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Contrast.cs

//
// Contrast.cs
//
// Authors:
//   David Trowbridge
//   Sebastian Dröge <slomo@circular-chaos.org>
//
// Copyright (C) 2006-2007 David Trowbridge
// Copyright (C) 2008 Sebastian Dröge
//
// Permission is hereby granted, free of charge, to any person obtaining
// a copy of this software and associated documentation files (the
// "Software"), to deal in the Software without restriction, including
// without limitation the rights to use, copy, modify, merge, publish,
// distribute, sublicense, and/or sell copies of the Software, and to
// permit persons to whom the Software is furnished to do so, subject to
// the following conditions:
//
// The above copyright notice and this permission notice shall be
// included in all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
// EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
// MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
// NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
// LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
// OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
// WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
//

using System;
using Cairo;

namespace Hyena.Gui
{
    /* Defined colors.  Keep this list alphabetized if you add new ones,
     * but set the enum value to be at the end of the color_regions table
     * in contrast.c to maintain binary compatibility
     */

    public enum ContrastPaletteColor
    {
        Aqua        =  0,
        Black       =  1,
        Blue        =  2,
        Brown       =  3,
        Cyan        =  4,
        DarkBlue    =  5,
        DarkGreen   =  6,
        DarkGrey    =  7,
        DarkRed     =  8,
        Green       =  9,
        Grey        = 10,
        LightBlue   = 11,
        LightBrown  = 12,
        LightGreen  = 13,
        LightGrey   = 14,
        LightRed    = 15,
        Magenta     = 16,
        Orange      = 17,
        Purple      = 18,
        Red         = 19,
        Violet      = 20,
        White       = 21,
        Yellow      = 22,
        Last        = 23
    };

    public static class Contrast
    {

        /* Data for color palette optimization.
         *
         * These numbers are completely arbitrary decisions, uninformed by the experts
         * at crayola.  These colors are defined as boxes within the CIE L*a*b* color
         * space -- while they're not fully inclusive, they are "safe" in that anywhere
         * within a given region is guaranteed to be the expected color.  The data here
         * are endpoints in each dimension of CIELAB, from which the 8 corners of the
         * region are created to test.
         *
         * Add new entries to the end of this list.
         */
        private static readonly float[,] color_regions = {
            {40.0f,  60.0f, -100.0f, -80.0f,  -10.0f,  20.0f}, /* Aqua */
            { 0.0f,  30.0f,    0.0f,   0.0f,    0.0f,   0.0f}, /* Black */
            {25.0f,  35.0f, -100.0f,   0.0f, -100.0f, -50.0f}, /* Blue */
            {30.0f,  60.0f,   30.0f,  50.0f,   70.0f, 100.0f}, /* Brown */
            {50.0f,  65.0f, -100.0f, -30.0f, -100.0f, -50.0f}, /* Cyan */
            { 0.0f,  20.0f,  -40.0f,  50.0f, -100.0f, -60.0f}, /* Dark Blue */
            {20.0f,  35.0f, -100.0f, -70.0f,   60.0f, 100.0f}, /* Dark Green */
            {20.0f,  40.0f,    0.0f,   0.0f,    0.0f,   0.0f}, /* Dark Grey */
            {10.0f,  40.0f,   90.0f, 100.0f,   70.0f, 100.0f}, /* Dark Red */
            {15.0f,  40.0f, -100.0f, -80.0f,   80.0f, 100.0f}, /* Green */
            {35.0f,  60.0f,    0.0f,   0.0f,    0.0f,   0.0f}, /* Grey */
            {40.0f,  50.0f, -100.0f,   0.0f, -100.0f, -60.0f}, /* Light Blue */
            {60.0f,  75.0f,   30.0f,  50.0f,   80.0f, 100.0f}, /* Light Brown */
            {80.0f,  90.0f, -100.0f, -70.0f,   70.0f, 100.0f}, /* Light Green */
            {50.0f,  80.0f,    0.0f,   0.0f,    0.0f,   0.0f}, /* Light Grey */
            {55.0f,  65.0f,   80.0f,  90.0f,   75.0f, 100.0f}, /* Light Red */
            {40.0f,  55.0f,   90.0f, 100.0f,  -50.0f,   0.0f}, /* Magenta */
            {65.0f,  80.0f,   20.0f,  65.0f,   90.0f, 100.0f}, /* Orange */
            {35.0f,  45.0f,   85.0f, 100.0f,  -90.0f, -80.0f}, /* Purple */
            {40.0f,  50.0f,   80.0f, 100.0f,   75.0f, 100.0f}, /* Red */
            {70.0f,  95.0f,   90.0f, 100.0f, -100.0f,   0.0f}, /* Violet */
            {75.0f, 100.0f,    0.0f,   0.0f,    0.0f,   0.0f}, /* White */
            {90.0f, 100.0f,    5.0f,  15.0f,   92.5f, 105.0f}, /* Yellow */
        };

        /* This performs the non-linear transformation that accounts for the gamma curve
         * in sRGB, but avoids numerical problems.
         */

        private static float srgb_to_xyz_g (float K)
        {
            const float a     = 0.055f;
            const float gamma = 2.4f;


            if (K > 0.04045f)
                return (float) Math.Pow((K + a) / (1 + a), gamma);
            else
                return K / 12.92f;
        }

        private static float xyz_to_lab_f(float t)
        {
            if (t > 0.008856f)
                return (float) Math.Pow(t, 1.0f/3.0f);
            else
                return 7.787f*t + 16.0f/116.0f;
        }

        private static void rgb_to_lab(ushort R, ushort G, ushort B, out float L, out float a, out float b)
        {
            float x, y, z, gr, gg, gb, fy;

            /* This is the reference white point.  Since we're treating "RGB" as
             * sRGB, this is the D65 point.
             */

            const float Xn = 0.93819f;
            const float Yn = 0.98705f;
            const float Zn = 1.07475f;

            gr = srgb_to_xyz_g(R / 65535.0f);
            gg = srgb_to_xyz_g(G / 65535.0f);
            gb = srgb_to_xyz_g(B / 65535.0f);

            x = 0.412424f * gr + 0.357579f * gg + 0.180464f * gb;
            y = 0.212656f * gr + 0.715158f * gg + 0.072186f * gb;
            z = 0.019332f * gr + 0.119193f * gg + 0.950444f * gb;

            fy = xyz_to_lab_f(y / Yn);

            L = 116.0f * fy - 16.0f;
            a = 500.0f * (xyz_to_lab_f(x / Xn) - fy);
            b = 200.0f * (fy - xyz_to_lab_f(z / Zn));
        }

        private static float xyz_to_srgb_C(float K)
        {
            const float a     = 0.055f;
            const float gamma = 2.4f;


            if (K > 0.00304f)
                return (1.0f + a) * ((float) Math.Pow(K, (1.0f / gamma))) - a;
            else
                return K * 12.92f;
        }

        private static void lab_to_rgb(float L, float a, float b, out ushort R, out ushort G, out ushort B)
        {
            float x, y, z, fy, fx, fz, delta, delta2, rs, gs, bs;

            const float Xn = 0.93819f;
            const float Yn = 0.98705f;
            const float Zn = 1.07475f;

            fy = (L + 16.0f) / 116.0f;
            fx = fy + a / 500.0f;
            fz = fy - b / 200.0f;
            delta = 6.0f / 29.0f;
            delta2 = (float) Math.Pow(delta, 2.0f);

            if (fx > delta)
                x = Xn * ((float) Math.Pow(fx, 3.0f));
            else
                x = (fx - 16.0f/116.0f) * 3.0f * delta2 * Xn;

            if (fy > delta)
                y = Yn * ((float) Math.Pow(fy, 3.0f));
            else
                y = (fy - 16.0f/116.0f) * 3.0f * delta2 * Yn;


            if (fz > delta)
                z = Zn * ((float) Math.Pow(fz, 3.0f));
            else
                z = (fz - 16.0f/116.0f) * 3.0f * delta2 * Zn;


            rs =  3.2410f * x - 1.5374f * y - 0.4986f * z;
            gs = -0.9692f * x + 1.8760f * y + 0.0416f * z;
            bs =  0.0556f * x - 0.2040f * y + 1.0570f * z;

            float tmp;
            tmp = (float) Math.Floor(xyz_to_srgb_C(rs) * 65535.0f + 0.5f);
            if (tmp < 0.0f)
                R = 0;
            else if (tmp > 65535.0f)
                R = 65535;
            else
                R = (ushort) tmp;

            tmp = (float) Math.Floor(xyz_to_srgb_C(gs) * 65535.0f + 0.5f);
            if (tmp < 0.0f)
                G = 0;
            else if (tmp > 65535.0f)
                G = 65535;
            else
                G = (ushort) tmp;

            tmp = (float) Math.Floor(xyz_to_srgb_C(bs) * 65535.0f + 0.5f);
            if (tmp < 0.0f)
                B = 0;
            else if (tmp > 65535.0f)
                B = 65535;
            else
                B = (ushort) tmp;
        }

        private static float lab_distance(float La, float aa, float ba, float Lb, float ab, float bb)
        {
            float dL, da, db;

            dL = Math.Abs(Lb - La);
            da = Math.Abs(ab - aa);
            db = Math.Abs(bb - ba);

            return (float) Math.Sqrt(dL*dL + da*da + db*db);
        }

        /* Creates a specific color value for a foreground color, optimizing for
         * maximum readability against the background.
         */

        public static Color RenderForegroundColor(Color background, ContrastPaletteColor color)
        {
            float L, a, b;
            int max_color;
            float max_dist;
            float[,] points = new float[8,3];
            float ld, cd;
            int i;

            rgb_to_lab((ushort)(background.R * 255), (ushort)(background.G * 255),
                (ushort)(background.B * 255), out L, out a, out b);

            points[0,0] = color_regions[(int)color,0];
            points[0,1] = color_regions[(int)color,2];
            points[0,2] = color_regions[(int)color,4];

            points[1,0] = color_regions[(int)color,0];
            points[1,1] = color_regions[(int)color,2];
            points[1,2] = color_regions[(int)color,5];

            points[2,0] = color_regions[(int)color,0];
            points[2,1] = color_regions[(int)color,3];
            points[2,2] = color_regions[(int)color,4];

            points[3,0] = color_regions[(int)color,0];
            points[3,1] = color_regions[(int)color,3];
            points[3,2] = color_regions[(int)color,5];

            points[4,0] = color_regions[(int)color,1];
            points[4,1] = color_regions[(int)color,2];
            points[4,2] = color_regions[(int)color,4];

            points[5,0] = color_regions[(int)color,1];
            points[5,1] = color_regions[(int)color,2];
            points[5,2] = color_regions[(int)color,5];

            points[6,0] = color_regions[(int)color,1];
            points[6,1] = color_regions[(int)color,3];
            points[6,2] = color_regions[(int)color,4];

            points[7,0] = color_regions[(int)color,1];
            points[7,1] = color_regions[(int)color,3];
            points[7,2] = color_regions[(int)color,5];

            max_dist = 0;
            max_color = 0;

            for (i = 0; i < 8; i++) {
                float dist = lab_distance(L, a, b, points[i,0], points[i,1], points[i,2]);

                if (dist > max_dist) {
                    max_dist = dist;
                    max_color = i;
                }
            }

            /* If the luminosity distance is really short, extend the vector further
             * out.  This may push it outside the bounds of the region that a color
             * is specified in, but it keeps things readable when the background and
             * foreground are really close.
             */

            ld = Math.Abs(L - points[max_color,0]);
            cd = (float) Math.Sqrt (Math.Pow (Math.Abs (a - points[max_color,1]), 2.0f) + Math.Pow (Math.Abs (b - points[max_color,2]), 2.0f));

            if ((ld < 10.0f) && (cd < 60.0f)) {
                float dL, da, db;

                dL = points[max_color,0] - L;
                da = points[max_color,1] - a;
                db = points[max_color,2] - b;
                points[max_color,0] = L + (dL * 4.0f);
                points[max_color,1] = a + (da * 1.5f);
                points[max_color,2] = b + (db * 1.5f);
            }

            ushort red, green, blue;

            lab_to_rgb(points[max_color,0], points[max_color,1], points[max_color,2], out red, out green, out blue);

            return new Color (red / 255.0, green / 255.0, blue / 255.0);
        }
    }
}

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