Generate a mirror image using Matrix.postConcat()

Generate a mirror image using Matrix.postConcat()

We can use the matrix below, with the Matrix.postConcat() to generate a mirror image about Y axis.
{ -1, 0, 0,
0, 1, 0,
0, 0, 1
};



main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
   android:orientation="vertical"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   >
<TextView 
   android:layout_width="fill_parent"
   android:layout_height="wrap_content"
   android:text="@string/hello"
   />
<CheckBox
 android:id="@+id/enablemirror"
 android:layout_width="fill_parent"
 android:layout_height="wrap_content"
 android:text="Mirror Image"
 />
<ImageView 
   android:id="@+id/imageview"
   android:layout_gravity="center"
   android:layout_width="fill_parent"
   android:layout_height="fill_parent"
   android:scaleType="center"
   />
</LinearLayout>

AndroidMirrorImage.java

package com.exercise.AndroidMirrorImage;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Matrix;
import android.os.Bundle;
import android.widget.CheckBox;
import android.widget.CompoundButton;
import android.widget.ImageView;

public class AndroidMirrorImage extends Activity {
 
 private final String imageInSD = "/sdcard/google.png";
 
 CheckBox enableMirror;
 ImageView myImageView;
 
 Bitmap bitmap;
 int bmpWidth, bmpHeight;
 
 Matrix matrixMirrorY;
 
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        enableMirror = (CheckBox)findViewById(R.id.enablemirror);
        myImageView = (ImageView)findViewById(R.id.imageview);
        
        enableMirror.setOnCheckedChangeListener(new CheckBox.OnCheckedChangeListener(){

   @Override
   public void onCheckedChanged(CompoundButton buttonView,
     boolean isChecked) {
    // TODO Auto-generated method stub
    drawMatrix();
   }});
        
        bitmap = BitmapFactory.decodeFile(imageInSD);
        bmpWidth = bitmap.getWidth();
        bmpHeight = bitmap.getHeight();
        
        initMirrorMatrix();
       
        drawMatrix();
    }
    
    private void initMirrorMatrix()
    {
     float[] mirrorY = 
     {  -1, 0, 0, 
      0, 1, 0,  
      0, 0, 1    
     };
     matrixMirrorY = new Matrix();
     matrixMirrorY.setValues(mirrorY);
    }
    
    private void drawMatrix()
    {
     if(enableMirror.isChecked())
     {
      Matrix matrix = new Matrix();
      matrix.postConcat(matrixMirrorY); 

      Bitmap mirrorBitmap = Bitmap.createBitmap(bitmap, 0, 0, bmpWidth, bmpHeight, matrix, true);
      myImageView.setImageBitmap(mirrorBitmap);
     }
     else{
      myImageView.setImageBitmap(bitmap);
     }   
    }
}

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previous: Skew bitmap image, using Matrix

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