JAL-2965 graduated sequence point colour from back to front

[jalview.git] / src / jalview / util / ColorUtils.java

diff --git a/src/jalview/util/ColorUtils.java b/src/jalview/util/ColorUtils.java
index 60129fb..16ff259 100644 (file)
--- a/src/jalview/util/ColorUtils.java
+++ b/src/jalview/util/ColorUtils.java
@@ -31,6 +31,9 @@ import java.util.Random;
 
 public class ColorUtils
 {
+  // constant borrowed from java.awt.Color
+  private static final float FACTOR = 0.7f;
+
   private static final int MAX_CACHE_SIZE = 1729;
   /*
    * a cache for colours generated from text strings
@@ -372,4 +375,63 @@ public class ColorUtils
 
     return col;
   }
+
+  /**
+   * Generates a colour that is interpolated between
+   * <code>colour.darker()</code> and <code>colour.brighter()</code> in
+   * proportion as <code>value</code> is between <code>min</code> and
+   * <code>max</code>. Note that the 'neutral point' (unchanged colour) is
+   * closer to 'brighter' than to 'darker'as this is a geometric range.
+   * 
+   * @param value
+   * @param min
+   * @param max
+   * @param colour
+   * @return
+   */
+  public static Color getGraduatedColour(float value, float min, float max,
+          Color colour)
+  {
+    /*
+     * this computes the equivalent of
+     * getGraduatedColour(value, min, colour.darker(), max, colour.brighter())
+     * but avoiding object creation except for the return value
+     */
+    if (value < min)
+    {
+      value = min;
+    }
+    if (value > max)
+    {
+      value = max;
+    }
+
+    int r = colour.getRed();
+    int g = colour.getGreen();
+    int b = colour.getBlue();
+
+    /*
+     * rgb for colour.darker():
+     */
+    float minR = r * FACTOR;
+    float minG = g * FACTOR;
+    float minB = b * FACTOR;
+
+    /*
+     * rgb for colour.brighter():
+     */
+    float maxR = Math.min(255f, r / FACTOR);
+    float maxG = Math.min(255f, g / FACTOR);
+    float maxB = Math.min(255f, b / FACTOR);
+
+    /*
+     * interpolation
+     */
+    float p = (value - min) / (max - min);
+    int newR = (int) (minR + p * (maxR - minR));
+    int newG = (int) (minG + p * (maxG - minG));
+    int newB = (int) (minB + p * (maxB - minB));
+
+    return new Color(newR, newG, newB, colour.getAlpha());
+  }
 }