Limit autoscale mode to quarter and exact only

swt applications will be limited to use autoscale modes quarter and
exact only otherwise user will see an error message stating the
incompatibility. Also the tests testing other autoscale values have been
removed.

Author: ShahzaibIbrahim

bundles/org.eclipse.swt/Eclipse SWT Tests/win32/org/eclipse/swt/widgets/ControlWin32Tests.java

@@ -111,7 +111,7 @@ public void testCorrectScaleUpUsingDifferentSetBoundsMethod() {
 	}
 
 	@ParameterizedTest
-	@CsvSource({ "0.5, 100, true", "1.0, 200, true", "2.0, 200, true", "2.0, quarter, true", "0.5, 100, false",
+	@CsvSource({ "2.0, quarter, true", "0.5, 100, false",
 			"1.0, 200, false", "2.0, 200, false", "2.0, quarter, false", })
 	public void testAutoScaleImageData(float scaleFactor, String autoScale, boolean monitorSpecificScaling) {
 		Win32DPIUtils.setMonitorSpecificScaling(monitorSpecificScaling);

bundles/org.eclipse.swt/Eclipse SWT/common/org/eclipse/swt/internal/DPIUtil.java

@@ -34,6 +34,14 @@ public class DPIUtil {
 	private static int deviceZoom = 100;
 	private static int nativeDeviceZoom = 100;
 
+	/**
+	 * System property that enforces to use autoScale value despite incompatibility
+	 * For e.g. Monitor-specific scaling with int200 autoscale value
+	 */
+	private static final String SWT_AUTOSCALE_DISABLE_COMPATIBILITY_CHECK = "swt.autoScale.force";
+
+	private static final Set<String> ALLOWED_AUTOSCALE_VALUES_FOR_UPDATE_ON_RUNTIME = Set.of("quarter", "exact");
+
 	private static enum AutoScaleMethod { AUTO, NEAREST, SMOOTH;
 
 		public static Optional<AutoScaleMethod> forString(String s) {
@@ -114,6 +122,34 @@ static void setAutoScaleValue(String autoScaleValueArg) {
 	autoScaleValue = autoScaleValueArg;
 }
 
+/**
+ * Returns {@code true} only if the current setup is compatible
+ * with monitor-specific scaling. Returns {@code false} if:
+ * <ul>
+ *   <li>Not running on Windows</li>
+ *   <li>The current auto-scale mode is incompatible</li>
+ * </ul>
+ *
+ * <p>Allowed values: {@code quarter}, {@code exact}.
+ *
+ */
+public static boolean isSetupCompatibleToMonitorSpecificScaling() {
+    // Per-monitor DPI supported only on Windows
+    if (!"win32".equals(SWT.getPlatform())) {
+        return false;
+    }
+
+    // Default means: treat as "quarter" (compatible)
+    if (autoScaleValue == null || "true".equalsIgnoreCase(System.getProperty(SWT_AUTOSCALE_DISABLE_COMPATIBILITY_CHECK))) {
+        return true;
+    }
+
+    String value = autoScaleValue.toLowerCase(Locale.ROOT);
+
+    // Compatible only if one of the known values
+    return ALLOWED_AUTOSCALE_VALUES_FOR_UPDATE_ON_RUNTIME.contains(value);
+}
+
 public static boolean isMonitorSpecificScalingActive() {
 	boolean updateOnRuntimeValue = Boolean.getBoolean (DPIUtil.SWT_AUTOSCALE_UPDATE_ON_RUNTIME);
 	return updateOnRuntimeValue;

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

@@ -270,44 +270,13 @@ public static void setAutoScaleForMonitorSpecificScaling() {
 		boolean isDefaultAutoScale = DPIUtil.getAutoScaleValue() == null;
 		if (isDefaultAutoScale) {
 			DPIUtil.setAutoScaleValue("quarter");
-		} else if (!isSupportedAutoScaleForMonitorSpecificScaling()) {
+		} else if (!DPIUtil.isSetupCompatibleToMonitorSpecificScaling()) {
 			throw new SWTError(SWT.ERROR_NOT_IMPLEMENTED,
 					"monitor-specific scaling is only implemented for auto-scale values \"quarter\", \"exact\", \"false\" or a concrete zoom value, but \""
 							+ DPIUtil.getAutoScaleValue() + "\" has been specified");
 		}
 	}
 
-	/**
-	 * Monitor-specific scaling on Windows only supports auto-scale modes in which
-	 * all elements (font, images, control bounds etc.) are scaled equally or almost
-	 * equally. The previously default mode "integer"/"integer200", which rounded
-	 * the scale factor for everything but fonts to multiples of 100, is complex and
-	 * difficult to realize with monitor-specific rescaling of UI elements. Since a
-	 * uniform scale factor for everything should perspectively be used anyway,
-	 * there will be support for complex auto-scale modes for monitor-specific
-	 * scaling.
-	 *
-	 * The supported modes are "quarter" and "exact" or explicit zoom values given
-	 * by the value itself or "false". Every other value will be treated as
-	 * "integer"/"integer200" and is thus not supported.
-	 */
-	private static boolean isSupportedAutoScaleForMonitorSpecificScaling() {
-		if (DPIUtil.getAutoScaleValue() == null) {
-			return false;
-		}
-		switch (DPIUtil.getAutoScaleValue().toLowerCase()) {
-			case "false", "quarter", "exact": return true;
-		}
-		try {
-			Integer.parseInt(DPIUtil.getAutoScaleValue());
-			return true;
-		} catch (NumberFormatException e) {
-			// unsupported value, use default
-		}
-		return false;
-	}
-
-
 	public static int getPrimaryMonitorZoomAtStartup() {
 		long hDC = OS.GetDC(0);
 		int dpi = OS.GetDeviceCaps(hDC, OS.LOGPIXELSX);