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在Android中使用矩阵进行图像缩放和拖动

androidimagedrag-and-dropzooming
13

我成功地实现了以下代码（来自Ed Burnette的《Hello Android》），并且能够对图像进行拖动和缩放。

import android.app.Activity;
import android.graphics.Matrix;
import android.graphics.PointF;
import android.os.Bundle;
import android.util.FloatMath;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.widget.ImageView;

public class Touch extends Activity implements OnTouchListener {
   private static final String TAG = "Touch";
   // These matrices will be used to move and zoom image
   Matrix matrix = new Matrix();
   Matrix savedMatrix = new Matrix();

   // We can be in one of these 3 states
   static final int NONE = 0;
   static final int DRAG = 1;
   static final int ZOOM = 2;
   int mode = NONE;

   // Remember some things for zooming
   PointF start = new PointF();
   PointF mid = new PointF();
   float oldDist = 1f;

   @Override
   public void onCreate(Bundle savedInstanceState) {
      super.onCreate(savedInstanceState);
      setContentView(R.layout.main);
      ImageView view = (ImageView) findViewById(R.id.imageView);
      view.setOnTouchListener(this);
   }

   @Override
   public boolean onTouch(View v, MotionEvent event) {
      ImageView view = (ImageView) v;

      // Dump touch event to log
      dumpEvent(event);

      // Handle touch events here...
      switch (event.getAction() & MotionEvent.ACTION_MASK) {
      case MotionEvent.ACTION_DOWN:
         savedMatrix.set(matrix);
         start.set(event.getX(), event.getY());
         Log.d(TAG, "mode=DRAG");
         mode = DRAG;
         break;
      case MotionEvent.ACTION_POINTER_DOWN:
         oldDist = spacing(event);
         Log.d(TAG, "oldDist=" + oldDist);
         if (oldDist > 10f) {
            savedMatrix.set(matrix);
            midPoint(mid, event);
            mode = ZOOM;
            Log.d(TAG, "mode=ZOOM");
         }
         break;
      case MotionEvent.ACTION_UP:
      case MotionEvent.ACTION_POINTER_UP:
         mode = NONE;
         Log.d(TAG, "mode=NONE");
         break;
      case MotionEvent.ACTION_MOVE:
         if (mode == DRAG) {
            // ...
            matrix.set(savedMatrix);
            matrix.postTranslate(event.getX() - start.x,
                  event.getY() - start.y);
         }
         else if (mode == ZOOM) {
            float newDist = spacing(event);
            Log.d(TAG, "newDist=" + newDist);
            if (newDist > 10f) {
               matrix.set(savedMatrix);
               float scale = newDist / oldDist;
               matrix.postScale(scale, scale, mid.x, mid.y);
            }
         }
         break;
      }

      view.setImageMatrix(matrix);
      return true; // indicate event was handled
   }

   /** Show an event in the LogCat view, for debugging */
   private void dumpEvent(MotionEvent event) {
      String names[] = { "DOWN", "UP", "MOVE", "CANCEL", "OUTSIDE",
            "POINTER_DOWN", "POINTER_UP", "7?", "8?", "9?" };
      StringBuilder sb = new StringBuilder();
      int action = event.getAction();
      int actionCode = action & MotionEvent.ACTION_MASK;
      sb.append("event ACTION_").append(names[actionCode]);
      if (actionCode == MotionEvent.ACTION_POINTER_DOWN
            || actionCode == MotionEvent.ACTION_POINTER_UP) {
         sb.append("(pid ").append(
               action >> MotionEvent.ACTION_POINTER_ID_SHIFT);
         sb.append(")");
      }
      sb.append("[");
      for (int i = 0; i < event.getPointerCount(); i++) {
         sb.append("#").append(i);
         sb.append("(pid ").append(event.getPointerId(i));
         sb.append(")=").append((int) event.getX(i));
         sb.append(",").append((int) event.getY(i));
         if (i + 1 < event.getPointerCount())
            sb.append(";");
      }
      sb.append("]");
      Log.d(TAG, sb.toString());
   }

   /** Determine the space between the first two fingers */
   private float spacing(MotionEvent event) {
      float x = event.getX(0) - event.getX(1);
      float y = event.getY(0) - event.getY(1);
      return FloatMath.sqrt(x * x + y * y);
   }

   /** Calculate the mid point of the first two fingers */
   private void midPoint(PointF point, MotionEvent event) {
      float x = event.getX(0) + event.getX(1);
      float y = event.getY(0) + event.getY(1);
      point.set(x / 2, y / 2);
   }
}

然而，能否有人清楚地解释一下上述代码中以下5行的功能呢？

savedMatrix.set(matrix);
matrix.set(savedMatrix);
matrix.postTranslate(event.getX() - start.x,event.getY() - start.y);
float scale = newDist / oldDist;
matrix.postScale(scale, scale, mid.x, mid.y);

感谢提前解释 :)

1
你可能需要添加“imgView.setScaleType（ScaleType.MATRIX）;”才能使用此代码。 - ethrbunny
我在哪里可以找到完整的代码？ - eyal
这段代码似乎工作正常，我的意思是我可以看到关于移动，拖动等的所有Logcat消息，但我的ImageView不会在屏幕上移动或缩放，很奇怪，问题可能是什么？ - Frank Eno
2个回答
8
savedMatrix.set(matrix);

将“matrix”内容复制到“savedMatrix”中

matrix.postTranslate(event.getX() - start.x,event.getY() - start.y);

"矩阵"决定了一些变换，比如缩放和移动。 "postTranslate" 将 "移动" 变换添加到已在 "矩阵" 中定义的变换中。也就是说， "矩阵" 包含某些缩放变换，然后在应用 postTranslate 后，它将确定 "缩放然后移动" 的变换。

float scale = newDist / oldDist;
matrix.postScale(scale, scale, mid.x, mid.y);

将以(mid.x, mid.y)为中心的缩放变换添加到已定义在“matrix”中的变换中。
1
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