prolooks/GlossGradient.vala

   1 using Gtk;
   2 using Gdk;
   3
   4 // code courtesy http://cocoawithlove.com/2008/09/drawing-gloss-gradients-in-coregraphics.html
   5 // adapted to Vala by Hans Baier
   6
   7 namespace Prolooks {
   8
   9     private static double perceptualGlossFractionForColor(Cairo.Color color) {
  10         double REFLECTION_SCALE_NUMBER = 0.2;
  11         double NTSC_RED_FRACTION       = 0.299;
  12         double NTSC_GREEN_FRACTION     = 0.587;
  13         double NTSC_BLUE_FRACTION      = 0.114;
  14
  15         double glossScale =
  16             NTSC_RED_FRACTION   * color.red   +
  17             NTSC_GREEN_FRACTION * color.green +
  18             NTSC_BLUE_FRACTION  * color.blue;
  19
  20         glossScale = Math.pow(glossScale, REFLECTION_SCALE_NUMBER);
  21
  22         return glossScale;
  23     }
  24
  25     private static Cairo.Color perceptualCausticColorForColor(Cairo.Color input) {
  26         double CAUSTIC_FRACTION             = 0.60;
  27         double COSINE_ANGLE_SCALE           = 1.4;
  28         double MIN_RED_THRESHOLD            = 0.95;
  29         double MAX_BLUE_THRESHOLD           = 0.7;
  30         double GRAYSCALE_CAUSTIC_SATURATION = 0.2;
  31
  32         Cairo.Color source = input;
  33
  34         HSV source_hsv = new HSV();
  35         source_hsv.from_cairo_color(source);
  36
  37         double hue        = source_hsv.hue;
  38         double saturation = source_hsv.saturation;
  39         double value      = source_hsv.value;
  40         double alpha      = input.alpha;
  41
  42         HSV target_hsv = new HSV();
  43         target_hsv.from_cairo_color(new Cairo.Color(1.0, 1.0, 0.0));
  44
  45         double targetHue        = target_hsv.hue;
  46         double targetSaturation = target_hsv.saturation;
  47         double targetValue      = target_hsv.value;
  48
  49         if (saturation < 0.0001) {
  50             hue = targetHue;
  51             saturation = GRAYSCALE_CAUSTIC_SATURATION;
  52         }
  53
  54         if (hue > MIN_RED_THRESHOLD) {
  55             hue -= 1.0;
  56         } else if (hue > MAX_BLUE_THRESHOLD) {
  57             target_hsv.from_cairo_color(new Cairo.Color(1.0, 0.0, 1.0));
  58
  59             targetHue        = target_hsv.hue;
  60             targetSaturation = target_hsv.saturation;
  61             targetValue      = target_hsv.value;
  62         }
  63
  64         double scaledCaustic = CAUSTIC_FRACTION * 0.5 * (1.0 + Math.cos(COSINE_ANGLE_SCALE * Math.PI * (hue - targetHue) / 360.0));
  65
  66         target_hsv.hue        = hue * (1.0 - scaledCaustic) + targetHue * scaledCaustic;
  67         target_hsv.saturation = saturation;
  68         target_hsv.value      = value * (1.0 - scaledCaustic) + targetValue * scaledCaustic;
  69
  70         Cairo.Color target_color = target_hsv.to_cairo_color();
  71         target_color.alpha = alpha;
  72
  73         return target_color;
  74     }
  75
  76     private struct GlossParameters {
  77       Cairo.Color color;
  78       Cairo.Color caustic;
  79       double expCoefficient;
  80       double expScale;
  81       double expOffset;
  82       double initialWhite;
  83       double finalWhite;
  84     }
  85
  86     private static Cairo.Color glossInterpolation(double progress, ref GlossParameters params) {
  87       Cairo.Color output = new Cairo.Color();
  88
  89       if (progress < 0.5)
  90         {
  91           progress = progress * 2.0;
  92
  93           progress =
  94                   1.0 - params.expScale * (Math.exp(progress * (-params.expCoefficient)) - params.expOffset);
  95
  96           double currentWhite = progress * (params.finalWhite - params.initialWhite) + params.initialWhite;
  97
  98           output.red   = params.color.red   * (1.0 - currentWhite) + currentWhite;
  99           output.green = params.color.green * (1.0 - currentWhite) + currentWhite;
 100           output.blue  = params.color.blue  * (1.0 - currentWhite) + currentWhite;
 101           output.alpha = params.color.alpha * (1.0 - currentWhite) + currentWhite;
 102         }
 103       else
 104         {
 105           progress = (progress - 0.5) * 2.0;
 106
 107
 108           progress = params.expScale *
 109                   (Math.exp((1.0 - progress) * (-params.expCoefficient)) - params.expOffset);
 110
 111           output.red   = params.color.red   * (1.0 - progress) + params.caustic.red   * progress;
 112           output.green = params.color.green * (1.0 - progress) + params.caustic.green * progress;
 113           output.blue  = params.color.blue  * (1.0 - progress) + params.caustic.blue  * progress;
 114           output.alpha = params.color.alpha * (1.0 - progress) + params.caustic.alpha * progress;
 115         }
 116
 117           return output;
 118     }
 119
 120     public static Cairo.Pattern gloss_gradient_pattern(double x0, double y0, double x1, double y1, Cairo.Color color, int no_steps = 100) {
 121         double EXP_COEFFICIENT = 1.2;
 122         double REFLECTION_MAX  = 0.60;
 123         double REFLECTION_MIN  = 0.20;
 124
 125         GlossParameters params = GlossParameters();
 126
 127         params.expCoefficient = EXP_COEFFICIENT;
 128         params.expOffset      = Math.exp(-params.expCoefficient);
 129         params.expScale       = 1.0 / (1.0 - params.expOffset);
 130
 131         params.color = color;
 132
 133         params.caustic      = perceptualCausticColorForColor(params.color);
 134
 135         double glossScale   = perceptualGlossFractionForColor(params.color);
 136
 137         params.initialWhite = glossScale * REFLECTION_MAX;
 138         params.finalWhite   = glossScale * REFLECTION_MIN;
 139
 140         Cairo.Pattern result = new Cairo.Pattern.linear(x0, y0, x1, y1);
 141
 142         for (double offset = 0; offset <= 1.0; offset += 1.0 / (double) no_steps) {
 143             Cairo.Color stop = glossInterpolation(offset, ref params);
 144             result.add_color_stop_rgba(offset, stop.red, stop.green, stop.blue, stop.alpha);
 145         }
 146
 147         return result;
 148     }
 149
 150 } // namespace Prolooks