test & doc for SkUnitCubicInterp

include/utils/SkInterpolator.h

 
 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #ifndef SkInterpolator_DEFINED
@@ skipping 103 matching lines @@
     Result timeToValues(SkMSec time, SkScalar values[] = NULL) const;
 
 private:
     SkScalar* fValues;  // pointer into fStorage
 #ifdef SK_DEBUG
     SkScalar(* fScalarsArray)[10];
 #endif
     typedef SkInterpolatorBase INHERITED;
 };
 
-/** Given all the parameters are [0...1], apply the cubic specified by (0,0)
-    (bx,by) (cx,cy) (1,1) to value, returning the answer, also [0...1].
+/** Interpolate a cubic curve, typically to provide an ease-in ease-out transition.
+    All the parameters are in the range of [0...1].
+    The input value is treated as the x-coordinate of the cubic.
+    The output value is the y-coordinate on the cubic at the x-coordinate.
+
+    @param value        The x-coordinate pinned between [0..1].
+    @param bx,by,cx,cy  The cubic control points where the cubic is specified
+                        as (0,0) (bx,by) (cx,cy) (1,1)
+    @return             the corresponding y-coordinate value, from [0..1].
 */
 SkScalar SkUnitCubicInterp(SkScalar value, SkScalar bx, SkScalar by,
                            SkScalar cx, SkScalar cy);
 
 #endif