Deprecating Display#getDPI

Having the scale factor being based on the screen DPI leads to
unexpected result e.g. Image too big/small. Having a screen dpi
independent factor leads to consistent results

Author: ShahzaibIbrahim

bundles/org.eclipse.swt/Eclipse SWT/win32/org/eclipse/swt/graphics/Device.java

@@ -521,7 +521,18 @@ public int getDepth () {
  * @exception SWTException <ul>
  *    <li>ERROR_DEVICE_DISPOSED - if the receiver has been disposed</li>
  * </ul>
+ *
+ * @deprecated <p> This method returns a single global DPI value
+ * that does not reflect per-monitor DPI settings on modern operating systems.
+ * In environments with different scaling factors across monitors, it may provide
+ * a misleading or meaningless result, as it does not correspond to the actual DPI
+ * of any specific monitor.</p>
+ *
+ * <p>Note: While deprecated for general {@code Device} instances like {@code Display},
+ * this method may still be validly used when called on a {@code Printer} instance,
+ * where a single global DPI value is meaningful and expected.</p>
  */
+@Deprecated
 public Point getDPI () {
 	checkDevice ();
 	long hDC = internal_new_GC (null);

examples/org.eclipse.swt.examples/src/org/eclipse/swt/examples/imageanalyzer/ImageAnalyzer.java

@@ -1165,16 +1165,16 @@ void menuPrint() {
 		if (image == null) return;
 
 		try {
+			final int DOTS_PER_INCH = 96;
 			// Ask the user to specify the printer.
 			PrintDialog dialog = new PrintDialog(shell, SWT.NONE);
 			if (printerData != null) dialog.setPrinterData(printerData);
 			printerData = dialog.open();
 			if (printerData == null) return;
 
 			Printer printer = new Printer(printerData);
-			Point screenDPI = display.getDPI();
 			Point printerDPI = printer.getDPI();
-			int scaleFactor = printerDPI.x / screenDPI.x;
+			int scaleFactor = printerDPI.x / DOTS_PER_INCH;
 			Rectangle trim = printer.computeTrim(0, 0, 0, 0);
 			if (printer.startJob(currentName)) {
 				if (printer.startPage()) {

examples/org.eclipse.swt.snippets/src/org/eclipse/swt/snippets/Snippet361.java

@@ -146,6 +146,7 @@ public void getName(AccessibleEvent e) {
 	}
 
 	private static void performPrintAction(final Display display, final Shell shell) {
+		final int DOTS_PER_INCH = 96;
 		Rectangle r = composite.getBounds();
 		Point p = shell.toDisplay(r.x, r.y);
 		org.eclipse.swt.graphics.Image snapshotImage
@@ -159,9 +160,8 @@ private static void performPrintAction(final Display display, final Shell shell)
 		data = dialog.open();
 		if (data != null) {
 			Printer printer = new Printer(data);
-			Point screenDPI = display.getDPI();
 			Point printerDPI = printer.getDPI();
-			int scaleFactor = printerDPI.x / screenDPI.x;
+			int scaleFactor = printerDPI.x / DOTS_PER_INCH;
 			Rectangle trim = printer.computeTrim(0, 0, 0, 0);
 			if (printer.startJob("Print Image")) {
 				ImageData imageData = snapshotImage.getImageData();

examples/org.eclipse.swt.snippets/src/org/eclipse/swt/snippets/Snippet367.java

@@ -185,7 +185,7 @@ public int getGcStyle() {
 
 		createSeparator(shell);
 
-		new Label (shell, SWT.NONE).setText ("5. 50x50 box\n(Display#getDPI(): " + display.getDPI().x + ")");
+		new Label (shell, SWT.NONE).setText ("5. 50x50 box");
 		Label box= new Label (shell, SWT.NONE);
 		box.setBackground(display.getSystemColor(SWT.COLOR_WIDGET_DARK_SHADOW));
 		box.setLayoutData (new GridData (50, 50));

tests/org.eclipse.swt.tests/JUnit Tests/org/eclipse/swt/tests/junit/Test_org_eclipse_swt_widgets_Display.java

@@ -1573,6 +1573,7 @@ public void test_wake() {
 /* custom */
 boolean disposeExecRan;
 
+@SuppressWarnings("deprecation")
 @Test
 public void test_getDPI() {
 	Display display = new Display();