DragWidth    REG_SZ    4
  FocusBorderHeight    REG_DWORD    0x1
  FocusBorderWidth    REG_DWORD    0x1
  FontSmoothing    REG_SZ    2
  FontSmoothingGamma    REG_DWORD    0x0
  FontSmoothingOrientation    REG_DWORD    0x1
  FontSmoothingType    REG_DWORD    0x2
  ForegroundFlashCount    REG_DWORD    0x7
  ForegroundLockTimeout    REG_DWORD    0x30d40
  LeftOverlapChars    REG_SZ    3
  MenuShowDelay    REG_SZ    400
  MouseWheelRouting    REG_DWORD    0x2
  PaintDesktopVersion    REG_DWORD    0x0
  Pattern    REG_DWORD    0x0
  RightOverlapChars    REG_SZ    3
  ScreenSaveActive    REG_SZ    1
  SnapSizing    REG_SZ    1
  TileWallpaper    REG_SZ    0
  WallpaperOriginX    REG_DWORD    0x0
  WallpaperOriginY    REG_DWORD    0x0
  WallpaperStyle    REG_SZ    10
  WheelScrollChars    REG_SZ    3
  WheelScrollLines    REG_SZ    3
  WindowArrangementActive    REG_SZ    1
  WallPaper    REG_SZ
  Win8DpiScaling    REG_DWORD    0x0
  DpiScalingVer    REG_DWORD    0x1000
  UserPreferencesMask    REG_BINARY    9E1E078012000000
  MaxVirtualDesktopDimension    REG_DWORD    0xa00
  MaxMonitorDimension    REG_DWORD    0xa00
  TranscodedImageCount    REG_DWORD    0x1
  LastUpdated    REG_DWORD    0xffffffff
  TranscodedImageCache    REG_BINARY    7AC301000A...0000000000 (800 bytes)
  LogPixels    REG_DWORD    0xc0

  HKEY_CURRENT_USER\Control Panel\Desktop\Colors
  HKEY_CURRENT_USER\Control Panel\Desktop\LanguageConfiguration
  HKEY_CURRENT_USER\Control Panel\Desktop\PerMonitorSettings
  HKEY_CURRENT_USER\Control Panel\Desktop\WindowMetrics
  HKEY_CURRENT_USER\Control Panel\Desktop\MuiCached

Other Resources

A longer explanation of some of the issues in play that might be helpful for someone, though I didn't use it:
- https://mariusbancila.ro/blog/2021/05/19/how-to-build-high-dpi-aware-native-desktop-applications/