浅谈Android实现3D旋转

本文主要记录有关View以及Bitmap的3D旋转效果的实现方法与相关思考。

1 使用Animation实现View的3D旋转

采用继承Animation的方法实现View的3D旋转效果，在ApiDemos里面有详细的代码，具体路径为src/com/example/android/apis/animation/Rotate3dAnimation.java

贴一下代码，记录一下：

/* * Copyright (C) 2007 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.example.android.apis.animation;import android.view.animation.Animation;import android.view.animation.Transformation;import android.graphics.Camera;import android.graphics.Matrix;/** * An animation that rotates the view on the Y axis between two specified angles. * This animation also adds a translation on the Z axis (depth) to improve the effect. */public class Rotate3dAnimation extends Animation {    private final float mFromDegrees;    private final float mToDegrees;    private final float mCenterX;    private final float mCenterY;    private final float mDepthZ;    private final boolean mReverse;    private Camera mCamera;    /**     * Creates a new 3D rotation on the Y axis. The rotation is defined by its     * start angle and its end angle. Both angles are in degrees. The rotation     * is performed around a center point on the 2D space, definied by a pair     * of X and Y coordinates, called centerX and centerY. When the animation     * starts, a translation on the Z axis (depth) is performed. The length     * of the translation can be specified, as well as whether the translation     * should be reversed in time.     *     * @param fromDegrees the start angle of the 3D rotation     * @param toDegrees the end angle of the 3D rotation     * @param centerX the X center of the 3D rotation     * @param centerY the Y center of the 3D rotation     * @param reverse true if the translation should be reversed, false otherwise     */    public Rotate3dAnimation(float fromDegrees, float toDegrees,            float centerX, float centerY, float depthZ, boolean reverse) {        mFromDegrees = fromDegrees;        mToDegrees = toDegrees;        mCenterX = centerX;        mCenterY = centerY;        mDepthZ = depthZ;        mReverse = reverse;    }    @Override    public void initialize(int width, int height, int parentWidth, int parentHeight) {        super.initialize(width, height, parentWidth, parentHeight);        mCamera = new Camera();    }    @Override    protected void applyTransformation(float interpolatedTime, Transformation t) {        final float fromDegrees = mFromDegrees;        float degrees = fromDegrees + ((mToDegrees - fromDegrees) * interpolatedTime);        final float centerX = mCenterX;        final float centerY = mCenterY;        final Camera camera = mCamera;        final Matrix matrix = t.getMatrix();        camera.save();        if (mReverse) {            camera.translate(0.0f, 0.0f, mDepthZ * interpolatedTime);        } else {            camera.translate(0.0f, 0.0f, mDepthZ * (1.0f - interpolatedTime));        }        camera.rotateY(degrees);        camera.getMatrix(matrix);        camera.restore();        matrix.preTranslate(-centerX, -centerY);        matrix.postTranslate(centerX, centerY);    }}

具体我也就不分析了，网上有很多的详细的说明，这里最主要的是applyTransformation函数，该函数第一个参数是当前动画的进度范围在[0, 1]，该函数根据当前的动画进度interpolatedTime，先得出当前帧的y轴旋转角度degrees，然后计算出当前帧的变换矩阵Matrix。

调用上述代码实现旋转：

        final float centerX = mContainer.getWidth() / 2.0f;        final float centerY = mContainer.getHeight() / 2.0f;        final Rotate3dAnimation rotation =                new Rotate3dAnimation(start, end, centerX, centerY, 310.0f, true);        rotation.setDuration(500);        rotation.setFillAfter(true);        rotation.setInterpolator(new AccelerateInterpolator());        rotation.setAnimationListener(new DisplayNextView(position));        mContainer.startAnimation(rotation);

上面的mContainer可以是任意的一个View，如果想再旋转回来，只要调用：

Rotate3dAnimation(-90, 0, centerX, centerY, 310.0f, false);  

2 Camera、Matrix、Canvas实现ImageView的3D旋转

Android中动画的本质还是矩阵变换，每种变换对应着不同的矩阵，上述applyTransformation函数计算了每一帧变换的Matrix，下面就直接用Matrix来变换ImageView，实现3D旋转动画，与Animation方法不同的是：Animation自带了动画的驱动以及每一帧的计算，如果不借助系统提供的Animation框架，则需要自己计算每一帧，同时驱动每一帧动画的更新，下面模拟一下简易的动画过程，模拟每16ms刷新一帧的效果，其实很简单，就是每16ms发送一条消息，驱动下一帧动画的计算和刷新（Animation框架用的是Choreographer，这个对象的postCallback函数可以传进来一个Runnable，同时去请求下一个同步信号，在信号被SurfaceFlinger回调回来的时候运行前面的Runnbale对象，但是这个方法是hide的）。

 public void scheduleAnimation() {if (!mStarted) {    return;}Message msg = mHandler.obtainMessage();mHandler.sendMessageDelayed(msg, 15);}    public class InnerHandler extends Handler {        public void handleMessage(Message msg) {            scheduleAnimation();        }    }

用这种方法只能简单的模拟动画的过程，肯定是不准确的，因为每个消息在MessageQueue中排队，实际被执行的时间是不确定的，这里只是简单的模拟动画的过程，下面需要计算每一帧的变换矩阵Matrix：

    protected Matrix applyTransformation(float interpolatedTime) {          final float fromDegrees = mFromDegrees;          // 生成中间角度          float degrees = fromDegrees                  + ((mToDegrees - fromDegrees) * interpolatedTime);            final float centerX = mCenterX;          final float centerY = mCenterY;          final Camera camera = mCamera;            final Matrix matrix = new Matrix();            camera.save();          if (mReverse) {              camera.translate(0.0f, 0.0f, mDepthZ * interpolatedTime);          } else {              camera.translate(0.0f, 0.0f, mDepthZ * (1.0f - interpolatedTime));          }          camera.rotateY(degrees);          camera.getMatrix(matrix);          camera.restore();            matrix.preTranslate(-centerX, -centerY);          matrix.postTranslate(centerX, centerY);                  return matrix;    }

计算出变换的Matrix以后可以使用，需要利用该Matrix调用ImageView.setImageMatrix方法。使用该方法需要注意将scaleType属性设置为"matrix"

    <ImageView        android:id="@+id/img1"        android:layout_width="200dp"        android:layout_height="200dp"        android:layout_gravity="left"        android:scaleType="matrix"        android:src="@drawable/img1_1" />

3 Camera、Matrix、Canvas实现Bitmap的3D旋转

这种方法是利用第二种方法中的动画驱动框架，手动计算出当前的每一帧Bitmap，然后显示到ImageView上面。

首先做一些必要的Bitmap、Canvas的初始化：

mImg = (ImageView)findViewById(R.id.img1);mCanvas = new Canvas();mSrcBitmap = ((BitmapDrawable)getResources().getDrawable(R.drawable.img1_1)).getBitmap();mBitmap = Bitmap.createBitmap(mSrcBitmap.getWidth(), mSrcBitmap.getHeight(), Config.ARGB_8888);mCanvas.setBitmap(mBitmap);

根据变换矩阵，计算出每一帧Bitmap：

mBitmap.eraseColor(0);Matrix matrix = applyTransformation(progress);mCanvas.drawBitmap(mSrcBitmap, matrix, null);mImg.setImageBitmap(mBitmap);

这样就能够实现图片的3D旋转动画，这里需要主要的一点是，每次在绘制Bitmap之前，都需要将Bitmap清空，否则有些像素在本次绘制的时候没有绘制到，会保留之前的像素值，造成动画异常。

源码下载：https://github.com/houliang/Android-Widget3DRotation