ASTScrolledCanvas.java

package ch.hsr.ifs.pasta;

import org.eclipse.swt.custom.ScrolledComposite;
import org.eclipse.swt.events.DragDetectEvent;
import org.eclipse.swt.events.DragDetectListener;
import org.eclipse.swt.events.MouseAdapter;
import org.eclipse.swt.events.MouseEvent;
import org.eclipse.swt.events.MouseMoveListener;
import org.eclipse.swt.graphics.Cursor;
import org.eclipse.swt.graphics.ImageData;
import org.eclipse.swt.graphics.Point;
import org.eclipse.swt.widgets.Canvas;
import org.eclipse.ui.plugin.AbstractUIPlugin;

public class ASTScrolledCanvas extends Canvas {
	private static final int CURSOR_SIZE = 38;

	private Point dragSource = null;
	private boolean dragFlag = false;

	private final ImageData grabImage = AbstractUIPlugin
			.imageDescriptorFromPlugin(PastaPlugin.PLUGIN_ID, "/icons/closedhand.gif").getImageData();
	private final Cursor grabCursor = new Cursor(getDisplay(), grabImage.scaledTo(CURSOR_SIZE, CURSOR_SIZE),
			CURSOR_SIZE / 2,
			CURSOR_SIZE / 4);

	private final ImageData openImage = AbstractUIPlugin
			.imageDescriptorFromPlugin(PastaPlugin.PLUGIN_ID, "/icons/openhand.gif")
			.getImageData();
	private final Cursor openCursor = new Cursor(getDisplay(), openImage.scaledTo(CURSOR_SIZE, CURSOR_SIZE),
			CURSOR_SIZE / 2,
			CURSOR_SIZE / 4);

	ASTScrolledCanvas(final ScrolledComposite parent, final int style) {
		super(parent, style);
		setCursor(openCursor);
		addDragFunctionality();
	}

	@Override
	public ScrolledComposite getParent() {
		return (ScrolledComposite) super.getParent();
	}

	private void addDragFunctionality() {
		addMouseListener(new MouseAdapter() {

			@Override
			public void mouseDown(final MouseEvent e) {
				dragSource = new Point(e.x, e.y);
				setCursor(grabCursor);
			}

			@Override
			public void mouseUp(final MouseEvent e) {
				dragFlag = false;
				dragSource = null;
				setCursor(openCursor);
			}

		});

		addMouseMoveListener(new MouseMoveListener() {

			@Override
			public void mouseMove(final MouseEvent e) {
				if (dragFlag) {
					ASTScrolledCanvas.this.getParent().setOrigin(
							ASTScrolledCanvas.this.getParent().getOrigin().x + (dragSource.x - e.x),
							ASTScrolledCanvas.this.getParent().getOrigin().y + (dragSource.y - e.y));
				}
			}

		});

		addDragDetectListener(new DragDetectListener() {

			@Override
			public void dragDetected(final DragDetectEvent e) {
				dragFlag = true;
			}

		});
	}

}