Android(安卓)3D旋转动画——Rotate3dAnimation

在Android中如果想要实现3D效果一般有两种选择，一是使用Open GL ES，二是使用Camera。Open GL ES使用起来太过复杂，一般是用于比较高级的3D特效或游戏，像比较简单的一些3D效果，使用Camera就足够了。

Camera中提供了三种旋转方法，分别是rotateX()、rotateY()和rotateZ，调用这三个方法，并传入相应的角度，就可以让视图围绕这三个轴进行旋转，而今天我们要做的中轴旋转效果其实就是让视图围绕Y轴进行旋转。使用Camera让视图进行旋转的示意图，如下所示：

/* * 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.rotatepicbrowserdemo;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();        // 将当前的摄像头位置保存下来，以便变换进行完成后恢复成原位，        camera.save();        // camera.translate，这个方法接受3个参数，分别是x,y,z三个轴的偏移量，我们这里只将z轴进行了偏移，        if (mReverse) {            // z的偏移会越来越大。这就会形成这样一个效果，view从近到远            camera.translate(0.0f, 0.0f, mDepthZ * interpolatedTime);        } else {            // z的偏移会越来越小。这就会形成这样一个效果，我们的View从一个很远的地方向我们移过来，越来越近，最终移到了我们的窗口上面～            camera.translate(0.0f, 0.0f, mDepthZ * (1.0f - interpolatedTime));        }        // 是给我们的View加上旋转效果，在移动的过程中，视图还会移Y轴为中心进行旋转。        camera.rotateY(degrees);        // 是给我们的View加上旋转效果，在移动的过程中，视图还会移X轴为中心进行旋转。        // camera.rotateX(degrees);        // 这个是将我们刚才定义的一系列变换应用到变换矩阵上面，调用完这句之后，我们就可以将camera的位置恢复了，以便下一次再使用。        camera.getMatrix(matrix);        // camera位置恢复        camera.restore();        // 以View的中心点为旋转中心,如果不加这两句，就是以（0,0）点为旋转中心        matrix.preTranslate(-centerX, -centerY);        matrix.postTranslate(centerX, centerY);    }}

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