/*******************************************************************************

 * Copyright (c) 2004 IBM Corporation and others.

 * All rights reserved. This program and the accompanying materials 

 * are made available under the terms of the Common Public License v1.0

 * which accompanies this distribution, and is available at

 * http://www.eclipse.org/legal/cpl-v10.html

 * 

 * Contributors:

 *     IBM Corporation - initial API and implementation

 *******************************************************************************/

package org.eclipse.ui.internal.themes;

import java.util.Hashtable;

import org.eclipse.core.runtime.CoreException;

import org.eclipse.core.runtime.IConfigurationElement;

import org.eclipse.core.runtime.IExecutableExtension;

import org.eclipse.swt.graphics.RGB;

import org.eclipse.ui.themes.IColorFactory;

/**

 * A <code>IColorFactory</code> that may be used to select a colour with

 * a higher contrast.  The colors to blend are specified as per method

 * number two in  {@link org.eclipse.core.runtime.IExecutableExtension}.

 * <p>

 * Example usage:

 * <br/>

 * <code>

 * <colorDefinition

 *     label="Red/Blue Contrast"

 *     id="example.redblueblend">

 *     <colorFactory 

 * 				plugin="org.eclipse.ui" 

 * 				class="org.eclipse.ui.internal.themes.RGBContrastFactory">

 *      	<parameter name="foreground" value="0,0,0" />

 *  		<parameter name="background1" value="COLOR_RED" />

 *          <parameter name="background2" value="COLOR_BLUE" />

 *     </colorFactory>

 * </colorDefinition>

 * </code>

 * </p>

 * 

 * <p>

 * This will select whichever of Red or Blue has a higher contrst with black.

 * The color values may be specified as RGB triples or as SWT constants.

 * </p>

 * 

 * @see org.eclipse.swt.SWT

 * @since 3.0

 */

public class RGBContrastFactory implements IColorFactory, IExecutableExtension {

    private String fg, bg1, bg2;

    /**

     * Returns the intensity of an RGB component using the

     * sRGB gamma function.

     * 

     * @param val Value to convert.

     * @return Light intensity of the component.

     */

    double voltage_to_intensity_srgb( double val ) {   

        /* Handle invalid values before doing a gamma transform. */

        if( val < 0.0 ) return 0.0;

        if( val > 1.0 ) return 1.0;

        if( val <= 0.04045 ) {

            return val / 12.92;

        }

        return Math.pow( ( val + 0.055 ) / 1.055, 2.4 );

    }

    /**

     * Returns a measure of the lightness in the perceptual colourspace

     * IPT.

     * 

     * @param color The colour in sRGB

     * @return Lightness in IPT space.

     */

    double lightness( RGB color ) {

        double r = voltage_to_intensity_srgb( color.red / 255.0 );

        double g = voltage_to_intensity_srgb( color.green / 255.0 );

        double b = voltage_to_intensity_srgb( color.blue / 255.0 );

        double l = (0.3139 * r) + (0.6395 * g) + (0.0466 * b);

        double m = (0.1516 * r) + (0.7482 * g) + (0.1000 * b);

        double s = (0.0177 * r) + (0.1095 * g) + (0.8729 * b);

        double lp, mp, sp;

        if( l < 0.0 ) lp = -Math.pow( -l, 0.43 ); else lp = Math.pow( l, 0.43 );

        if( m < 0.0 ) mp = -Math.pow( -m, 0.43 ); else mp = Math.pow( m, 0.43 );

        if( s < 0.0 ) sp = -Math.pow( -s, 0.43 ); else sp = Math.pow( s, 0.43 );

        return (0.4000 * lp) + (0.4000 *mp) + (0.2000 * sp);

    }

    public RGB createColor() {

        /**

         * Determine which pair has a higher contrast by selecting

         * the colour with the furthest distance in lightness.

         */

        RGB cfg, cbg1, cbg2;

        if( fg != null ) {

            cfg = ColorUtils.getColorValue( fg );

        } else {

            cfg = new RGB(255,255,255);

        }

        if( bg1 != null ) {

            cbg1 = ColorUtils.getColorValue( bg1 );

        } else {

            cbg1 = new RGB(0, 0, 0);

        }

        if( bg2 != null ) {

            cbg2 = ColorUtils.getColorValue( bg2 );

        } else {

            cbg2 = new RGB(0, 0, 0);

        }

        double lfg = lightness( cfg );

        double lbg1 = lightness( cbg1 );

        double lbg2 = lightness( cbg2 );

        if( Math.abs(lbg1 - lfg) > Math.abs(lbg2 - lfg) ) {

            return cbg1;

        } else {

            return cbg2;

        }

    }

    /**

     * This executable extension requires parameters to be explicitly declared 

     * via the second method described in the <code>IExecutableExtension</code> 

     * documentation.  This class expects that there will be three parameters, 

     * <code>foreground</code>, <code>background1</code> and

     * <code>background2</code>, that describe the two colors to be blended.

     * These values may either be RGB triples or SWT constants.

     * 

     * @see org.eclipse.core.runtime.IExecutableExtension#setInitializationData(org.eclipse.core.runtime.IConfigurationElement, java.lang.String, java.lang.Object)

     */

    public void setInitializationData(IConfigurationElement config,

            String propertyName, Object data) throws CoreException {

        if (data instanceof Hashtable) {

            Hashtable table = (Hashtable)data;

            fg = (String) table.get("foreground"); //$NON-NLS-1$

            bg1 = (String) table.get("background1"); //$NON-NLS-1$

            bg2 = (String) table.get("background2"); //$NON-NLS-1$

        }

    }

}