[Win32] Fix cut off controls #2641

In HiDPI scenarios with fractional monitor scales (such as 125% and
175%), some controls appear slightly cut off. The reason for this is
inconsistent rounding of control sizes. The rounding is necessary during
pixel/point conversion and leads to added or lost single pixels. One
controls which obviously shows the behavior is the border of
CTabFolders.

This change adapts the calculation in the following way:
- It ensures that pixelToPoint and pointToPixel conversions for sizes
round in opposite ways instead of rounding up in both directions as
currently done. This ensures that sizes being set (via pointToPixel) are
rounded up while sizes being retrieved (via pixelToPoint) are rounded
down.
- It extracts the pixelToPoint conversion for sizes that are calculated
based on pixel values and are supposed to represent a conservative size
(i.e., better be to high than to low).
- It ensures that also the pixelToPoint conversion of rectangles takes
the proper rounding method for sizes into account.

Fixes #2641

Author: HeikoKlare

bundles/org.eclipse.swt/Eclipse SWT/common/org/eclipse/swt/graphics/RoundingMode.java

@@ -3,7 +3,7 @@
 * @noreference This class is not intended to be referenced by clients
 */
 public enum RoundingMode {
- ROUND, UP;
+ ROUND, UP, DOWN;
 
 public int round(float x) {
 	if (this == ROUND) {
@@ -12,6 +12,9 @@ public int round(float x) {
 	if (this == UP) {
 		return (int) Math.ceil(x);
 	}
+	if (this == DOWN) {
+		return (int) Math.floor(x);
+	}
 	return (int) x;
 }
 }

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

@@ -124,13 +124,17 @@ public static Point pixelToPointAsLocation(Drawable drawable, Point point, int z
 	}
 
 	public static Point pixelToPointAsSize(Point point, int zoom) {
-		return pixelToPoint(point, zoom, RoundingMode.UP);
+		return pixelToPoint(point, zoom, RoundingMode.DOWN);
 	}
 
 	public static Point pixelToPointAsLocation(Point point, int zoom) {
 		return pixelToPoint(point, zoom, RoundingMode.ROUND);
 	}
 
+	public static Point pixelToPointAsConservativeSize(Point point, int zoom) {
+		return pixelToPoint(point, zoom, RoundingMode.UP);
+	}
+
 	private static Point pixelToPoint(Point point, int zoom, RoundingMode mode) {
 		if (zoom == 100 || point == null) return point;
 		Point.OfFloat fPoint = Point.OfFloat.from(point);
@@ -145,7 +149,7 @@ public static Rectangle pixelToPoint(Rectangle rect, int zoom) {
 		if (rect instanceof Rectangle.OfFloat rectOfFloat) return pixelToPoint(rectOfFloat, zoom);
 		Rectangle scaledRect = new Rectangle.OfFloat (0,0,0,0);
 		Point scaledTopLeft = pixelToPointAsLocation(new Point (rect.x, rect.y), zoom);
-		Point scaledBottomRight = pixelToPointAsLocation(new Point (rect.x + rect.width, rect.y + rect.height), zoom);
+		Point scaledBottomRight = pixelToPointAsSize(new Point (rect.x + rect.width, rect.y + rect.height), zoom);
 
 		scaledRect.x = scaledTopLeft.x;
 		scaledRect.y = scaledTopLeft.y;

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

@@ -623,7 +623,7 @@ public Point computeSize (int wHint, int hHint, boolean changed){
 	hHint = (hHint != SWT.DEFAULT ? DPIUtil.pointToPixel(hHint, zoom) : hHint);
 	//We should never return a size that is to small, RoundingMode.UP ensures we at worst case report
 	//a size that is a bit too large by half a point
-	return Win32DPIUtils.pixelToPointAsSize(computeSizeInPixels(wHint, hHint, changed), zoom);
+	return Win32DPIUtils.pixelToPointAsConservativeSize(computeSizeInPixels(wHint, hHint, changed), zoom);
 }
 
 Point computeSizeInPixels (int wHint, int hHint, boolean changed) {

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

@@ -188,7 +188,7 @@ public Point computeSize (int wHint, int hHint) {
 	int zoom = getZoom();
 	wHint = (wHint != SWT.DEFAULT ? DPIUtil.pointToPixel(wHint, zoom) : wHint);
 	hHint = (hHint != SWT.DEFAULT ? DPIUtil.pointToPixel(hHint, zoom) : hHint);
-	return Win32DPIUtils.pixelToPointAsSize(computeSizeInPixels(wHint, hHint), zoom);
+	return Win32DPIUtils.pixelToPointAsConservativeSize(computeSizeInPixels(wHint, hHint), zoom);
 }
 Point computeSizeInPixels (int wHint, int hHint) {
 	int index = parent.indexOf (this);

tests/org.eclipse.swt.tests.win32/JUnit Tests/org/eclipse/swt/tests/win32/Win32DPIUtilTests.java

@@ -103,7 +103,7 @@ public void scaleDownPoint() {
 	@Test
 	public void scaleDownRectangle() {
 		Rectangle valueAt200 = new Rectangle(100, 150, 10, 14);
-		Rectangle valueAt150 = new Rectangle(75, 113, 7, 10);
+		Rectangle valueAt150 = new Rectangle(75, 113, 8, 10);
 		Rectangle valueAt100 = new Rectangle(50, 75, 5, 7);
 
 		Rectangle scaledValue = Win32DPIUtils.pixelToPoint(valueAt200, 200);