Introduce internal OfFloat classes for better scaling #62

This commit introduces Rectangle.OfFloat and Point.OfFloat classes as an
extension of Rectangle and Point respectively to improve scaling
precision in the DPIUtil by using residuals obtained from rounding.

Contributes to
#62 and
#128

Author: amartya4256

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

@@ -43,7 +43,7 @@
  * @see <a href="http://www.eclipse.org/swt/">Sample code and further information</a>
  */
 
-public sealed class Point implements Serializable permits Point.WithMonitor {
+public sealed class Point implements Serializable permits Point.OfFloat {
 
 	/**
 	 * the x coordinate of the point
@@ -120,14 +120,56 @@ public String toString () {
 
 /**
  * Instances of this class represent {@link org.eclipse.swt.graphics.Point}
+ * objects with the fields capable of storing more precise value in float.
+ *
+ * @since 3.131
+ * @noreference This class is not intended to be referenced by clients
+ */
+public static sealed class OfFloat extends Point permits Point.WithMonitor {
+
+	private static final long serialVersionUID = -1862062276431597053L;
+
+	public float residualX, residualY;
+
+	public OfFloat(int x, int y) {
+		super(x, y);
+	}
+
+	public OfFloat(float x, float y) {
+		super(Math.round(x), Math.round(y));
+		this.residualX = x - this.x;
+		this.residualY = y - this.y;
+	}
+
+	public float getX() {
+		return x + residualX;
+	}
+
+	public float getY() {
+		return y + residualY;
+	}
+
+	public void setX(float x) {
+		this.x = Math.round(x);
+		this.residualX = x - this.x;
+	}
+
+	public void setY(float y) {
+		this.y = Math.round(y);
+		this.residualY = y - this.y;
+	}
+}
+
+/**
+ * Instances of this class represent {@link org.eclipse.swt.graphics.Point.OfFloat}
  * objects along with the context of the monitor in relation to which they are
  * placed on the display. The monitor awareness makes it easy to scale and
  * translate the points between pixels and points.
  *
  * @since 3.131
  * @noreference This class is not intended to be referenced by clients
  */
-public static final class WithMonitor extends Point {
+public static final class WithMonitor extends Point.OfFloat {
 
 	private static final long serialVersionUID = 6077427420686999194L;
 
@@ -155,4 +197,3 @@ public Monitor getMonitor() {
 }
 
 }
-

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

@@ -46,7 +46,7 @@
  * @see <a href="http://www.eclipse.org/swt/">Sample code and further information</a>
  */
 
-public sealed class Rectangle implements Serializable, Cloneable permits Rectangle.WithMonitor {
+public sealed class Rectangle implements Serializable, Cloneable permits Rectangle.OfFloat {
 
 	/**
 	 * the x coordinate of the rectangle
@@ -375,7 +375,7 @@ public Rectangle union (Rectangle rect) {
  */
 public static Rectangle of(Point topLeft, int width, int height) {
 	if (topLeft instanceof Point.WithMonitor monitorAwareTopLeft) {
-		return new Rectangle.WithMonitor(topLeft.x, topLeft.y, width, height, monitorAwareTopLeft.getMonitor());
+		return new Rectangle.WithMonitor(monitorAwareTopLeft.getX(), monitorAwareTopLeft.getY(), width, height, monitorAwareTopLeft.getMonitor());
 	}
 	return new Rectangle(topLeft.x, topLeft.y, width, height);
 }
@@ -400,14 +400,77 @@ public Rectangle clone() {
 
 /**
  * Instances of this class represent {@link org.eclipse.swt.graphics.Rectangle}
+ * objects which supports values of Float type for it's fields
+ *
+ * @since 3.131
+ * @noreference This class is not intended to be referenced by clients
+ */
+public static sealed class OfFloat extends Rectangle permits Rectangle.WithMonitor {
+
+	private static final long serialVersionUID = -3006999002677468391L;
+
+	private float residualX, residualY, residualWidth, residualHeight;
+
+	public OfFloat(int x, int y, int width, int height) {
+		super(x, y, width, height);
+	}
+
+	public OfFloat(float x, float y, float width, float height) {
+		super(Math.round(x), Math.round(y), Math.round(width), Math.round(height));
+		this.residualX = x - this.x;
+		this.residualY = y - this.y;
+		this.residualWidth = width - this.width;
+		this.residualHeight = height - this.height;
+	}
+
+	public float getX() {
+		return x + residualX;
+	}
+
+	public float getY() {
+		return y + residualY;
+	}
+
+	public float getWidth() {
+		return width + residualWidth;
+	}
+
+	public float getHeight() {
+		return height + residualHeight;
+	}
+
+	public void setX(float x) {
+		this.x = Math.round(x);
+		this.residualX = x - this.x;
+	}
+
+	public void setY(float y) {
+		this.y = Math.round(y);
+		this.residualY = y - this.y;
+	}
+
+	public void setWidth(float width) {
+		this.width = Math.round(width);
+		this.residualWidth = width - this.width;
+	}
+
+	public void setHeight(float height) {
+		this.height = Math.round(height);
+		this.residualHeight = height - this.height;
+	}
+
+}
+
+/**
+ * Instances of this class represent {@link org.eclipse.swt.graphics.Rectangle.OfFloat}
  * objects along with the context of the monitor in relation to which they are
  * placed on the display. The monitor awareness makes it easy to scale and
  * translate the rectangles between pixels and points.
  *
  * @since 3.131
  * @noreference This class is not intended to be referenced by clients
  */
-public static final class WithMonitor extends Rectangle {
+public static final class WithMonitor extends Rectangle.OfFloat {
 
 	private static final long serialVersionUID = 5041911840525116925L;
 
@@ -427,6 +490,11 @@ public WithMonitor(int x, int y, int width, int height, Monitor monitor) {
 		this.monitor = monitor;
 	}
 
+	private WithMonitor(float x, float y, float width, float height, Monitor monitor) {
+		super(x, y, width, height);
+		this.monitor = monitor;
+	}
+
 	/**
 	 * {@return the monitor with whose context the instance is created}
 	 */
@@ -436,8 +504,8 @@ public Monitor getMonitor() {
 
 	@Override
 	public Rectangle.WithMonitor clone() {
-		return new Rectangle.WithMonitor(x, y, width, height, monitor);
+		return new Rectangle.WithMonitor(getX(), getY(), getWidth(), getHeight(), monitor);
 	}
 
 }
-}
+}

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

@@ -228,11 +228,11 @@ public static Point autoScaleDown(Point point) {
 
 public static Point scaleDown(Point point, int zoom) {
 	if (zoom == 100 || point == null) return point;
+	Point.OfFloat fPoint = createPrecisionPointFrom(point);
 	float scaleFactor = getScalingFactor(zoom);
-	Point scaledPoint = new Point (0,0);
-	scaledPoint.x = Math.round (point.x / scaleFactor);
-	scaledPoint.y = Math.round (point.y / scaleFactor);
-	return scaledPoint;
+	float scaledX = fPoint.getX() / scaleFactor;
+	float scaledY = fPoint.getY() / scaleFactor;
+	return new Point.OfFloat(scaledX, scaledY);
 }
 
 /**
@@ -255,16 +255,7 @@ public static Rectangle autoScaleDown(Rectangle rect) {
 }
 
 public static Rectangle scaleDown(Rectangle rect, int zoom) {
-	if (zoom == 100 || rect == null) return rect;
-	Rectangle scaledRect = new Rectangle (0,0,0,0);
-	Point scaledTopLeft = scaleDown(new Point (rect.x, rect.y), zoom);
-	Point scaledBottomRight = scaleDown(new Point (rect.x + rect.width, rect.y + rect.height), zoom);
-
-	scaledRect.x = scaledTopLeft.x;
-	scaledRect.y = scaledTopLeft.y;
-	scaledRect.width = scaledBottomRight.x - scaledTopLeft.x;
-	scaledRect.height = scaledBottomRight.y - scaledTopLeft.y;
-	return scaledRect;
+	return scaleBounds(rect, 100, zoom);
 }
 /**
  * Returns a new scaled down Rectangle if enabled for Drawable class.
@@ -333,13 +324,27 @@ public static boolean isSmoothScalingEnabled() {
  */
 public static Rectangle scaleBounds (Rectangle rect, int targetZoom, int currentZoom) {
 	if (rect == null || targetZoom == currentZoom) return rect;
+	Rectangle.OfFloat fRect = createPrecisionRectangleFrom(rect);
 	float scaleFactor = ((float)targetZoom) / (float)currentZoom;
-	Rectangle returnRect = new Rectangle (0,0,0,0);
-	returnRect.x = Math.round (rect.x * scaleFactor);
-	returnRect.y = Math.round (rect.y * scaleFactor);
-	returnRect.width = Math.round (rect.width * scaleFactor);
-	returnRect.height = Math.round (rect.height * scaleFactor);
-	return returnRect;
+	float scaledX = fRect.getX() * scaleFactor;
+	float scaledY = fRect.getY() * scaleFactor;
+	float scaledWidth = fRect.getWidth() * scaleFactor;
+	float scaledHeight = fRect.getHeight() * scaleFactor;
+	return new Rectangle.OfFloat(scaledX, scaledY, scaledWidth, scaledHeight);
+}
+
+private static Rectangle.OfFloat createPrecisionRectangleFrom(Rectangle rectangle) {
+	if (rectangle instanceof Rectangle.OfFloat) {
+		return (Rectangle.OfFloat) rectangle;
+	}
+	return new Rectangle.OfFloat(rectangle.x, rectangle.y, rectangle.width, rectangle.height);
+}
+
+private static Point.OfFloat createPrecisionPointFrom(Point point) {
+	if (point instanceof Point.OfFloat) {
+		return (Point.OfFloat) point;
+	}
+	return new Point.OfFloat(point.x, point.y);
 }
 
 /**
@@ -436,11 +441,11 @@ public static Point autoScaleUp(Point point) {
 
 public static Point scaleUp(Point point, int zoom) {
 	if (zoom == 100 || point == null) return point;
+	Point.OfFloat fPoint = createPrecisionPointFrom(point);
 	float scaleFactor = getScalingFactor(zoom);
-	Point scaledPoint = new Point(0,0);
-	scaledPoint.x = Math.round (point.x * scaleFactor);
-	scaledPoint.y = Math.round (point.y * scaleFactor);
-	return scaledPoint;
+	float scaledX = fPoint.getX() * scaleFactor;
+	float scaledY = fPoint.getY() * scaleFactor;
+	return new Point.OfFloat(scaledX, scaledY);
 }
 
 /**
@@ -463,16 +468,7 @@ public static Rectangle autoScaleUp(Rectangle rect) {
 }
 
 public static Rectangle scaleUp(Rectangle rect, int zoom) {
-	if (zoom == 100 || rect == null) return rect;
-	Rectangle scaledRect = new Rectangle(0,0,0,0);
-	Point scaledTopLeft = scaleUp (new Point(rect.x, rect.y), zoom);
-	Point scaledBottomRight = scaleUp (new Point(rect.x + rect.width, rect.y + rect.height), zoom);
-
-	scaledRect.x = scaledTopLeft.x;
-	scaledRect.y = scaledTopLeft.y;
-	scaledRect.width = scaledBottomRight.x - scaledTopLeft.x;
-	scaledRect.height = scaledBottomRight.y - scaledTopLeft.y;
-	return scaledRect;
+	return scaleBounds(rect, zoom, 100);
 }
 
 /**

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

@@ -319,4 +319,40 @@ public void scaleUpRectangle() {
 		scaledValue = DPIUtil.scaleUp((Device) null, valueAt100, 100);
 		assertSame(valueAt100, scaledValue, "Scaling up Rectangle without zoom change with device failed");
 	}
+
+	@Test
+	public void scaleDownscaleUpRectangleInvertible() {
+		int[] zooms = new int[] {25, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300, 325, 350, 375, 400};
+		for (int zoom1 : zooms) {
+			for (int zoom2 : zooms) {
+				for (int i = 1; i <= 10000; i++) {
+					Rectangle rect = new Rectangle(0, 0, i, i);
+					Rectangle scaleDown = DPIUtil.scaleDown(rect, zoom1);
+					Rectangle scaleUp = DPIUtil.scaleUp(scaleDown, zoom2);
+					scaleDown = DPIUtil.scaleDown(scaleUp, zoom2);
+					scaleUp = DPIUtil.scaleUp(scaleDown, zoom1);
+					assertEquals(rect.width, scaleUp.width);
+					assertEquals(rect.height, scaleUp.height);
+				}
+			}
+		}
+	}
+
+	@Test
+	public void scaleDownscaleUpPointInvertible() {
+		int[] zooms = new int[] {25, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300, 325, 350, 375, 400};
+		for (int zoom1 : zooms) {
+			for (int zoom2 : zooms) {
+				for (int i = 1; i <= 10000; i++) {
+					Point pt = new Point(i, i);
+					Point scaleDown = DPIUtil.scaleDown(pt, zoom1);
+					Point scaleUp = DPIUtil.scaleUp(scaleDown, zoom2);
+					scaleDown = DPIUtil.scaleDown(scaleUp, zoom2);
+					scaleUp = DPIUtil.scaleUp(scaleDown, zoom1);
+					assertEquals(pt.x, scaleUp.x);
+					assertEquals(pt.y, scaleUp.y);
+				}
+			}
+		}
+	}
 }