Create custom cursor for 100%, 150% and 200% zoom #872

At least on Windows and Linux, the operating system doesn't seem to
linearly scale the system cursor.

Instead, predefined cursor images are used for:

- ( ..., 150%) - Cursor at 100% monitor zoom
- [150%, 200%) - Cursor at 150% monitor zoom
- (200%,  ...) - Cursor at 200% monitor zoom

SWT is linearly scaling the cursor icon. So if at e.g. 125% zoom, the
cursor inside the widget will be scaled to 125% zoom but is not scaled
outside the widget.

To account for this, the SWT-based cursor is replaced with three cursor
SVGs, one for each of those zoom levels. Note that the images are split
up to make sure the line width is exactly one for each cursor.

Closes #872

Author: ptziegler

org.eclipse.gef/src/org/eclipse/gef/internal/InternalCursor.java

@@ -13,22 +13,10 @@
 
 package org.eclipse.gef.internal;
 
-import java.util.HashMap;
-import java.util.Map;
 import java.util.Objects;
 
-import org.eclipse.swt.SWT;
-import org.eclipse.swt.graphics.GC;
-import org.eclipse.swt.graphics.Image;
-import org.eclipse.swt.graphics.ImageData;
-import org.eclipse.swt.graphics.PaletteData;
-import org.eclipse.swt.graphics.Path;
-import org.eclipse.swt.widgets.Display;
-
 import org.eclipse.jface.resource.ImageDescriptor;
 
-import org.eclipse.draw2d.ColorConstants;
-
 /**
  * This class defines the shape of the default GEF-cursor used for the plug/tree
  * images. The cursor can't be part of the SVG itself, as it is a)
@@ -37,90 +25,26 @@
  * always has a stroke-width of 1px.
  */
 public class InternalCursor {
-	/**
-	 * Defines the shape of the cursor at 100% zoom.
-	 */
-	//@formatter:off
-	private static final float[] CURSOR_POINTS = {
-			 0f,  0f,
-			 0f, 17f,
-			 4f, 13f,
-			 7f, 19f,
-			 9f, 18f,
-			 7f, 13f,
-			 7f, 12f,
-			12f, 12f,
-			 0f,  0f
-	};
-	//@formatter:on
 	/**
 	 * Local cache to store the cursor data for each zoom level.
 	 */
-	private static final Map<Integer, ImageData> CURSOR_AT_ZOOM = new HashMap<>();
+	private static final ImageDescriptor CURSOR_AT_100_ZOOM = InternalImages.createDescriptor("icons/[email protected]"); //$NON-NLS-1$
+	private static final ImageDescriptor CURSOR_AT_150_ZOOM = InternalImages.createDescriptor("icons/[email protected]"); //$NON-NLS-1$
+	private static final ImageDescriptor CURSOR_AT_200_ZOOM = InternalImages.createDescriptor("icons/[email protected]"); //$NON-NLS-1$
 	/**
 	 * The default cursor that is constructed using {link {@link #CURSOR_POINTS}.
 	 * May be replaced with a custom cursor by calling
 	 * {@link #setCursorDescriptor(ImageDescriptor)}.
 	 */
-	private static ImageDescriptor CURRENT_CURSOR_DESCRIPTOR = ImageDescriptor
-			.createFromImageDataProvider(zoom -> CURSOR_AT_ZOOM.computeIfAbsent(zoom, InternalCursor::getCursorAtZoom));
-
-	/**
-	 * This method generates the image data for the cursor at the given zoom level.
-	 * The points defined with {@link #CURSOR_POINTS} are scaled by the given zoom
-	 * and painted onto an image.
-	 *
-	 * @param zoom The zoom level. e.g. 100, 125, 200
-	 * @return The cursor image data at the given zoom level.
-	 */
-	private static ImageData getCursorAtZoom(int zoom) {
-		float maxWidth = 0f;
-		float maxHeight = 0f;
-
-		for (int i = 0; i < CURSOR_POINTS.length; i += 2) {
-			maxWidth = Math.max(maxWidth, CURSOR_POINTS[i]);
-			maxHeight = Math.max(maxHeight, CURSOR_POINTS[i + 1]);
+	private static ImageDescriptor CURRENT_CURSOR_DESCRIPTOR = ImageDescriptor.createFromImageDataProvider(zoom -> {
+		if (zoom < 150) {
+			return CURSOR_AT_100_ZOOM.getImageData(100);
 		}
-
-		float zoomFactor = zoom / 100.0f;
-
-		int width = 1 + (int) Math.ceil(zoomFactor * maxWidth);
-		int height = 1 + (int) Math.ceil(zoomFactor * maxHeight);
-
-		//
-		Display display = Display.getDefault();
-		// Construct path
-		Path path = new Path(display);
-		for (int i = 0; i < CURSOR_POINTS.length; i += 2) {
-			float x = zoomFactor * CURSOR_POINTS[i];
-			float y = zoomFactor * CURSOR_POINTS[i + 1];
-			if (i == 0) {
-				path.moveTo(x, y);
-			} else {
-				path.lineTo(x, y);
-			}
+		if (zoom < 200) {
+			return CURSOR_AT_150_ZOOM.getImageData(100);
 		}
-		// Construct image
-		ImageData imageData = new ImageData(width, height, 32, new PaletteData(0xFF0000, 0x00FF00, 0x0000FF));
-		imageData.alphaData = new byte[width * height];
-		Image image = new Image(display, imageData);
-		GC gc = new GC(image);
-		gc.setAlpha(0);
-		gc.fillRectangle(0, 0, width, height);
-		gc.setAlpha(255);
-		gc.setAntialias(SWT.ON);
-		gc.setLineWidth(1);
-		gc.setBackground(ColorConstants.white);
-		gc.fillPath(path);
-		gc.setBackground(ColorConstants.black);
-		gc.drawPath(path);
-		gc.dispose();
-		path.dispose();
-		// Image is already scaled to expected zoom level
-		imageData = image.getImageData(100);
-		image.dispose();
-		return imageData;
-	}
+		return CURSOR_AT_200_ZOOM.getImageData(100);
+	});
 
 	/**
 	 * Returns the image descriptor for the GEF cursor. Never {@code null}.

org.eclipse.gef/src/org/eclipse/gef/internal/InternalGEFPlugin.java

@@ -127,9 +127,18 @@ public static ImageData scaledImageData(ImageDescriptor descriptor, int zoom) {
 	 */
 	public static Cursor createCursor(ImageDescriptor source, int hotspotX, int hotspotY) {
 		try {
+			ImageDataProvider provider = zoom -> {
+				if (zoom < 150) {
+					return source.getImageData(100);
+				}
+				if (zoom < 200) {
+					return source.getImageData(150);
+				}
+				return source.getImageData(200);
+			};
 			Constructor<Cursor> ctor = Cursor.class.getConstructor(Device.class, ImageDataProvider.class, int.class,
 					int.class);
-			return ctor.newInstance(null, (ImageDataProvider) source::getImageData, hotspotX, hotspotY);
+			return ctor.newInstance(null, provider, hotspotX, hotspotY);
 		} catch (NoSuchMethodException e) {
 			// SWT version < 3.131.0 (no ImageDataProvider-based constructor)
 			return new Cursor(null, source.getImageData(100), hotspotX, hotspotY); // older constructor