/**
 * Android API實現圖像扭曲效果
 * @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 {
   //定義常量,指定該圖片橫向被劃分為20格
  private static final int WIDTH = 20;
   //定義常量,指定該圖片縱向上被劃分為20格
  private static final int HEIGHT = 20;
  //記錄該圖像上包含441個頂點
  private static final int COUNT = (WIDTH + 1) * (HEIGHT + 1);
  //位圖
  private final Bitmap mBitmap;
  //數組,記錄Bitmap上的21*21個點的坐標
  private final float[] mVerts = new float[COUNT * 2];
   //記錄Bitmap上的21*21個點經過扭曲后的坐標
  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);
   //加載圖片
   mBitmap = BitmapFactory.decodeResource(getResources(), R.raw.beach);
   //獲取圖像的寬度和高度
   float w = mBitmap.getWidth();
   float h = mBitmap.getHeight();
   //構建扭曲數據
   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數組
     //初始化,orig,verts兩個數組均勻地保存了21 * 21個點的x,y坐標　
     setXY(mVerts, index, fx, fy);
     setXY(mOrig, index, fx, fy);
     index += 1;
    }
   }
   //設置平移效果
   mMatrix.setTranslate(10, 10);
   //實現亂矩陣逆向坐標映射
   mMatrix.invert(mInverse);
  }
  @Override
  protected void onDraw(Canvas canvas) {
   canvas.drawColor(0xFFCCCCCC);
   //對matrix的變換應用到canvas上的所有對象.
   canvas.concat(mMatrix);
   /**
    * bitmap　　　　 　需要扭曲的源位圖
    * meshWidth 　　控制在橫向上把該源位圖劃成成多少格
    * meshHeight　 　 控制在縱向上把該源位圖劃成成多少格
    * verts 　　　　　 長度為(meshWidth + 1) * (meshHeight + 1) * 2的數組，它記錄了扭曲后的位圖各頂點位置
    * vertOffset 控制verts數組中從第幾個數組元素開始才對bitmap進行扭曲
    */
   canvas.drawBitmapMesh(mBitmap, WIDTH, HEIGHT, mVerts, 0, null, 0,
     null);
  }
  //根據觸摸事件的位置計算verts數組里各元素的值
  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;
     //計算每個坐標點與當前點(cx,cy)之間的距離
    float d = FloatMath.sqrt(dd);
     //扭曲度，距離當前點(cx,cy)越遠，扭曲度越小
    float pull = K / (dd + 0.000001f);
    pull /= (d + 0.000001f);
    //對dst數組(保存bitmap　上21 * 21個點經過扭曲后的坐標)賦值
    if (pull >= 1) {
     dst[i + 0] = cx;
     dst[i + 1] = cy;
    } else {
      //控制各頂點向觸摸事件發生點偏移
     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() };
   //用當前矩陣改變pts中的值，然后存儲在pts中，同上，pts也是存儲點的坐標的數組
   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;
  }
 }
}