在android中使用矩阵缩放和拖动图像

Posted 2023-05-08

【中文标题】在android中使用矩阵缩放和拖动图像

【英文标题】：zooming and dragging images using matrix in android

【发布时间】：2011-08-18 09:57:56

【问题描述】：

我得到以下代码（来自 Ed Burnette 的 Hello android）运行良好，我可以拖动和缩放图像。

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);
   

但是，有人能解释清楚上面代码中以下5行的功能吗？

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);

提前感谢您的解释:)

【问题讨论】：

您可能需要添加 'imgView.setScaleType(ScaleType.MATRIX);'使用此代码。

在哪里可以找到完整的代码？

这段代码似乎工作正常，我的意思是我可以看到所有关于移动、拖动等的 Logcat 消息，但是我的 ImageView 没有在屏幕上移动，也没有缩放、有线的东西，可能是什么问题是？

【参考方案1】：

savedMatrix.set(matrix);

将“矩阵”内容复制到“保存矩阵”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”转换添加到“矩阵”中已经定义的转换。 IE。 “矩阵”包含一些缩放变换，然后在应用 postTranslate 后会确定“缩放然后移动”变换。

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

将中心在 (mid.x, mid.y) 的缩放变换添加到“矩阵”中已经定义的变换

【参考方案2】：

对于替代解决方案，我使用了 Android 开发博客中的示例。 http://android-developers.blogspot.com/2010/06/making-sense-of-multitouch.html

我使用此示例而不是您实现的示例的主要原因是他们编写了博客文章的修改版本。本文介绍如何在未安装 Android 2.2 或更高版本的设备上处理多点触控事件。 http://android-developers.blogspot.com/2010/07/how-to-have-your-cupcake-and-eat-it-too.html