Assign Windows runtime rescaling to Display instead of DPIUtil

Currently, the runtime rescaling of shells/widgets on Windows is tied to
a property in the DPIUtil class. Since that class is internal, the
property can only be set via a VM argument at startup but cannot be
changed or at least retrieved during runtime from outside the SWT
bundle.

This change reduces the DPIUtil property to a global setting that may be
used to set the behavior for a whole application (in particular an SWT
application) but move the actual state handling for runtime rescaling
behavior to the Display class. This allow to retrieve and change the
value directly on the Display, on which also the DPI awareness for the
UI thread is initialized. As a side effect, it improves testability as a
properly configured display can be used instead of changing the global
state of DPIUtil.

Author: HeikoKlare

bundles/org.eclipse.swt/Eclipse SWT Tests/win32/org/eclipse/swt/internal/DPITestUtil.java

@@ -20,7 +20,6 @@
 public abstract class Win32AutoscaleTestBase {
 	protected Display display;
 	protected Shell shell;
-	private boolean autoScaleOnRuntime;
 
 	@BeforeAll
 	public static void assumeIsFittingPlatform() {
@@ -29,9 +28,8 @@ public static void assumeIsFittingPlatform() {
 
 	@BeforeEach
 	public void setUpTest() {
-		autoScaleOnRuntime = DPITestUtil.isAutoScaleOnRuntimeActive();
 		display = Display.getDefault();
-		autoScaleOnRuntime(true);
+		display.setRescalingAtRuntime(true);
 		shell = new Shell(display);
 	}
 
@@ -40,13 +38,7 @@ public void tearDownTest() {
 		if (shell != null) {
 			shell.dispose();
 		}
-		autoScaleOnRuntime(autoScaleOnRuntime);
-	}
-
-	protected void autoScaleOnRuntime (boolean autoScaleOnRuntime) {
-		DPITestUtil.setAutoScaleOnRunTime(autoScaleOnRuntime);
-		// dispose a existing font registry for the default display
-		SWTFontProvider.disposeFontRegistry(display);
+		display.dispose();
 	}
 
 	protected void changeDPIZoom (int nativeZoom) {

bundles/org.eclipse.swt/Eclipse SWT Tests/win32/org/eclipse/swt/internal/Win32AutoscaleTestBase.java

@@ -30,7 +30,7 @@ class ControlWin32Tests extends Win32AutoscaleTestBase {
 
 	@Test
 	public void testScaleFontCorrectlyInAutoScaleSzenario() {
-		assertTrue("Autoscale property is not set to true", DPITestUtil.isAutoScaleOnRuntimeActive());
+		assertTrue("Autoscale property is not set to true", display.isRescalingAtRuntime());
 
 		int scalingFactor = 2;
 		Control control = new Composite(shell, SWT.NONE);
@@ -54,8 +54,8 @@ public void testScaleFontCorrectlyInAutoScaleSzenario() {
 
 	@Test
 	public void testDoNotScaleFontCorrectlyInNoAutoScaleSzenario() {
-		autoScaleOnRuntime(false);
-		assertFalse("Autoscale property is not set to false", DPITestUtil.isAutoScaleOnRuntimeActive());
+		display.setRescalingAtRuntime(false);
+		assertFalse("Autoscale property is not set to false", display.isRescalingAtRuntime());
 
 		int scalingFactor = 2;
 		Control control = new Composite(shell, SWT.NONE);

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

@@ -6832,4 +6832,33 @@ static long windowProc(long id, long sel, long arg0, long arg1, long arg2, long
 static boolean isActivateShellOnForceFocus() {
 	return "true".equals(System.getProperty("org.eclipse.swt.internal.activateShellOnForceFocus", "true")); //$NON-NLS-1$
 }
+
+/**
+ * {@return whether rescaling of shells at runtime when the DPI scaling of a
+ * shell's monitor changes is activated for this device}
+ * <p>
+ * <b>Note:</b> This functionality is only available on Windows. Calling this
+ * method on other operating system will always return false.
+ *
+ * @since 3.127
+ */
+public boolean isRescalingAtRuntime() {
+	return false;
+}
+
+/**
+ * Activates or deactivates rescaling of shells at runtime whenever the DPI
+ * scaling of the shell's monitor changes. This is only safe to call as long as
+ * no shell has been created for this display. When changing the value after a
+ * shell has been created for this display, the effect is undefined.
+ * <p>
+ * <b>Note:</b> This functionality is only available on Windows. Calling this
+ * method on other operating system will have no effect.
+ *
+ * @param activate whether rescaling shall be activated or deactivated
+ * @since 3.127
+ */
+public void setRescalingAtRuntime(boolean activate) {
+	// not implemented for Cocoa
+}
 }

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

@@ -110,10 +110,8 @@ private static enum AutoScaleMethod { AUTO, NEAREST, SMOOTH }
 			}
 		}
 
-		if ("win32".equals(SWT.getPlatform())) {
-			String updateOnRuntimeValue = System.getProperty (SWT_AUTOSCALE_UPDATE_ON_RUNTIME);
-			autoScaleOnRuntime = Boolean.parseBoolean(updateOnRuntimeValue);
-		}
+		String updateOnRuntimeValue = System.getProperty (SWT_AUTOSCALE_UPDATE_ON_RUNTIME);
+		autoScaleOnRuntime = Boolean.parseBoolean(updateOnRuntimeValue);
 	}
 
 /**
@@ -669,10 +667,6 @@ public static boolean isAutoScaleOnRuntimeActive() {
 	return autoScaleOnRuntime;
 }
 
-static boolean setAutoScaleOnRuntimeActive(boolean value) {
-	return autoScaleOnRuntime = value;
-}
-
 /**
  * AutoScale ImageDataProvider.
  */

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

@@ -6266,4 +6266,34 @@ static int _getDeviceZoom (long monitor_num) {
 static boolean isActivateShellOnForceFocus() {
 	return "true".equals(System.getProperty("org.eclipse.swt.internal.activateShellOnForceFocus", "true")); //$NON-NLS-1$
 }
+
+/**
+ * {@return whether rescaling of shells at runtime when the DPI scaling of a
+ * shell's monitor changes is activated for this device}
+ * <p>
+ * <b>Note:</b> This functionality is only available on Windows. Calling this
+ * method on other operating system will always return false.
+ *
+ * @since 3.127
+ */
+public boolean isRescalingAtRuntime() {
+	return false;
+}
+
+/**
+ * Activates or deactivates rescaling of shells at runtime whenever the DPI
+ * scaling of the shell's monitor changes. This is only safe to call as long as
+ * no shell has been created for this display. When changing the value after a
+ * shell has been created for this display, the effect is undefined.
+ * <p>
+ * <b>Note:</b> This functionality is only available on Windows. Calling this
+ * method on other operating system will have no effect.
+ *
+ * @param activate whether rescaling shall be activated or deactivated
+ * @since 3.127
+ */
+public void setRescalingAtRuntime(boolean activate) {
+	// not implemented for GTK
+}
+
 }

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

@@ -16,6 +16,7 @@
 import java.util.*;
 
 import org.eclipse.swt.graphics.*;
+import org.eclipse.swt.widgets.*;
 
 /**
  * This internal class is used to provide and cache fonts scaled for different zoom levels in the win32
@@ -47,7 +48,7 @@ public static void disposeFontRegistry(Device device) {
 	}
 
 	private static SWTFontRegistry newFontRegistry(Device device) {
-		if (DPIUtil.isAutoScaleOnRuntimeActive()) {
+		if (device instanceof Display display && display.isRescalingAtRuntime()) {
 			return new ScalingSWTFontRegistry(device);
 		}
 		return new DefaultSWTFontRegistry(device);

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

@@ -4910,13 +4910,13 @@ LRESULT WM_DPICHANGED (long wParam, long lParam) {
 		event.detail = newNativeZoom;
 		event.doit = true;
 
-		if (DPIUtil.isAutoScaleOnRuntimeActive()) {
+		if (getDisplay().isRescalingAtRuntime()) {
 			DPIUtil.setDeviceZoom (newNativeZoom);
 		}
 
 		notifyListeners(SWT.ZoomChanged, event);
 
-		if (DPIUtil.isAutoScaleOnRuntimeActive()) {
+		if (getDisplay().isRescalingAtRuntime()) {
 			RECT rect = new RECT ();
 			COM.MoveMemory(rect, lParam, RECT.sizeof);
 			this.setBoundsInPixels(rect.left, rect.top, rect.right - rect.left, rect.bottom-rect.top);

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

@@ -138,6 +138,7 @@ public class Display extends Device implements Executor {
 	EventTable eventTable, filterTable;
 	boolean useOwnDC;
 	boolean externalEventLoop; // events are dispatched outside SWT, e.g. TrackPopupMenu or DoDragDrop
+	private boolean rescalingAtRuntime;
 
 	/* Widget Table */
 	private Map<Long, Control> controlByHandle;
@@ -582,28 +583,8 @@ public Display () {
  */
 public Display (DeviceData data) {
 	super (data);
-	initializeProperDPIAwareness();
-}
-
-private void initializeProperDPIAwareness() {
-	if (!DPIUtil.isAutoScaleOnRuntimeActive()) {
-		return;
-	}
-	// Auto scaling on runtime requires DPI awareness mode "Per Monitor V2"
-	boolean perMonitorV2Available = OS.WIN32_BUILD > OS.WIN32_BUILD_WIN10_1809;
-	if (!perMonitorV2Available) {
-		System.err.println(
-				"***WARNING: rescaling at runtime is activated but the OS version does not support required DPI awareness mode PerMonitorV2.");
-		return;
-	}
-
-	boolean alreadyUsesPerMonitorV2 = OS.GetThreadDpiAwarenessContext() == OS.DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2;
-	if (alreadyUsesPerMonitorV2) {
-		return;
-	}
-	long setDpiAwarenessResult = OS.SetThreadDpiAwarenessContext(OS.DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2);
-	if (setDpiAwarenessResult == 0L) {
-		System.err.println("***WARNING: setting DPI awareness to PerMonitorV2 failed.");
+	if (DPIUtil.isAutoScaleOnRuntimeActive()) {
+		setRescalingAtRuntime(true);
 	}
 }
 
@@ -5267,4 +5248,62 @@ static String withCrLf (String string) {
 static boolean isActivateShellOnForceFocus() {
 	return "true".equals(System.getProperty("org.eclipse.swt.internal.activateShellOnForceFocus", "true")); //$NON-NLS-1$
 }
+
+/**
+ * {@return whether rescaling of shells at runtime when the DPI scaling of a
+ * shell's monitor changes is activated for this device}
+ * <p>
+ * <b>Note:</b> This functionality is only available on Windows. Calling this
+ * method on other operating system will always return false.
+ *
+ * @since 3.127
+ */
+public boolean isRescalingAtRuntime() {
+	return rescalingAtRuntime;
+}
+
+/**
+ * Activates or deactivates rescaling of shells at runtime whenever the DPI
+ * scaling of the shell's monitor changes. This is only safe to call as long as
+ * no shell has been created for this display. When changing the value after a
+ * shell has been created for this display, the effect is undefined.
+ * <p>
+ * <b>Note:</b> This functionality is only available on Windows. Calling this
+ * method on other operating system will have no effect.
+ *
+ * @param activate whether rescaling shall be activated or deactivated
+ * @since 3.127
+ */
+public void setRescalingAtRuntime(boolean activate) {
+	rescalingAtRuntime = activate;
+	// dispose a existing font registry for the default display
+	SWTFontProvider.disposeFontRegistry(this);
+	setProperDPIAwareness();
+}
+
+private void setProperDPIAwareness() {
+	long desiredDpiAwareness = OS.DPI_AWARENESS_CONTEXT_SYSTEM_AWARE;
+	if (OS.WIN32_BUILD < OS.WIN32_BUILD_WIN10_1607) {
+		System.err.println("***WARNING: the OS version does not support setting DPI awareness.");
+		return;
+	}
+	if (rescalingAtRuntime) {
+		desiredDpiAwareness = OS.DPI_AWARENESS_CONTEXT_PER_MONITOR_AWARE_V2;
+		// Auto scaling on runtime requires DPI awareness mode "Per Monitor V2"
+		boolean perMonitorV2Available = OS.WIN32_BUILD >= OS.WIN32_BUILD_WIN10_1809;
+		if (!perMonitorV2Available) {
+			System.err.println(
+					"***WARNING: rescaling at runtime is activated but the OS version does not support required DPI awareness mode PerMonitorV2.");
+			return;
+		}
+	}
+	if (desiredDpiAwareness == OS.GetThreadDpiAwarenessContext()) {
+		return;
+	}
+	long setDpiAwarenessResult = OS.SetThreadDpiAwarenessContext(desiredDpiAwareness);
+	if (setDpiAwarenessResult == 0L) {
+		System.err.println("***WARNING: setting DPI awareness failed.");
+	}
+}
+
 }

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

@@ -313,7 +313,7 @@ public Shell (Display display, int style) {
 	createWidget ();
 
 
-	if (DPIUtil.isAutoScaleOnRuntimeActive()) {
+	if (getDisplay().isRescalingAtRuntime()) {
 		addListener(SWT.ZoomChanged, this::handleZoomEvent);
 	}
 }