1 files changed, 55 insertions, 0 deletions
diff --git a/src/com/android/launcher3/touch/OverScroll.java b/src/com/android/launcher3/touch/OverScroll.java
new file mode 100644
index 000000000..dc801ec4c
--- /dev/null
+++ b/src/com/android/launcher3/touch/OverScroll.java
@@ -0,0 +1,55 @@
+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package com.android.launcher3.touch;
+
+/**
+ * Utility methods for overscroll damping and related effect.
+ */
+public class OverScroll {
+
+    private static final float OVERSCROLL_DAMP_FACTOR = 0.07f;
+
+    /**
+     * This curve determines how the effect of scrolling over the limits of the page diminishes
+     * as the user pulls further and further from the bounds
+     *
+     * @param f The percentage of how much the user has overscrolled.
+     * @return A transformed percentage based on the influence curve.
+     */
+    private static float overScrollInfluenceCurve(float f) {
+        f -= 1.0f;
+        return f * f * f + 1.0f;
+    }
+
+    /**
+     * @param amount The original amount overscrolled.
+     * @param max The maximum amount that the View can overscroll.
+     * @return The dampened overscroll amount.
+     */
+    public static int dampedScroll(float amount, int max) {
+        if (Float.compare(amount, 0) == 0) return 0;
+
+        float f = amount / max;
+        f = f / (Math.abs(f)) * (overScrollInfluenceCurve(Math.abs(f)));
+
+        // Clamp this factor, f, to -1 < f < 1
+        if (Math.abs(f) >= 1) {
+            f /= Math.abs(f);
+        }
+
+        return Math.round(OVERSCROLL_DAMP_FACTOR * f * max);
+    }
+}