Improve ColorMatrix docs

bug:18415632

Clean up some text, and add a sample.

Change-Id: I39fdda2004e1932831058701f95f67355786ad9d

1 files changed, 61 insertions, 33 deletions

diff --git a/graphics/java/android/graphics/ColorMatrix.java b/graphics/java/android/graphics/ColorMatrix.java
index 1242eb5..64f0c05 100644
--- a/graphics/java/android/graphics/ColorMatrix.java
+++ b/graphics/java/android/graphics/ColorMatrix.java
@@ -21,23 +21,43 @@ import android.util.FloatMath;
 import java.util.Arrays;
 
 /**
- *  4x5 matrix for transforming the color+alpha components of a Bitmap.
- *  The matrix is stored in a single array, and its treated as follows:
+ * 4x5 matrix for transforming the color and alpha components of a Bitmap.
+ * The matrix can be passed as single array, and is treated as follows:
+ *
  * <pre>
  *  [ a, b, c, d, e,
  *    f, g, h, i, j,
  *    k, l, m, n, o,
- *    p, q, r, s, t ]
- * </pre>
+ *    p, q, r, s, t ]</pre>
+ *
+ * <p>
+ * When applied to a color <code>[R, G, B, A]</code>, the resulting color
+ * is computed as:
+ * </p>
+ *
+ * <pre>
+ *   R&rsquo; = a*R + b*G + c*B + d*A + e;
+ *   G&rsquo; = f*R + g*G + h*B + i*A + j;
+ *   B&rsquo; = k*R + l*G + m*B + n*A + o;
+ *   A&rsquo; = p*R + q*G + r*B + s*A + t;</pre>
+ *
+ * <p>
+ * That resulting color <code>[R&rsquo;, G&rsquo;, B&rsquo;, A&rsquo;]</code>
+ * then has each channel clamped to the <code>0</code> to <code>255</code>
+ * range.
+ * </p>
+ *
+ * <p>
+ * The sample ColorMatrix below inverts incoming colors by scaling each
+ * channel by <code>-1</code>, and then shifting the result up by
+ * <code>255</code> to remain in the standard color space.
+ * </p>
  *
- * When applied to a color <code>[r, g, b, a]</code>, the resulting color
- * is computed as (after clamping):
  * <pre>
- *   R' = a*R + b*G + c*B + d*A + e;
- *   G' = f*R + g*G + h*B + i*A + j;
- *   B' = k*R + l*G + m*B + n*A + o;
- *   A' = p*R + q*G + r*B + s*A + t;
- * </pre>
+ *   [ -1, 0, 0, 0, 255,
+ *     0, -1, 0, 0, 255,
+ *     0, 0, -1, 0, 255,
+ *     0, 0, 0, 1, 0 ]</pre>
  */
 @SuppressWarnings({ "MismatchedReadAndWriteOfArray", "PointlessArithmeticExpression" })
 public class ColorMatrix {
@@ -52,24 +72,24 @@ public class ColorMatrix {
     }
 
     /**
-        * Create a new colormatrix initialized with the specified array of values.
+     * Create a new colormatrix initialized with the specified array of values.
      */
     public ColorMatrix(float[] src) {
         System.arraycopy(src, 0, mArray, 0, 20);
     }
-    
+
     /**
      * Create a new colormatrix initialized with the specified colormatrix.
      */
     public ColorMatrix(ColorMatrix src) {
         System.arraycopy(src.mArray, 0, mArray, 0, 20);
     }
-    
+
     /**
      * Return the array of floats representing this colormatrix.
      */
     public final float[] getArray() { return mArray; }
-    
+
     /**
      * Set this colormatrix to identity:
      * <pre>
@@ -84,7 +104,7 @@ public class ColorMatrix {
         Arrays.fill(a, 0);
         a[0] = a[6] = a[12] = a[18] = 1;
     }
-    
+
     /**
      * Assign the src colormatrix into this matrix, copying all of its values.
      */
@@ -98,7 +118,7 @@ public class ColorMatrix {
     public void set(float[] src) {
         System.arraycopy(src, 0, mArray, 0, 20);
     }
-    
+
     /**
      * Set this colormatrix to scale by the specified values.
      */
@@ -114,12 +134,14 @@ public class ColorMatrix {
         a[12] = bScale;
         a[18] = aScale;
     }
-    
+
     /**
      * Set the rotation on a color axis by the specified values.
+     * <p>
      * <code>axis=0</code> correspond to a rotation around the RED color
      * <code>axis=1</code> correspond to a rotation around the GREEN color
      * <code>axis=2</code> correspond to a rotation around the BLUE color
+     * </p>
      */
     public void setRotate(int axis, float degrees) {
         reset();
@@ -153,8 +175,10 @@ public class ColorMatrix {
     /**
      * Set this colormatrix to the concatenation of the two specified
      * colormatrices, such that the resulting colormatrix has the same effect
-     * as applying matB and then applying matA. It is legal for either matA or
-     * matB to be the same colormatrix as this.
+     * as applying matB and then applying matA.
+     * <p>
+     * It is legal for either matA or matB to be the same colormatrix as this.
+     * </p>
      */
     public void setConcat(ColorMatrix matA, ColorMatrix matB) {
         float[] tmp;
@@ -163,7 +187,7 @@ public class ColorMatrix {
         } else {
             tmp = mArray;
         }
-        
+
         final float[] a = matA.mArray;
         final float[] b = matB.mArray;
         int index = 0;
@@ -176,38 +200,43 @@ public class ColorMatrix {
                            a[j + 2] * b[14] + a[j + 3] * b[19] +
                            a[j + 4];
         }
-        
+
         if (tmp != mArray) {
             System.arraycopy(tmp, 0, mArray, 0, 20);
         }
     }
 
     /**
-     * Concat this colormatrix with the specified prematrix. This is logically
-     * the same as calling setConcat(this, prematrix);
+     * Concat this colormatrix with the specified prematrix.
+     * <p>
+     * This is logically the same as calling setConcat(this, prematrix);
+     * </p>
      */
     public void preConcat(ColorMatrix prematrix) {
         setConcat(this, prematrix);
     }
 
     /**
-     * Concat this colormatrix with the specified postmatrix. This is logically
-     * the same as calling setConcat(postmatrix, this);
+     * Concat this colormatrix with the specified postmatrix.
+     * <p>
+     * This is logically the same as calling setConcat(postmatrix, this);
+     * </p>
      */
     public void postConcat(ColorMatrix postmatrix) {
         setConcat(postmatrix, this);
     }
 
     ///////////////////////////////////////////////////////////////////////////
-    
+
     /**
-     * Set the matrix to affect the saturation of colors. A value of 0 maps the
-     * color to gray-scale. 1 is identity.
+     * Set the matrix to affect the saturation of colors.
+     *
+     * @param sat A value of 0 maps the color to gray-scale. 1 is identity.
      */
     public void setSaturation(float sat) {
         reset();
         float[] m = mArray;
-        
+
         final float invSat = 1 - sat;
         final float R = 0.213f * invSat;
         final float G = 0.715f * invSat;
@@ -217,7 +246,7 @@ public class ColorMatrix {
         m[5] = R;       m[6] = G + sat; m[7] = B;
         m[10] = R;      m[11] = G;      m[12] = B + sat;
     }
-    
+
     /**
      * Set the matrix to convert RGB to YUV
      */
@@ -229,7 +258,7 @@ public class ColorMatrix {
         m[5]  = -0.16874f; m[6]  = -0.33126f; m[7]  = 0.5f;
         m[10] = 0.5f;      m[11] = -0.41869f; m[12] = -0.08131f;
     }
-    
+
     /**
      * Set the matrix to convert from YUV to RGB
      */
@@ -242,4 +271,3 @@ public class ColorMatrix {
         m[10] = 1;  m[11] = 1.772f;     m[12] = 0;
     }
 }
-