[Win32] Deactivate monitor-specific scaling if PerMonitorV2 unsupported

For monitor-specific scaling, PerMonitorV2 is set (and required) as DPI
awareness do work properly. By now, even if the DPI awareness was not
successfully set to PerMonitorV2 (which can actually only happen on
Windows Server 2016), monitor-specific scaling will still be enabled.

With this change, if the required DPI awareness for monitor-specific
scaling could not be set, monitor-specific scaling will automatically be
disabled.

Author: HeikoKlare

bundles/org.eclipse.swt/Eclipse SWT Tests/win32/org/eclipse/swt/widgets/DisplayWin32Test.java

@@ -42,7 +42,7 @@ public void monitorSpecificScaling_withCustomDpiAwareness() {
 		try {
 			setMonitorSpecificScaling(true);
 			Display display = Display.getDefault();
-			assertTrue(display.isRescalingAtRuntime());
+			assertFalse(display.isRescalingAtRuntime());
 			assertExpectedDpiAwareness(OS.DPI_AWARENESS_CONTEXT_SYSTEM_AWARE);
 		} finally {
 			System.clearProperty(Win32DPIUtils.CUSTOM_DPI_AWARENESS_PROPERTY);

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/internal/Win32DPIUtils.java

@@ -85,6 +85,10 @@ public static boolean setDPIAwareness(long desiredDpiAwareness) {
 		return true;
 	}
 
+	public static boolean hasProperDpiAwarenessForMonitorSpecificScaling() {
+		return OS.AreDpiAwarenessContextsEqual(OS.DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2, OS.GetThreadDpiAwarenessContext());
+	}
+
 	public static <T> T runWithProperDPIAwareness(Display display, Supplier<T> operation) {
 		if (customDpiAwareness == -1) {
 			return operation.get();

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/widgets/Display.java

@@ -5408,9 +5408,9 @@ private boolean initializeAutoscaling(boolean useMonitorSpecificScaling) {
 	if (!Win32DPIUtils.initializeCustomDpiAwareness() && !DPIUtil.isCustomAutoScale()) {
 		successfullySetDpiAwareness = setDpiAwareness(useMonitorSpecificScaling);
 	}
-	DPIUtil.setMonitorSpecificScaling(useMonitorSpecificScaling);
-	rescalingAtRuntime = useMonitorSpecificScaling;
-	coordinateSystemMapper = useMonitorSpecificScaling ? new MultiZoomCoordinateSystemMapper(this, this::getMonitors) : new SingleZoomCoordinateSystemMapper(this);
+	rescalingAtRuntime = useMonitorSpecificScaling && Win32DPIUtils.hasProperDpiAwarenessForMonitorSpecificScaling();
+	DPIUtil.setMonitorSpecificScaling(rescalingAtRuntime);
+	coordinateSystemMapper = rescalingAtRuntime ? new MultiZoomCoordinateSystemMapper(this, this::getMonitors) : new SingleZoomCoordinateSystemMapper(this);
 	// dispose an existing font registry for the default display
 	SWTFontProvider.disposeFontRegistry(this);
 	return successfullySetDpiAwareness;