Adnroid上的简单图像合成类——PorterDuffXfermode

public class MainActivity extends Activity implements OnClickListener
{
  static final int PICKED_ONE = 0;
  static final int PICKED_TWO = 1;
  boolean onePicked = false;
  boolean twoPicked = false;
  ImageView compositeImageView;
  Button choosePicture1, choosePicture2;
  Bitmap bmp1, bmp2;
  Canvas canvas;
  Paint paint;
  @Override
  protected void onCreate(Bundle savedInstanceState)
  {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    compositeImageView = (ImageView) findViewById(R.id.ChosenImageView);
    choosePicture1 = (Button) findViewById(R.id.ChoosePictureButton1);
    choosePicture2 = (Button) findViewById(R.id.ChoosePictureButton2);
    choosePicture1.setOnClickListener(this);
    choosePicture2.setOnClickListener(this);
  }
  @Override
  public void onClick(View v)
  {
    // TODO Auto-generated method stub
    int which = -1;
    if (v == choosePicture1)
    {
      which = PICKED_ONE;
    } else
    {
      which = PICKED_TWO;
    }
    Intent choosePictureIntent = new Intent(Intent.ACTION_PICK,
        Media.EXTERNAL_CONTENT_URI);
    startActivityForResult(choosePictureIntent, which);
  }
  private Bitmap loadBitmap(Uri imageFileUri)
  {
    Display currentDisplay = getWindowManager().getDefaultDisplay();
    int dw = currentDisplay.getWidth();
    int dh = currentDisplay.getHeight();
    Bitmap returnBmp = Bitmap.createBitmap(dw, dh, Config.ARGB_4444);
    BitmapFactory.Options bmpFactoryOptions = new BitmapFactory.Options();
    bmpFactoryOptions.inJustDecodeBounds = true;
    try
    {
      returnBmp = BitmapFactory.decodeStream(getContentResolver()
          .openInputStream(imageFileUri), null, bmpFactoryOptions);
    } catch (FileNotFoundException e)
    {
      // TODO Auto-generated catch block
      e.printStackTrace();
    }
    int heightRatio = (int) Math.ceil(bmpFactoryOptions.outHeight
        / (float) dh);
    int widthRatio = (int) Math.ceil(bmpFactoryOptions.outWidth
        / (float) dw);
    if (heightRatio > 1 && widthRatio > 1)
    {
      if (heightRatio > widthRatio)
      {
        bmpFactoryOptions.inSampleSize = heightRatio;
      } else
      {
        bmpFactoryOptions.inSampleSize = widthRatio;
      }
    }
    bmpFactoryOptions.inJustDecodeBounds = false;
    try
    {
      returnBmp = BitmapFactory.decodeStream(getContentResolver()
          .openInputStream(imageFileUri), null, bmpFactoryOptions);
    } catch (FileNotFoundException e)
    {
      // TODO Auto-generated catch block
      e.printStackTrace();
    }
    return returnBmp;
  }
  @Override
  protected void onActivityResult(int requestCode, int resultCode, Intent data)
  {
    // TODO Auto-generated method stub
    super.onActivityResult(requestCode, resultCode, data);
    if (resultCode == RESULT_OK)
    {
      Uri imageFileUri = data.getData();
      if (requestCode == PICKED_ONE)
      {
        bmp1 = loadBitmap(imageFileUri);
        onePicked = true;
      } else
      {
        bmp2 = loadBitmap(imageFileUri);
        twoPicked = true;
      }
      if (onePicked && twoPicked)
      {
        Bitmap drawingBitmap = Bitmap.createBitmap(bmp1.getWidth(),
            bmp1.getHeight(), bmp1.getConfig());
        canvas = new Canvas(drawingBitmap);
        paint = new Paint();
        canvas.drawBitmap(bmp1, 0, 0, paint);
        paint.setXfermode(new PorterDuffXfermode(
            android.graphics.PorterDuff.Mode.DARKEN));
        canvas.drawBitmap(bmp2, 0, 0, paint);
        compositeImageView.setImageBitmap(drawingBitmap);
      }
    }
  }
}