[patch] Add native macOS DPI detection path#263
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Modern macOS has no X11, but GetActualScaleFactor routed macOS into the X11 branch because XDG_SESSION_TYPE is null and matched `null or "x11"`. That P/Invoked libX11.so.6, which does not exist on macOS, throwing DllNotFoundException. Add a macOS branch that reads the main display backing scale via CoreGraphics (CGDisplayModeGetPixelWidth / CGDisplayModeGetWidth), giving 1.0 on standard displays and 2.0 on Retina. Falls back to the standard DPI scale when the display mode is unavailable or CoreGraphics cannot be loaded (for example, a headless host).
The macOS DPI branch was all native CoreGraphics interop that only runs on a Mac with a display, so it registered 0% new-code coverage on the Windows coverage runner and tripped the SonarCloud coverage gate. Extract the pure pixel-to-point scale arithmetic into an internal MacOSBackingScaleToDpi helper and unit-test it (standard, Retina, fractional, zero-width fallback). Mark the thin native wrapper GetMacOSDpiScale with [ExcludeFromCodeCoverage] and a justification, matching the repo's treatment of other C ABI boundary code. Microsoft Code Coverage honors the attribute, removing the unreachable lines from the denominator.
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Problem
On modern macOS there is no X11 (XQuartz is not present by default). But
ForceDpiAware.GetActualScaleFactor()only special-cased Windows, then readXDG_SESSION_TYPEand fell into the X11 branch whenever it wasnull— which it always is on macOS — via thenull or "x11"match. That P/InvokedlibX11.so.6, a Linux-only library absent on macOS, throwingDllNotFoundExceptionand taking the app down on startup DPI detection.Fix
Add a native macOS branch before the X11/Wayland fork.
GetMacOSDpiScale()reads the main display's current mode via CoreGraphics and takes the pixel-width to point-width ratio as the backing scale factor:CGDisplayModeGetPixelWidth / CGDisplayModeGetWidth→1.0on a standard display,2.0on Retina.scale * StandardDpiScale(96).finally(Core Foundation "Copy" ownership rule).StandardDpiScaleon a null mode, zero width, or a missing library/entry point (for example, a headless host), rather than crashing.The CoreGraphics P/Invokes load by full framework path since macOS frameworks are not on the default dylib search path, and they omit
DefaultDllImportSearchPaths(that attribute controls the Windows loader only).OperatingSystem.IsMacOS()is a recognized platform guard, so the native calls stay analyzer-clean, andForceDpiAware.csis already<Compile Remove>d onnet10.0-ios, so there is no Mac Catalyst / iOS overlap.Verification
dotnet buildclean, zero warnings (warnings-as-errors is on).ForceDpiAwaretests: 7/7 pass on Windows, confirming the existing Windows path is unchanged.Not runtime-verified on macOS. The new branch only executes on a Mac and could not be exercised from the Windows dev environment. Manual check on a Mac:
dotnet run --project examples/ImGuiAppDemoshould launch (previously crashed) and scale correctly on a Retina display.🤖 Generated with Claude Code