/**
 * Android API实现图像扭曲效果
 * @description：
 * @date 2016-7-22 下午2:19:12
 */
public class BitmapMesh extends GraphicsActivity {
 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(new SampleView(this));
 }
 private static class SampleView extends View {
   //定义常量,指定该图片横向被划分为20格
  private static final int WIDTH = 20;
   //定义常量,指定该图片纵向上被划分为20格
  private static final int HEIGHT = 20;
  //记录该图像上包含441个顶点
  private static final int COUNT = (WIDTH + 1) * (HEIGHT + 1);
  //位图
  private final Bitmap mBitmap;
  //数组,记录Bitmap上的21*21个点的坐标
  private final float[] mVerts = new float[COUNT * 2];
   //记录Bitmap上的21*21个点经过扭曲后的坐标
  private final float[] mOrig = new float[COUNT * 2];
  private final Matrix mMatrix = new Matrix();
  private final Matrix mInverse = new Matrix();
  private static void setXY(float[] array, int index, float x, float y) {
   array[index * 2 + 0] = x;
   array[index * 2 + 1] = y;
  }
  public SampleView(Context context) {
   super(context);
   setFocusable(true);
   //加载图片
   mBitmap = BitmapFactory.decodeResource(getResources(), R.raw.beach);
   //获取图像的宽度和高度
   float w = mBitmap.getWidth();
   float h = mBitmap.getHeight();
   //构建扭曲数据
   int index = 0;
   for (int y = 0; y <= HEIGHT; y++) {
    float fy = h * y / HEIGHT;
    for (int x = 0; x <= WIDTH; x++) {
     float fx = w * x / WIDTH;
      //初始化orig,verts数组
     //初始化,orig,verts两个数组均匀地保存了21 * 21个点的x,y坐标　
     setXY(mVerts, index, fx, fy);
     setXY(mOrig, index, fx, fy);
     index += 1;
    }
   }
   //设置平移效果
   mMatrix.setTranslate(10, 10);
   //实现乱矩阵逆向坐标映射
   mMatrix.invert(mInverse);
  }
  @Override
  protected void onDraw(Canvas canvas) {
   canvas.drawColor(0xFFCCCCCC);
   //对matrix的变换应用到canvas上的所有对象.
   canvas.concat(mMatrix);
   /**
    * bitmap　　　　 　需要扭曲的源位图
    * meshWidth 　　控制在横向上把该源位图划成成多少格
    * meshHeight　 　 控制在纵向上把该源位图划成成多少格
    * verts 　　　　　 长度为(meshWidth + 1) * (meshHeight + 1) * 2的数组，它记录了扭曲后的位图各顶点位置
    * vertOffset 控制verts数组中从第几个数组元素开始才对bitmap进行扭曲
    */
   canvas.drawBitmapMesh(mBitmap, WIDTH, HEIGHT, mVerts, 0, null, 0,
     null);
  }
  //根据触摸事件的位置计算verts数组里各元素的值
  private void warp(float cx, float cy) {
   final float K = 10000;
   float[] src = mOrig;
   float[] dst = mVerts;
   for (int i = 0; i < COUNT * 2; i += 2) {
    float x = src[i + 0];
    float y = src[i + 1];
    float dx = cx - x;
    float dy = cy - y;
    float dd = dx * dx + dy * dy;
     //计算每个坐标点与当前点(cx,cy)之间的距离
    float d = FloatMath.sqrt(dd);
     //扭曲度，距离当前点(cx,cy)越远，扭曲度越小
    float pull = K / (dd + 0.000001f);
    pull /= (d + 0.000001f);
    //对dst数组(保存bitmap　上21 * 21个点经过扭曲后的坐标)赋值
    if (pull >= 1) {
     dst[i + 0] = cx;
     dst[i + 1] = cy;
    } else {
      //控制各顶点向触摸事件发生点偏移
     dst[i + 0] = x + dx * pull;
     dst[i + 1] = y + dy * pull;
    }
   }
  }
  private int mLastWarpX = -9999; // don't match a touch coordinate
  private int mLastWarpY;
  @SuppressLint("ClickableViewAccessibility") @Override
  public boolean onTouchEvent(MotionEvent event) {
   float[] pt = { event.getX(), event.getY() };
   //用当前矩阵改变pts中的值，然后存储在pts中，同上，pts也是存储点的坐标的数组
   mInverse.mapPoints(pt);
   int x = (int) pt[0];
   int y = (int) pt[1];
   if (mLastWarpX != x || mLastWarpY != y) {
    mLastWarpX = x;
    mLastWarpY = y;
    warp(pt[0], pt[1]);
    invalidate();
   }
   return true;
  }
 }
}