android - How to rotate a Bitmap on Canvas center

activity_main.xml 
 <?xml version="1.0" encoding="utf-8"?> <RelativeLayout     xmlns:android="http://schemas.android.com/apk/res/android"     xmlns:tools="http://schemas.android.com/tools"     android:id="@+id/rl"     android:layout_width="match_parent"     android:layout_height="match_parent"     android:padding="16dp"     tools:context=".MainActivity"     android:background="#9ebf98"     >     <ImageView         android:id="@+id/iv"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         />     <Button         android:id="@+id/btn"         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="Draw"         android:layout_alignParentRight="true"         android:layout_alignParentEnd="true"         android:layout_alignParentBottom="true"         /> </RelativeLayout>
MainActivity.java 
 package com.cfsuman.me.androidcode;  import android.content.Context; import android.content.res.Resources; import android.graphics.BitmapFactory; import android.graphics.Color; import android.graphics.Paint; import android.support.v7.app.AppCompatActivity; import android.os.Bundle; import android.view.View; import android.widget.Button; import android.widget.ImageView; import android.widget.RelativeLayout; import android.graphics.Canvas; import android.graphics.Bitmap; import android.graphics.Matrix;   public class MainActivity extends AppCompatActivity {     private Context mContext;     private Resources mResources;     private RelativeLayout mRelativeLayout;     private Button mButton;     private ImageView mImageView;      @Override     protected void onCreate(Bundle savedInstanceState) {         super.onCreate(savedInstanceState);         setContentView(R.layout.activity_main);          // Get the application context         mContext = getApplicationContext();          // Get the Resources         mResources = getResources();          // Get the widgets reference from XML layout         mRelativeLayout = (RelativeLayout) findViewById(R.id.rl);         mButton = (Button) findViewById(R.id.btn);         mImageView = (ImageView) findViewById(R.id.iv);          // Set a click listener for Button widget         mButton.setOnClickListener(new View.OnClickListener() {             @Override             public void onClick(View view) {                 // Get the source bitmap to draw on canvas                 Bitmap srcBitmap = BitmapFactory.decodeResource(                         mResources,                         R.drawable.avatar_girl_small                 );                  // Initialize a new Bitmap                 Bitmap bitmap = Bitmap.createBitmap(                         700, // Width                         500, // Height                         Bitmap.Config.ARGB_8888 // Config                 );                  // Initialize a new Canvas instance                 Canvas canvas = new Canvas(bitmap);                  // Draw a solid color on the canvas as background                 canvas.drawColor(Color.YELLOW);                  // Initialize a new Paint instance to draw on canvas                 Paint paint = new Paint();                 paint.setAntiAlias(true);                 paint.setDither(true);                 paint.setFilterBitmap(true);                  /*                     Matrix                         The Matrix class holds a 3x3 matrix for transforming coordinates.                 */                 /*                      Matrix()                         Create an identity matrix                 */                  // Initialize a new Matrix instance                 Matrix matrix = new Matrix();                  /*                     public void setRotate (float degrees, float px, float py)                         Set the matrix to rotate by the specified number of degrees, with a pivot                         point at (px, py). The pivot point is the coordinate that should remain                         unchanged by the specified transformation.                 */                  // Set rotation on matrix                 matrix.setRotate(                         45, // degrees                         srcBitmap.getWidth() / 2, // px                         srcBitmap.getHeight() / 2 // py                 );                  /*                       postTranslate(float dx, float dy)                             Postconcats the matrix with the specified translation.                 */                  // Draw the bitmap at the center position of the canvas both vertically and horizontally                 matrix.postTranslate(                         canvas.getWidth() / 2 - srcBitmap.getWidth() / 2,                         canvas.getHeight() / 2 - srcBitmap.getHeight() / 2                 );                  /*                     public void drawBitmap (Bitmap bitmap, Matrix matrix, Paint paint)                         Draw the bitmap using the specified matrix.                      Parameters                         bitmap : The bitmap to draw                         matrix : The matrix used to transform the bitmap when it is drawn                         paint : May be null. The paint used to draw the bitmap                 */                  // Finally, draw the bitmap on canvas as a rotated bitmap                 canvas.drawBitmap(                         srcBitmap, // Bitmap                         matrix, // Matrix                         paint // Paint                 );                  // Display the newly created bitmap on app interface                 mImageView.setImageBitmap(bitmap);             }         });     } }
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