孤岛.jpg

前言

android中3D效果大部分是用android.graphics.Camera来实现的，本篇讲述Camera的一个实例来简单了解其使用

效果展示

3D翻转效果.gif

实现

布局文件activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="com.siti.test_lsn23_3dview.MainActivity">

    <com.siti.test_lsn23_3dview.My3DView
        android:id="@+id/my"
        android:layout_width="100dp"
        android:layout_height="100dp"
        android:layout_margin="30dp"
        />
    <SeekBar
        android:id="@+id/seek"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_margin="20dp"
        />

</LinearLayout>

• 布局文件很简单，上面是实现3D翻转的自定义view，下面是一个SeekBar

MainActivity主要代码：

    private My3DView myView;
    private SeekBar seekBar;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        myView = (My3DView) findViewById(R.id.my);
        seekBar = (SeekBar) findViewById(R.id.seek);

        seekBar.setMax(90);
        seekBar.setKeyProgressIncrement(1);
        seekBar.setOnSeekBarChangeListener(new SeekBar.OnSeekBarChangeListener() {
            @Override
            public void onProgressChanged(SeekBar seekBar, int progress, boolean fromUser) {
                myView.setRotateDegree(progress);
            }

            @Override
            public void onStartTrackingTouch(SeekBar seekBar) {

            }

            @Override
            public void onStopTrackingTouch(SeekBar seekBar) {

            }
        });
    }

• Activity代码也很简单，通过监听SeekBar的值改变，传0～90给自定义myView,调用其方法setRotateDegree()来改变翻转状态

自定义My3DView代码：

public class My3DView extends View {
    Paint mPaint;//画笔

    Bitmap b1;//图1
    Bitmap b2;//图2

    Camera camera;//实现翻转的核心类
    Matrix matrix;//存储变化后的矩阵

    int currentDegree;//当前翻转角度
    float axisY;//旋转轴的Y坐标

    int viewWidth;//控件宽
    int viewHeight;//控件高
    public My3DView(Context context, @Nullable AttributeSet attrs) {
        super(context, attrs);
        init();
    }

    /**
     * 初始化
     */
    private void init() {
        camera = new Camera();
        matrix = new Matrix();
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mPaint.setStyle(Paint.Style.FILL);

        b1 = BitmapFactory.decodeResource(getResources(), R.drawable.img1);
        b2 = BitmapFactory.decodeResource(getResources(), R.drawable.img2);

        axisY = 0;
        currentDegree = 0;
    }

    /**
     * 测量大小，根据控件大小按比例缩放图片，使得图片填充整个控件
     * @param widthMeasureSpec
     * @param heightMeasureSpec
     */
    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        viewWidth = getMeasuredWidth();
        viewHeight = getMeasuredHeight();
        if(viewWidth != 0 && viewHeight != 0) {
            b1 = scaleBitmap(b1);
            b2 = scaleBitmap(b2);
        }
    }

    /**
     * 按比例缩放图片
     * @param origin
     * @return
     */
    private Bitmap scaleBitmap(Bitmap origin) {
        if(origin == null) {
            return null;
        }
        int height = origin.getHeight();
        int width = origin.getWidth();
        float scaleWidth = ((float) viewWidth) / width;
        float scaleHeight = ((float) viewHeight) / height;
        Matrix mt = new Matrix();
        mt.postScale(scaleWidth, scaleHeight);
       Bitmap newBitmap = Bitmap.createBitmap(origin, 0, 0,
                width, height, mt, false);
        return newBitmap;
    }

    /**
     * 绘制，实现翻转效果
     * @param canvas
     */
    @Override
    protected void onDraw(Canvas canvas) {
        //绘制下面那张图片
        camera.save();
        camera.rotateX(-currentDegree);//设置旋转角度
        camera.getMatrix(matrix);//获取到旋转后的矩阵
        camera.restore();
        matrix.preTranslate(-viewWidth / 2, 0);//绕自己的Top旋转
        matrix.postTranslate(viewWidth / 2, axisY);//旋转完后移动图片到轴线下面
        canvas.drawBitmap(b1, matrix, mPaint);

        //绘制上面那张图片
        camera.save();
        camera.rotateX(90-currentDegree);
        camera.getMatrix(matrix);
        camera.restore();
        matrix.preTranslate(-viewWidth / 2, -viewHeight);//绕自己的bottom旋转
        matrix.postTranslate(viewWidth / 2, axisY);//旋转完后移动图片到轴线上面
        canvas.drawBitmap(b2, matrix, mPaint);
    }

    /**
     * 设置当前翻转角度，并重新绘制
     * @param degree
     */
    public void setRotateDegree(int degree) {
        currentDegree = degree;
        axisY = degree / 90f * viewHeight;
        invalidate();
    }
}

• 从调用setRotateDegree(int degree)为入口，axisY = degree / 90f * viewHeight计算两张图片的旋转轴的Y坐标，也就是两张图的相交线的Y坐标。invalidate()重新绘制，调用onDraw()方法
• onDraw()方法中，Camera旋转要注意需要先将矩阵平移至坐标中心点，这也是使用Camera使用需要注意的地方
• 特别需要留意Camera变换的坐标系和绘制坐标系是不一样的，最后附上Camera坐标系

Camera坐标系.png