/*******************************************************************************
 * Copyright (c) 2000, 2004 IBM Corporation and others.
 * All rights reserved. This program and the accompanying materials
 * are made available under the terms of the Eclipse Public License v1.0
 * which accompanies this distribution, and is available at
 * http://www.eclipse.org/legal/epl-v10.html
 *
 * Contributors:
 * IBM Corporation - initial API and implementation
 *******************************************************************************/
package org.eclipse.jwt.examples.wizards;

import org.eclipse.swt.SWT;
import org.eclipse.swt.graphics.GC;
import org.eclipse.swt.graphics.Image;
import org.eclipse.swt.graphics.Point;
import org.eclipse.swt.graphics.Rectangle;
import org.eclipse.swt.widgets.Canvas;
import org.eclipse.swt.widgets.Composite;
import org.eclipse.swt.widgets.Event;
import org.eclipse.swt.widgets.Listener;
import org.eclipse.swt.widgets.ScrollBar;


/**
 * A <code>Canvas</code> showing a single centered SWT <code>Image</code>. If the
 * <code>Image</code> is larger than the <code>Canvas<code>,
 * <code>Scrollbars</code> will appear.
 */
// This code comes from org.eclipse.compare.internal
class ImageCanvas
		extends Canvas
{

	private Image fImage;


	/*
	 * Create a new ImageCanvas with the given SWT stylebits. (SWT.H_SCROLL and
	 * SWT.V_SCROLL are automtically added).
	 */
	public ImageCanvas(Composite parent, int style)
	{
		super(parent, style | SWT.H_SCROLL | SWT.V_SCROLL);
		ScrollBar sb = getHorizontalBar();
		sb.setIncrement(20);
		sb.addListener(SWT.Selection, new Listener()
		{

			public void handleEvent(Event e)
			{
				repaint();
			}
		});
		sb = getVerticalBar();
		sb.setIncrement(20);
		sb.addListener(SWT.Selection, new Listener()
		{

			public void handleEvent(Event e)
			{
				repaint();
			}
		});
		addListener(SWT.Resize, new Listener()
		{

			public void handleEvent(Event e)
			{
				updateScrollbars();
			}
		});
		addListener(SWT.Paint, new Listener()
		{

			public void handleEvent(Event event)
			{
				paint(event.gc);
			}
		});
	}


	/*
	 * Set the SWT Image to use as the ImageCanvas contents.
	 */
	public void setImage(Image img)
	{
		fImage = img;
		if (!isDisposed())
		{
			getHorizontalBar().setSelection(0);
			getVerticalBar().setSelection(0);
			updateScrollbars();
			getParent().layout();
			redraw();
		}
	}


	public void repaint()
	{
		if (!isDisposed())
		{
			GC gc = new GC(this);
			paint(gc);
			gc.dispose();
		}
	}


	void paint(GC gc)
	{
		if (fImage != null)
		{
			Rectangle bounds = fImage.getBounds();
			Rectangle clientArea = getClientArea();
			int x;
			if (bounds.width < clientArea.width)
				x = (clientArea.width - bounds.width) / 2;
			else
				x = -getHorizontalBar().getSelection();
			int y;
			if (bounds.height < clientArea.height)
				y = (clientArea.height - bounds.height) / 2;
			else
				y = -getVerticalBar().getSelection();
			gc.drawImage(fImage, x, y);
		}
	}


	/**
	 * @private
	 */
	void updateScrollbars()
	{
		Rectangle bounds = fImage != null ? fImage.getBounds()
				: new Rectangle(0, 0, 0, 0);
		Point size = getSize();
		Rectangle clientArea = getClientArea();
		ScrollBar horizontal = getHorizontalBar();
		if (bounds.width <= clientArea.width)
		{
			horizontal.setVisible(false);
			horizontal.setSelection(0);
		}
		else
		{
			horizontal.setPageIncrement(clientArea.width - horizontal.getIncrement());
			int max = bounds.width + (size.x - clientArea.width);
			horizontal.setMaximum(max);
			horizontal.setThumb(size.x > max ? max : size.x);
			horizontal.setVisible(true);
		}
		ScrollBar vertical = getVerticalBar();
		if (bounds.height <= clientArea.height)
		{
			vertical.setVisible(false);
			vertical.setSelection(0);
		}
		else
		{
			vertical.setPageIncrement(clientArea.height - vertical.getIncrement());
			int max = bounds.height + (size.y - clientArea.height);
			vertical.setMaximum(max);
			vertical.setThumb(size.y > max ? max : size.y);
			vertical.setVisible(true);
		}
	}

}
