1 files changed, 20 insertions, 30 deletions

diff --git a/core/java/android/widget/EdgeEffect.java b/core/java/android/widget/EdgeEffect.java
index 3c411126627f..5f55887d6019 100644
--- a/core/java/android/widget/EdgeEffect.java
+++ b/core/java/android/widget/EdgeEffect.java
@@ -130,7 +130,11 @@ public class EdgeEffect {
     public @interface EdgeEffectType {
     }
 
-    private static final float DEFAULT_MAX_STRETCH_INTENSITY = 0.08f;
+    private static final float LINEAR_STRETCH_INTENSITY = 0.03f;
+
+    private static final float EXP_STRETCH_INTENSITY = 0.02f;
+
+    private static final float SCROLL_DIST_AFFECTED_BY_EXP_STRETCH = 0.4f;
 
     @SuppressWarnings("UnusedDeclaration")
     private static final String TAG = "EdgeEffect";
@@ -176,9 +180,6 @@ public class EdgeEffect {
 
     private long mStartTime;
     private float mDuration;
-    private float mStretchIntensity = DEFAULT_MAX_STRETCH_INTENSITY;
-    private float mStretchDistanceFraction = 1f;
-    private float mStretchDistance = -1f;
 
     private final Interpolator mInterpolator = new DecelerateInterpolator();
 
@@ -269,16 +270,6 @@ public class EdgeEffect {
     }
 
     /**
-     * Configure the distance in pixels to stretch the content. This is only consumed as part
-     * if {@link #setType(int)} is set to {@link #TYPE_STRETCH}
-     * @param stretchDistance Stretch distance in pixels when the target View is overscrolled
-     * @hide
-     */
-    public void setStretchDistance(float stretchDistance) {
-        mStretchDistance = stretchDistance;
-    }
-
-    /**
      * Reports if this EdgeEffect's animation is finished. If this method returns false
      * after a call to {@link #draw(Canvas)} the host widget should schedule another
      * drawing pass to continue the animation.
@@ -520,13 +511,6 @@ public class EdgeEffect {
     }
 
     /**
-     * @hide
-     */
-    public void setMaxStretchIntensity(float stretchIntensity) {
-        mStretchIntensity = stretchIntensity;
-    }
-
-    /**
      * Set or clear the blend mode. A blend mode defines how source pixels
      * (generated by a drawing command) are composited with the destination pixels
      * (content of the render target).
@@ -642,22 +626,19 @@ public class EdgeEffect {
             // assume rotations of increments of 90 degrees
             float x = mTmpPoints[10] - mTmpPoints[8];
             float width = right - left;
-            float vecX = Math.max(-1f, Math.min(1f, x / width));
+            float vecX = dampStretchVector(Math.max(-1f, Math.min(1f, x / width)));
             float y = mTmpPoints[11] - mTmpPoints[9];
             float height = bottom - top;
-            float vecY = Math.max(-1f, Math.min(1f, y / height));
+            float vecY = dampStretchVector(Math.max(-1f, Math.min(1f, y / height)));
             renderNode.stretch(
                     left,
                     top,
                     right,
                     bottom,
-                    vecX * mStretchIntensity,
-                    vecY * mStretchIntensity,
-                    // TODO (njawad/mount) figure out proper stretch distance from UX
-                    //  for now leverage placeholder logic if no stretch distance is provided to
-                    //  consume the displacement ratio times the minimum of the width or height
-                    mStretchDistance > 0 ? mStretchDistance :
-                            (mStretchDistanceFraction * Math.max(mWidth, mHeight))
+                    vecX,
+                    vecY,
+                    mWidth,
+                    mHeight
             );
         }
 
@@ -794,4 +775,13 @@ public class EdgeEffect {
         return Math.abs(mVelocity) < VELOCITY_THRESHOLD
                 && Math.abs(displacement) < VALUE_THRESHOLD;
     }
+
+    private float dampStretchVector(float normalizedVec) {
+        float sign = normalizedVec > 0 ? 1f : -1f;
+        float overscroll = Math.abs(normalizedVec);
+        float linearIntensity = LINEAR_STRETCH_INTENSITY * overscroll;
+        double scalar = Math.E / SCROLL_DIST_AFFECTED_BY_EXP_STRETCH;
+        double expIntensity = EXP_STRETCH_INTENSITY * (1 - Math.exp(-overscroll * scalar));
+        return sign * (float) (linearIntensity + expIntensity);
+    }
 }