Swipe up overshoot always plays

Instead of using an OvershootInterpolator, we adjust the end progress to > 1 and
add a second interpolator to settle back to 1. That way, even if the animation runs
starting very late, e.g. 1.0, it still has room to overshoot. We use this same
OvershootParams class to calculate an overshoot for a blocked long fling as well.

Bug: 109709720
Change-Id: I43152237e4350f93e7c462c22e68d09d05c1dd57

1 files changed, 75 insertions, 7 deletions

diff --git a/src/com/android/launcher3/anim/Interpolators.java b/src/com/android/launcher3/anim/Interpolators.java
index 8a1abf412..1d71c605e 100644
--- a/src/com/android/launcher3/anim/Interpolators.java
+++ b/src/com/android/launcher3/anim/Interpolators.java
@@ -16,7 +16,10 @@
 
 package com.android.launcher3.anim;
 
+import static com.android.launcher3.Utilities.SINGLE_FRAME_MS;
+
 import android.graphics.Path;
+import android.view.animation.AccelerateDecelerateInterpolator;
 import android.view.animation.AccelerateInterpolator;
 import android.view.animation.DecelerateInterpolator;
 import android.view.animation.Interpolator;
@@ -45,6 +48,8 @@ public class Interpolators {
     public static final Interpolator DEACCEL_2_5 = new DecelerateInterpolator(2.5f);
     public static final Interpolator DEACCEL_3 = new DecelerateInterpolator(3f);
 
+    public static final Interpolator ACCEL_DEACCEL = new AccelerateDecelerateInterpolator();
+
     public static final Interpolator FAST_OUT_SLOW_IN = new PathInterpolator(0.4f, 0f, 0.2f, 1f);
 
     public static final Interpolator AGGRESSIVE_EASE = new PathInterpolator(0.2f, 0f, 0f, 1f);
@@ -141,17 +146,12 @@ public class Interpolators {
         return Math.abs(velocity) > FAST_FLING_PX_MS ? SCROLL : SCROLL_CUBIC;
     }
 
-    public static Interpolator overshootInterpolatorForVelocity(float velocity) {
-        return overshootInterpolatorForVelocity(velocity, 1f);
-    }
-
     /**
      * Create an OvershootInterpolator with tension directly related to the velocity (in px/ms).
      * @param velocity The start velocity of the animation we want to overshoot.
-     * @param dampFactor An optional factor to reduce the amount of tension (how far we overshoot).
      */
-    public static Interpolator overshootInterpolatorForVelocity(float velocity, float dampFactor) {
-        return new OvershootInterpolator(Math.min(Math.abs(velocity), 3f) / dampFactor);
+    public static Interpolator overshootInterpolatorForVelocity(float velocity) {
+        return new OvershootInterpolator(Math.min(Math.abs(velocity), 3f));
     }
 
     /**
@@ -183,4 +183,72 @@ public class Interpolators {
             float upperBound) {
         return t -> Utilities.mapRange(interpolator.getInterpolation(t), lowerBound, upperBound);
     }
+
+    /**
+     * Computes parameters necessary for an overshoot effect.
+     */
+    public static class OvershootParams {
+        public Interpolator interpolator;
+        public float start;
+        public float end;
+        public long duration;
+
+        /**
+         * Given the input params, sets OvershootParams variables to be used by the caller.
+         * @param startProgress The progress from 0 to 1 that the overshoot starts from.
+         * @param overshootPastProgress The progress from 0 to 1 where we overshoot past (should
+         *        either be equal to startProgress or endProgress, depending on if we want to
+         *        overshoot immediately or only once we reach the end).
+         * @param endProgress The final progress from 0 to 1 that we will settle to.
+         * @param velocityPxPerMs The initial velocity that causes this overshoot.
+         * @param totalDistancePx The distance against which progress is calculated.
+         */
+        public OvershootParams(float startProgress, float overshootPastProgress,
+                float endProgress, float velocityPxPerMs, int totalDistancePx) {
+            velocityPxPerMs = Math.abs(velocityPxPerMs);
+            start = startProgress;
+            int startPx = (int) (start * totalDistancePx);
+            // Overshoot by about half a frame.
+            float overshootBy = velocityPxPerMs * SINGLE_FRAME_MS / totalDistancePx / 2;
+            overshootBy = Utilities.boundToRange(overshootBy, 0.02f, 0.15f);
+            end = overshootPastProgress + overshootBy;
+            int endPx = (int) (end  * totalDistancePx);
+            int overshootDistance = endPx - startPx;
+            // Calculate deceleration necessary to reach overshoot distance.
+            // Formula: velocityFinal^2 = velocityInitial^2 + 2 * acceleration * distance
+            //          0 = v^2 + 2ad (velocityFinal == 0)
+            //          a = v^2 / -2d
+            float decelerationPxPerMs = velocityPxPerMs * velocityPxPerMs / (2 * overshootDistance);
+            // Calculate time necessary to reach peak of overshoot.
+            // Formula: acceleration = velocity / time
+            //          time = velocity / acceleration
+            duration = (long) (velocityPxPerMs / decelerationPxPerMs);
+
+            // Now that we're at the top of the overshoot, need to settle back to endProgress.
+            float settleDistance = end - endProgress;
+            int settleDistancePx = (int) (settleDistance * totalDistancePx);
+            // Calculate time necessary for the settle.
+            // Formula: distance = velocityInitial * time + 1/2 * acceleration * time^2
+            //          d = 1/2at^2 (velocityInitial = 0, since we just stopped at the top)
+            //          t = sqrt(2d/a)
+            // Above formula assumes constant acceleration. Since we use ACCEL_DEACCEL, we actually
+            // have acceleration to halfway then deceleration the rest. So the formula becomes:
+            //          t = sqrt(d/a) * 2 (half the distance for accel, half for deaccel)
+            long settleDuration = (long) Math.sqrt(settleDistancePx / decelerationPxPerMs) * 2;
+            // How much of the animation to devote to playing the overshoot (the rest is for settle).
+            float overshootFraction = (float) duration / (duration + settleDuration);
+            duration += settleDuration;
+            // Finally, create the interpolator, composed of two interpolators: an overshoot, which
+            // reaches end > 1, and then a settle to endProgress.
+            Interpolator overshoot = Interpolators.clampToProgress(DEACCEL, 0, overshootFraction);
+            // The settle starts at 1, where 1 is the top of the overshoot, and maps to a fraction
+            // such that final progress is endProgress. For example, if we overshot to 1.1 but want
+            // to end at 1, we need to map to 1/1.1.
+            Interpolator settle = Interpolators.clampToProgress(Interpolators.mapToProgress(
+                    ACCEL_DEACCEL, 1, (endProgress - start) / (end - start)), overshootFraction, 1);
+            interpolator = t -> t <= overshootFraction
+                    ? overshoot.getInterpolation(t)
+                    : settle.getInterpolation(t);
+        }
+    }
 }
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