src/com/android/launcher3/FirstFrameAnimatorHelper.java

/*
 * Copyright (C) 2013 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;

import static com.android.launcher3.util.DefaultDisplay.getSingleFrameMs;

import android.animation.ValueAnimator;
import android.animation.ValueAnimator.AnimatorUpdateListener;
import android.util.Log;
import android.view.View;
import android.view.View.OnAttachStateChangeListener;
import android.view.ViewTreeObserver.OnDrawListener;

/*
 *  This is a helper class that listens to updates from the corresponding animation.
 *  For the first two frames, it adjusts the current play time of the animation to
 *  prevent jank at the beginning of the animation
 */
public class FirstFrameAnimatorHelper implements OnDrawListener, OnAttachStateChangeListener {

    private static final String TAG = "FirstFrameAnimatorHlpr";
    private static final boolean DEBUG = false;
    private static final int MAX_DELAY = 1000;

    private View mRootView;
    private long mGlobalFrameCount;

    public FirstFrameAnimatorHelper(View target) {
        target.addOnAttachStateChangeListener(this);
        if (target.isAttachedToWindow()) {
            onViewAttachedToWindow(target);
        }
    }

    public <T extends ValueAnimator> T addTo(T anim) {
        anim.addUpdateListener(new MyListener());
        return anim;
    }

    @Override
    public void onDraw() {
        mGlobalFrameCount ++;
    }

    @Override
    public void onViewAttachedToWindow(View view) {
        mRootView = view.getRootView();
        mRootView.getViewTreeObserver().addOnDrawListener(this);
    }

    @Override
    public void onViewDetachedFromWindow(View view) {
        if (mRootView != null) {
            mRootView.getViewTreeObserver().removeOnDrawListener(this);
            mRootView = null;
        }
    }

    private class MyListener implements AnimatorUpdateListener {

        private long mStartFrame;
        private long mStartTime = -1;
        private boolean mHandlingOnAnimationUpdate;
        private boolean mAdjustedSecondFrameTime;

        @Override
        public void onAnimationUpdate(final ValueAnimator animation) {
            final long currentTime = System.currentTimeMillis();
            if (mStartTime == -1) {
                mStartFrame = mGlobalFrameCount;
                mStartTime = currentTime;
            }

            final long currentPlayTime = animation.getCurrentPlayTime();
            boolean isFinalFrame = Float.compare(1f, animation.getAnimatedFraction()) == 0;

            if (!mHandlingOnAnimationUpdate &&
                    mRootView != null &&
                    mRootView.getWindowVisibility() == View.VISIBLE &&
                    // If the current play time exceeds the duration, or the animated fraction is 1,
                    // the animation will get finished, even if we call setCurrentPlayTime --
                    // therefore don't adjust the animation in that case
                    currentPlayTime < animation.getDuration() && !isFinalFrame) {
                mHandlingOnAnimationUpdate = true;
                long frameNum = mGlobalFrameCount - mStartFrame;

                // If we haven't drawn our first frame, reset the time to t = 0
                // (give up after MAX_DELAY ms of waiting though - might happen, for example, if we
                // are no longer in the foreground and no frames are being rendered ever)
                if (frameNum == 0 && currentTime < mStartTime + MAX_DELAY && currentPlayTime > 0) {
                    // The first frame on animations doesn't always trigger an invalidate...
                    // force an invalidate here to make sure the animation continues to advance
                    mRootView.invalidate();
                    animation.setCurrentPlayTime(0);
                    // For the second frame, if the first frame took more than 16ms,
                    // adjust the start time and pretend it took only 16ms anyway. This
                    // prevents a large jump in the animation due to an expensive first frame
                } else {
                    int singleFrameMS = getSingleFrameMs(mRootView.getContext());
                    if (frameNum == 1 && currentTime < mStartTime + MAX_DELAY &&
                            !mAdjustedSecondFrameTime &&
                            currentTime > mStartTime + singleFrameMS &&
                            currentPlayTime > singleFrameMS) {
                        animation.setCurrentPlayTime(singleFrameMS);
                        mAdjustedSecondFrameTime = true;
                    } else {
                        if (frameNum > 1) {
                            mRootView.post(() -> animation.removeUpdateListener(this));
                        }
                        if (DEBUG) print(animation);
                    }
                }
                mHandlingOnAnimationUpdate = false;
            } else {
                if (DEBUG) print(animation);
            }
        }

        public void print(ValueAnimator animation) {
            float flatFraction = animation.getCurrentPlayTime() / (float) animation.getDuration();
            Log.d(TAG, mGlobalFrameCount +
                    "(" + (mGlobalFrameCount - mStartFrame) + ") " + mRootView + " dirty? " +
                    mRootView.isDirty() + " " + flatFraction + " " + this + " " + animation);
        }
    }
}