Android 利用Camera实现中轴3D卡牌翻转效果

在Android系统API中，有两个Camera类：

• android.graphics.Camera
• android.hardware.Camera

第二个应用于手机硬件的中相机相关的操作，本文讲述的是利用第一个Camera类实现中轴3D转换的卡牌翻转效果，如图：

3d立体旋转效果.gif

开始之前，先看一下Android系统中的坐标系：

坐标系.png

对应于三维坐标系中的三个方向，Camera提供了三种旋转方法：

• rotateX()
• rotateY()
• rotateX()

调用这三种方法，传入旋转角度参数，即可实现视图沿着坐标轴旋转的功能。本文的中轴3D旋转效果就是让视图沿着Y轴旋转的。

系统API Demos中已经为我们提供了一个非常好用的3D旋转动画的工具类：
Rotate3dAnimation.java：

package com.feng.androidtest;

import android.graphics.Camera;
import android.graphics.Matrix;
import android.util.Log;
import android.view.animation.Animation;
import android.view.animation.Transformation;

/**
 * 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();

        Log.i("interpolatedTime", interpolatedTime+"");
        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);
    }
}

可以看出， Rotate3dAnimation 总共做了两件事：在构造函数中赋值了旋转动画所需要的参数，以及重写（override）父类Animation中的applyTransformation()方法，下面分类阐述一下：

• fromDegrees与toDegrees
  视图旋转的开始角度和结束角度，当toDegree处于90倍数时，视图将变得不可见。

• centerX与centerY
  视图旋转的中心点。

• depthZ
  Z轴移动基数，用于计算Camera在Z轴移动距离

• reverse
  boolean类型，控制Z轴移动方向，达到视觉远近移动导致的视图放大缩小效果。

• applyTransformation()
  根据动画播放的时间 interpolatedTime （动画start到end的过程，interpolatedTime从0.0变化到1.0），让Camera在Z轴方向上进行相应距离的移动，实现视觉上远近移动的效果。然后调用 rotateX()方法，让视图围绕Y轴进行旋转，产生3D立体旋转效果。最后再通过Matrix来确定旋转的中心点的位置。

activity_main.xml布局文件：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:background="@android:color/white" >

    <Button
        android:id="@+id/btn_open"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_margin="16dp"
        android:onClick="onClickView"
        android:text="打开"
        android:textColor="@android:color/black"
        android:textSize="16sp" />

    <RelativeLayout
        android:id="@+id/rl_content"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_below="@id/btn_open"
        android:layout_marginTop="16dp" 
        android:background="@android:color/black">

        <ImageView
            android:id="@+id/iv_logo"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:contentDescription="@null"
            android:src="@drawable/ic_qrcode" 
            android:scaleType="centerInside"/>

        <TextView
            android:id="@+id/tv_desc"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:padding="16dp"
            android:text="技术鸟\n\n微信号：NiaoTech\n\n上谈【安卓】,下论【苹果】.以扯淡的态度,面对操蛋的技术,用幽默的语言,诠释开发的经典。"
            android:textColor="@android:color/white"
            android:textSize="18sp" 
            android:visibility="gone"/>
    </RelativeLayout>

</RelativeLayout>

布局中配置了卡牌正面的图片控件，卡牌背面的文本控件，以及他们的parent容器，也就是本文中的旋转动画的执行对象。

MainActivity.java文件：

package com.feng.androidtest;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.animation.AccelerateInterpolator;
import android.view.animation.Animation;
import android.view.animation.Animation.AnimationListener;
import android.view.animation.DecelerateInterpolator;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.RelativeLayout;
import android.widget.TextView;

import com.example.androidtest.R;

/**
 * 
 * @author 亦枫，微信公众号：技术鸟
 * @see http://blog.csdn.net/growing_tree
 */
public class MainActivity extends Activity {
    
    private RelativeLayout mContentRl;
    private ImageView mLogoIv;
    private TextView mDescTv;
    private Button mOpenBtn;
    
    private int centerX;
    private int centerY;
    private int depthZ = 400;
    private int duration = 600;
    private Rotate3dAnimation openAnimation;
    private Rotate3dAnimation closeAnimation;
    
    private boolean isOpen = false;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        mContentRl = (RelativeLayout) findViewById(R.id.rl_content);
        mLogoIv = (ImageView) findViewById(R.id.iv_logo);
        mDescTv = (TextView) findViewById(R.id.tv_desc);
        mOpenBtn = (Button) findViewById(R.id.btn_open);
        
    }
    
    /**
     * 卡牌文本介绍打开效果：注意旋转角度
     */
    private void initOpenAnim() {
        //从0到90度，顺时针旋转视图，此时reverse参数为true，达到90度时动画结束时视图变得不可见，
        openAnimation = new Rotate3dAnimation(0, 90, centerX, centerY, depthZ, true);
        openAnimation.setDuration(duration);
        openAnimation.setFillAfter(true);
        openAnimation.setInterpolator(new AccelerateInterpolator());
        openAnimation.setAnimationListener(new AnimationListener() {
            
            @Override
            public void onAnimationStart(Animation animation) {
                
            }
            
            @Override
            public void onAnimationRepeat(Animation animation) {
                
            }
            
            @Override
            public void onAnimationEnd(Animation animation) {
                mLogoIv.setVisibility(View.GONE);
                mDescTv.setVisibility(View.VISIBLE);
                
                //从270到360度，顺时针旋转视图，此时reverse参数为false，达到360度动画结束时视图变得可见
                Rotate3dAnimation rotateAnimation = new Rotate3dAnimation(270, 360, centerX, centerY, depthZ, false);
                rotateAnimation.setDuration(duration);
                rotateAnimation.setFillAfter(true);
                rotateAnimation.setInterpolator(new DecelerateInterpolator());
                mContentRl.startAnimation(rotateAnimation);
            }
        });
    }
    
    /**
     * 卡牌文本介绍关闭效果：旋转角度与打开时逆行即可
     */
    private void initCloseAnim() {
        closeAnimation = new Rotate3dAnimation(360, 270, centerX, centerY, depthZ, true);
        closeAnimation.setDuration(duration);
        closeAnimation.setFillAfter(true);
        closeAnimation.setInterpolator(new AccelerateInterpolator());
        closeAnimation.setAnimationListener(new AnimationListener() {
            
            @Override
            public void onAnimationStart(Animation animation) {
                
            }
            
            @Override
            public void onAnimationRepeat(Animation animation) {
                
            }
            
            @Override
            public void onAnimationEnd(Animation animation) {
                mLogoIv.setVisibility(View.VISIBLE);
                mDescTv.setVisibility(View.GONE);
                
                Rotate3dAnimation rotateAnimation = new Rotate3dAnimation(90, 0, centerX, centerY, depthZ, false);
                rotateAnimation.setDuration(duration);
                rotateAnimation.setFillAfter(true);
                rotateAnimation.setInterpolator(new DecelerateInterpolator());
                mContentRl.startAnimation(rotateAnimation);
            }
        });
    }
    
    public void onClickView(View v) {
        //以旋转对象的中心点为旋转中心点，这里主要不要再onCreate方法中获取，因为视图初始绘制时，获取的宽高为0
        centerX = mContentRl.getWidth()/2;
        centerY = mContentRl.getHeight()/2;
        if (openAnimation == null) {
            initOpenAnim();
            initCloseAnim();
        }
        
        //用作判断当前点击事件发生时动画是否正在执行
        if (openAnimation.hasStarted() && !openAnimation.hasEnded()) {
            return;
        }
        if (closeAnimation.hasStarted() && !closeAnimation.hasEnded()) {
            return;
        }
        
        //判断动画执行
        if (isOpen) {
            mContentRl.startAnimation(closeAnimation);
            
        }else {
            
            mContentRl.startAnimation(openAnimation);
        }
        
        isOpen = !isOpen;
        mOpenBtn.setText(isOpen ? "关闭" : "打开");
    }
}

代码中已对核心的地方做了注释解释，主要弄清楚 rotate3dAnimation构造参数中的 fromDegrees和toDegrees、depthZ、reverse参数，同时在动画中设置了速度插播器，如动画的前半程使用加速器 AccelerateInterpolator，后半程使用减速器 DecelerateInterpolator
，使动画体验更加人性化。

Demo下载：
http://download.csdn.net/detail/wenbitianxiafeng/9382453

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