Pull up all apps interaction

First phase implementation: dragging and animation interaction is implemented
namely in two classes. ScrollGestureDetector and AllAppsTransitionController.

FeatureFlag.LAUNCHER#_ALL_APPS_PULL_UP will be true for only AOSP and
not in the extending builds. This way, we can safely iterate without
turning it on the shipped ready version.
b/28917826

Change-Id: I0501309c0121880ffe0555f82d6ac5a145581bb1

src/com/android/launcher3/allapps/VerticalPullDetector.java

@@ -0,0 +1,196 @@
+package com.android.launcher3.allapps;
+
+import android.content.Context;
+import android.util.Log;
+import android.view.MotionEvent;
+import android.view.ViewConfiguration;
+
+/**
+ * One dimensional scroll gesture detector for all apps container pull up interaction.
+ */
+public class VerticalPullDetector {
+
+    private static final String TAG = "ScrollGesture";
+    private static final boolean DBG = false;
+
+    private float mTouchSlop;
+
+    private boolean mAllAppsVisible;
+    private boolean mAllAppsScrollAtTop;
+
+    /**
+     * The minimum release velocity in pixels per millisecond that triggers fling..
+     */
+    private static final float RELEASE_VELOCITY_PX_MS = 1.7f;
+
+    /**
+     * The time constant used to calculate dampening in the low-pass filter of scroll velocity.
+     * Cutoff frequency is set at 10 Hz.
+     */
+    public static final float SCROLL_VELOCITY_DAMPENING_RC = 1000f / (2f * (float) Math.PI * 10);
+
+    /* Scroll state, this is set to true during dragging and animation. */
+    boolean mScrolling;
+
+
+    float mDownY;
+    float mDownMillis;
+
+    float mLastY;
+    float mLastMillis;
+
+    float mVelocity;
+    float mLastDisplacement;
+    float mDisplacement;
+
+    /* scroll started during previous animation */
+    boolean mSubtractSlop = true;
+
+    /* Client of this gesture detector can register a callback. */
+    Listener mListener;
+
+    public void setListener(Listener l) {
+        mListener = l;
+    }
+
+    interface Listener{
+        /**
+         * @param start when should
+         */
+        void onScrollStart(boolean start);
+        boolean onScroll(float displacement, float velocity);
+        void onScrollEnd(float velocity, boolean fling);
+    }
+
+    public VerticalPullDetector(Context context) {
+        mTouchSlop = ViewConfiguration.get(context).getScaledTouchSlop();
+    }
+
+    public void setAllAppsState(boolean allAppsVisible, boolean scrollAtTop) {
+        mAllAppsVisible = allAppsVisible;
+        mAllAppsScrollAtTop = scrollAtTop;
+    }
+
+    private boolean shouldScrollStart() {
+        if (mAllAppsVisible && mDisplacement > mTouchSlop && mAllAppsScrollAtTop) {
+            return true;
+        }
+        if (!mAllAppsVisible && mDisplacement < -mTouchSlop) {
+            return true;
+        }
+        return false;
+    }
+
+    public boolean onTouchEvent(MotionEvent ev) {
+        switch (ev.getAction()) {
+            case MotionEvent.ACTION_DOWN:
+                mDownMillis = ev.getDownTime();
+                mDownY = ev.getY();
+                mLastDisplacement = 0;
+                mVelocity = 0;
+
+                if (mScrolling) {
+                    reportScrollStart(true /* recatch */);
+                }
+                break;
+            case MotionEvent.ACTION_MOVE:
+                mDisplacement = computeDisplacement(ev);
+                mVelocity = computeVelocity(ev, mVelocity);
+
+                if (!mScrolling && shouldScrollStart()) {
+                    mScrolling = true;
+                    reportScrollStart(false /* recatch */);
+                }
+                if (mScrolling && mListener != null) {
+                    reportScroll();
+                }
+                break;
+            case MotionEvent.ACTION_CANCEL:
+            case MotionEvent.ACTION_UP:
+                // These are synthetic events and there is no need to update internal values.
+                if (mScrolling && mListener != null) {
+                    reportScrollEnd();
+                }
+                break;
+            default:
+                //TODO: add multi finger tracking by tracking active pointer.
+                break;
+        }
+        // Do house keeping.
+        mLastDisplacement = mDisplacement;
+
+        mLastY = ev.getY();
+        mLastMillis = ev.getEventTime();
+
+        return true;
+    }
+
+    public void finishedScrolling() {
+        mScrolling = false;
+    }
+
+    private boolean reportScrollStart(boolean recatch) {
+        mListener.onScrollStart(!recatch);
+        if (DBG) {
+            Log.d(TAG, "onScrollStart recatch:" + recatch);
+        }
+        return true;
+    }
+
+    private boolean reportScroll() {
+        float delta = mDisplacement - mLastDisplacement;
+        if (delta != 0) {
+            if (DBG) {
+                Log.d(TAG, String.format("onScroll disp=%.1f, velocity=%.1f",
+                        mDisplacement, mVelocity));
+            }
+            return mListener.onScroll(mDisplacement - (mSubtractSlop? mTouchSlop : 0), mVelocity);
+        }
+        return true;
+    }
+
+    private void reportScrollEnd() {
+        if (DBG) {
+            Log.d(TAG, String.format("onScrolEnd disp=%.1f, velocity=%.1f",
+                    mDisplacement, mVelocity));
+        }
+        mListener.onScrollEnd(mVelocity, Math.abs(mVelocity) > RELEASE_VELOCITY_PX_MS);
+    }
+    /**
+     * Computes the damped velocity using the two motion events and the previous velocity.
+     */
+    private float computeVelocity(MotionEvent to, float previousVelocity) {
+        float delta = computeDelta(to);
+
+        float deltaTimeMillis = to.getEventTime() - mLastMillis;
+        float velocity = (deltaTimeMillis > 0) ? (delta / deltaTimeMillis) : 0;
+        if (Math.abs(previousVelocity) < 0.001f) {
+            return velocity;
+        }
+
+        float alpha = computeDampeningFactor(deltaTimeMillis);
+        return interpolate(previousVelocity, velocity, alpha);
+    }
+
+    private float computeDisplacement(MotionEvent to) {
+        return to.getY() - mDownY;
+    }
+
+    private float computeDelta(MotionEvent to) {
+        return to.getY() - mLastY;
+    }
+
+    /**
+     * Returns a time-dependent dampening factor using delta time.
+     */
+    private static float computeDampeningFactor(float deltaTime) {
+        return deltaTime / (SCROLL_VELOCITY_DAMPENING_RC + deltaTime);
+    }
+
+    /**
+     * Returns the linear interpolation between two values
+     */
+    private static float interpolate(float from, float to, float alpha) {
+        return (1.0f - alpha) * from + alpha * to;
+    }
+}