Android API Demos中有很多非常Nice的例子,这些例子的代码都写的很出色,如果大家把API Demos中的每个例子研究透了,那么恭喜你已经成为一个真正的Android高手了。这也算是给一些比较迷茫的Android开发者一个指出了一个提升自我能力的方向吧。API Demos中的例子众多,今天我们就来模仿其中一个3D变换的特效,来实现一种别样的图片浏览器。
既然是做中轴旋转的特效,那么肯定就要用到3D变换的功能。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:
那我们就开始动手吧,首先创建一个Android项目,起名叫做RotatePicBrowserDemo,然后我们准备了几张图片,用于稍后在图片浏览器中进行浏览。
而API Demos中已经给我们提供了一个非常好用的3D旋转动画的工具类Rotate3dAnimation,这个工具类就是使用Camera来实现的,我们先将这个这个类复制到项目中来,代码如下所示:
- /**
- * 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);
- }
- }
可以看到,这个类的构造函数中接收一些3D旋转时所需用到的参数,比如旋转开始和结束的角度,旋转的中心点等。然后重点看下applyTransformation()方法,首先根据动画播放的时间来计算出当前旋转的角度,然后让Camera也根据动画播放的时间在Z轴进行一定的偏移,使视图有远离视角的感觉。接着调用Camera的rotateY()方法,让视图围绕Y轴进行旋转,从而产生立体旋转的效果。最后通过Matrix来确定旋转的中心点的位置。
有了这个工具类之后,我们就可以借助它非常简单地实现中轴旋转的特效了。接着创建一个图片的实体类Picture,代码如下所示:
- public class Picture {
- /**
- * 图片名称
- */
- private String name;
- /**
- * 图片对象的资源
- */
- private int resource;
- public Picture(String name, int resource) {
- this.name = name;
- this.resource = resource;
- }
- public String getName() {
- return name;
- }
- public int getResource() {
- return resource;
- }
- }
这个类中只有两个字段,name用于显示图片的名称,resource用于表示图片对应的资源。
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标签: Android 图片浏览器 中轴旋转 |