Friday, July 16, 2010

Scale bitmap image, using Matrix

Modify the last exercise "Load bitmap file from SD Card", to implement function to post-scale the bitmap image using Matrix.

Scale bitmap image, using Matrix

In order to create a new bitmap with selected scale: A new Matrix object have to be created, with postScale. Then create a new bitmap from the image in SD Card, using the matrix.

Modify 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"
/>
<Spinner
android:id="@+id/scale"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
/>
<ImageView
android:id="@+id/imageview"
android:layout_gravity="center"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:scaleType="center"
/>
</LinearLayout>


AndroidBitmap.java
package com.exercise.AndroidBitmap;

import android.app.Activity;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Matrix;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.Spinner;

public class AndroidBitmap extends Activity {

private final String imageInSD = "/sdcard/er.PNG";

ImageView myImageView;
Spinner spinnerScale;

private static final String[] strScale
= {"0.2x", "0.5x", "1.0x", "2.0x", "5.0x"};
private static final Float[] floatScale
= {0.2F, 0.5F, 1F, 2F, 5F};
private final int defaultSpinnerScaleSelection = 2;

private ArrayAdapter<String> adapterScale;

private float curScale = 1F;

Bitmap bitmap;
int bmpWidth, bmpHeight;

/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);

myImageView = (ImageView)findViewById(R.id.imageview);

spinnerScale = (Spinner)findViewById(R.id.scale);
adapterScale = new ArrayAdapter<String>(this,
android.R.layout.simple_spinner_item, strScale);
adapterScale.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinnerScale.setAdapter(adapterScale);
spinnerScale.setSelection(defaultSpinnerScaleSelection);
curScale = floatScale[defaultSpinnerScaleSelection];

bitmap = BitmapFactory.decodeFile(imageInSD);
bmpWidth = bitmap.getWidth();
bmpHeight = bitmap.getHeight();

drawMatrix();

spinnerScale.setOnItemSelectedListener(spinnerScaleOnItemSelectedListener);

}

private void drawMatrix(){

Matrix matrix = new Matrix();
matrix.postScale(curScale, curScale);

Bitmap resizedBitmap = Bitmap.createBitmap(bitmap, 0, 0, bmpWidth, bmpHeight, matrix, true);
myImageView.setImageBitmap(resizedBitmap);

}

private Spinner.OnItemSelectedListener spinnerScaleOnItemSelectedListener
= new Spinner.OnItemSelectedListener(){

@Override
public void onItemSelected(AdapterView<?> arg0, View arg1,
int arg2, long arg3) {
// TODO Auto-generated method stub
curScale = floatScale[arg2];
drawMatrix();
}

@Override
public void onNothingSelected(AdapterView<?> arg0) {
// TODO Auto-generated method stub
spinnerScale.setSelection(defaultSpinnerScaleSelection);
curScale = floatScale[defaultSpinnerScaleSelection];
}};
}


Download the files.

next: Rotate bitmap image, using Matrix



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