实现3D旋转效果的方法

Android中有一种旋转效果，是将一个图片进行360度的旋转。

Matrix的作用是对平面上的View进行缩放、平移、旋转，每一种操作都配了setXXX、preXXX、postXXX三个函数。

Camera不是物理摄像头，是android.graphic下的一个类，相当于手机的屏幕，他的坐标系是带有Z坐标的。

可以完成对指定View的X,Y,Z轴的变化，所以可以用来完成3D效果。但是变化之后并不是直接作用于View，而是修改View的Matrix的值，最终View再根据Matrix的值来变换。

Android APIDemos中已经提供了一种例子

/**
 * 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);
    }
}

如果不需要做特别的效果的话，可以直接照搬

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

/**
 * @author Administrator
 *
 */
public class Rotate3DAnimation extends Animation {
    // 开始角度 
    private final float mFromDegrees; 
    // 结束角度 
    private final float mToDegrees; 
    // 中心点 
    private final float mCenterX; 
    private final float mCenterY; 
    private final float mDepthZ; 
    // 是否需要扭曲 ，也就是是否有Z轴方向深度的变化
    private final boolean mReverse; 
    // 摄像头 
    private Camera mCamera; 
    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(); 
    } 
 
    /**
     * 生成Transformation,整个动画的过程中会不停的被调用
     * @param interpolatedTime 会逐渐从0增大到1
     * @param Transformation 变换对象
     */
    @Override 
    protected void applyTransformation(float interpolatedTime, Transformation t) { 
        /**
         * 实际上整个过程就是通过Camera计算出要旋转所要修改的Matrix的值
         * 整个函数结束之后，会根据这个Matrix的值进行变化
         * 也就是说实际最终变换依据的依然是Matrix的值
         */
        final float fromDegrees = mFromDegrees; 
        //生成每次的角度
        float degrees = fromDegrees 
                + ((mToDegrees - fromDegrees) * interpolatedTime); 
        final float centerX = mCenterX; 
        final float centerY = mCenterY; 
        final Camera camera = mCamera; 
        final Matrix matrix = t.getMatrix();//获取动画对象的矩阵 
        camera.save();//保存摄像机的状态
        if (mReverse) { //变化的方向是从小往大变
            camera.translate(0.0f, 0.0f, mDepthZ * interpolatedTime); 
        }
        //旋转到指定的角度
        camera.rotateY(degrees); 
        //取得变换后的矩阵，修改Matrix的值
        camera.getMatrix(matrix); 
        camera.restore();//恢复摄像机的状态 ，每次摄像机变换完后，下次又从摄像机初始位置开始变化
        //将变换的中心点设成中心点
        matrix.preTranslate(-centerX, -centerY); 
        matrix.postTranslate(centerX, centerY); 
    } 
}

Activity中的代码

import org.cxjchen.animation.Rotate3DAnimation;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.animation.*;
import android.widget.ImageView;
import android.widget.TextView;


/**
 * @author Administrator
 *
 */
public class Logo_Activity extends Activity {

    private TextView logo_title = null;

    @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);
        setContentView(R.layout.logo_activity);

        logo_title = (TextView)findViewById(R.id.logo_title);
        logo_title.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                applyRotation(0,360);
            }
        });
    }


    private void applyRotation(float start, float end) { 
        // 计算中心点 
        final float centerX = logo_title.getWidth() / 2.0f; 
        final float centerY = logo_title.getHeight() / 2.0f; 
        final Rotate3DAnimation rotation = new Rotate3DAnimation(start, end, 
                centerX, centerY, 360.0f, false); 
        rotation.setDuration(1000L);
        //设置变换后是否维持变换状态
        rotation.setFillAfter(true); 
        rotation.setInterpolator(new AccelerateInterpolator()); 
        // 设置监听 
        rotation.setAnimationListener(new Animation.AnimationListener() {
            
            @Override
            public void onAnimationStart(Animation animation) {
            }
            
            @Override
            public void onAnimationRepeat(Animation animation) {
                
            }
            
            @Override
            public void onAnimationEnd(Animation animation) {
                
            }
        }); 
        logo_title.startAnimation(rotation); 
    } 

}