fieldassistcolors.java

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/*******************************************************************************
 * Copyright (c) 2006 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.jface.fieldassist;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

import org.eclipse.jface.resource.JFaceColors;
import org.eclipse.swt.SWT;
import org.eclipse.swt.graphics.Color;
import org.eclipse.swt.graphics.RGB;
import org.eclipse.swt.widgets.Control;
import org.eclipse.swt.widgets.Display;

/**
 * FieldAssistColors defines protocol for retrieving colors that can be used to
 * provide visual cues with fields. For consistency with JFace dialogs and
 * wizards, it is recommended that FieldAssistColors is used when colors are
 * used to annotate fields.
 * <p>
 * Color resources that are returned using methods in this class are maintained
 * in the JFace color registries, or by SWT. Users of any color resources
 * provided by this class are not responsible for the lifecycle of the color.
 * Colors provided by this class should never be disposed by clients. In some
 * cases, clients are provided information, such as RGB values, in order to
 * create their own color resources. In these cases, the client should manage
 * the lifecycle of any created resource.
 * 
 * @since 3.2
 */
public class FieldAssistColors {

	private static boolean DEBUG = false;

	/*
	 * Keys are background colors, values are the color with the alpha value
	 * applied
	 */
	private static Map requiredFieldColorMap = new HashMap();

	/*
	 * Keys are colors we have created, values are the displays on which they
	 * were created.
	 */
	private static Map displays = new HashMap();

	/**
	 * Compute the RGB of the color that should be used for the background of a
	 * control to indicate that the control has an error. Because the color
	 * suitable for indicating an error depends on the colors set into the
	 * control, this color is always computed dynamically and provided as an RGB
	 * value. Clients who use this RGB to create a Color resource are
	 * responsible for managing the life cycle of the color.
	 * <p>
	 * This color is computed dynamically each time that it is queried. Clients
	 * should typically call this method once, create a color from the RGB
	 * provided, and dispose of the color when finished using it.
	 * 
	 * @param control
	 *            the control for which the background color should be computed.
	 * @return the RGB value indicating a background color appropriate for
	 *         indicating an error in the control.
	 */
	public static RGB computeErrorFieldBackgroundRGB(Control control) {
		/*
		 * Use a 10% alpha of the error color applied on top of the widget
		 * background color.
		 */
		Color dest = control.getBackground();
		Color src = JFaceColors.getErrorText(control.getDisplay());
		int destRed = dest.getRed();
		int destGreen = dest.getGreen();
		int destBlue = dest.getBlue();

		// 10% alpha
		int alpha = (int) (0xFF * 0.10f);
		// Alpha blending math
		destRed += (src.getRed() - destRed) * alpha / 0xFF;
		destGreen += (src.getGreen() - destGreen) * alpha / 0xFF;
		destBlue += (src.getBlue() - destBlue) * alpha / 0xFF;

		return new RGB(destRed, destGreen, destBlue);
	}

	/**
	 * Return the color that should be used for the background of a control to
	 * indicate that the control is a required field and does not have content.
	 * <p>
	 * This color is managed by FieldAssistResources and should never be
	 * disposed by clients.
	 * 
	 * @param control
	 *            the control on which the background color will be used.
	 * @return the color used to indicate that a field is required.
	 */
	public static Color getRequiredFieldBackgroundColor(Control control) {
		final Display display = control.getDisplay();

		// If we are in high contrast mode, then don't apply an alpha
		if (display.getHighContrast()) {
			return control.getBackground();
		}

		// See if a color has already been computed
		Object storedColor = requiredFieldColorMap.get(control.getBackground());
		if (storedColor != null) {
			return (Color) storedColor;
		}

		// There is no color already created, so we must create one.
		// Use a 15% alpha of yellow on top of the widget background.
		Color dest = control.getBackground();
		Color src = display.getSystemColor(SWT.COLOR_YELLOW);
		int destRed = dest.getRed();
		int destGreen = dest.getGreen();
		int destBlue = dest.getBlue();

		// 15% alpha
		int alpha = (int) (0xFF * 0.15f);
		// Alpha blending math
		destRed += (src.getRed() - destRed) * alpha / 0xFF;
		destGreen += (src.getGreen() - destGreen) * alpha / 0xFF;
		destBlue += (src.getBlue() - destBlue) * alpha / 0xFF;

		// create the color
		Color color = new Color(display, destRed, destGreen, destBlue);
		// record the color in a map using the original color as the key
		requiredFieldColorMap.put(dest, color);
		// If we have never created a color on this display before, install
		// a dispose exec on the display.
		if (!displays.containsValue(display)) {
			display.disposeExec(new Runnable() {
				public void run() {
					disposeColors(display);
				}
			});
		}
		// Record the color and its display in a map for later disposal.
		displays.put(color, display);
		return color;
	}

	/*
	 * Dispose any colors that were allocated for the given display.
	 */
	private static void disposeColors(Display display) {
		List toBeRemoved = new ArrayList(1);

		if (DEBUG) {
			System.out.println("Display map is " + displays.toString()); //$NON-NLS-1$
			System.out.println("Color map is " + requiredFieldColorMap.toString()); //$NON-NLS-1$
		}

		// Look for any stored colors that were created on this display
		for (Iterator i = displays.keySet().iterator(); i.hasNext();) {
			Color color = (Color) i.next();
			if (((Display) displays.get(color)).equals(display)) {
				// The color is on this display. Mark it for removal.
				toBeRemoved.add(color);

				// Now look for any references to it in the required field color
				// map
				List toBeRemovedFromRequiredMap = new ArrayList(1);
				for (Iterator iter = requiredFieldColorMap.keySet().iterator(); iter
						.hasNext();) {
					Color bgColor = (Color) iter.next();
					if (((Color) requiredFieldColorMap.get(bgColor))
							.equals(color)) {
						// mark it for removal from the required field color map
						toBeRemovedFromRequiredMap.add(bgColor);
					}
				}
				// Remove references in the required field map now that
				// we are done iterating.
				for (int j = 0; j < toBeRemovedFromRequiredMap.size(); j++) {
					requiredFieldColorMap.remove(toBeRemovedFromRequiredMap
							.get(j));
				}
			}
		}
		// Remove references in the display map now that we are
		// done iterating
		for (int i = 0; i < toBeRemoved.size(); i++) {
			Color color = (Color) toBeRemoved.get(i);
			// Removing from the display map must be done before disposing the
			// color or else the comparison between this color and the one
			// in the map will fail.
			displays.remove(color);
			// Dispose it
			if (DEBUG) {
				System.out.println("Disposing color " + color.toString()); //$NON-NLS-1$
			}
			color.dispose();
		}
		if (DEBUG) {
			System.out.println("Display map is " + displays.toString()); //$NON-NLS-1$
			System.out.println("Color map is " + requiredFieldColorMap.toString()); //$NON-NLS-1$
		}
	}

}