Rotating a drawable in Android

Question

How can a Drawable loaded from a resource be rotated when it is drawn? For example, I would like to draw an arrow and be able to rotate it to face in different directions when it is drawn?

Answer 1

You need to use Bitmap and Canvas Class functions to prepare drawable:

Bitmap bmpOriginal = BitmapFactory.decodeResource(this.getResources(), R.drawable.image2);
Bitmap bmResult = Bitmap.createBitmap(bmpOriginal.getWidth(), bmpOriginal.getHeight(), Bitmap.Config.ARGB_8888);
Canvas tempCanvas = new Canvas(bmResult); 
tempCanvas.rotate(90, bmpOriginal.getWidth()/2, bmpOriginal.getHeight()/2);
tempCanvas.drawBitmap(bmpOriginal, 0, 0, null);

mImageView.setImageBitmap(bmResult);

In this code sample rotation for 90 degrees over image center occurs.

Answer 2

essentially it can be boiled down to: do a(n inverse) canvas transformation instead of transforming drawable

private BitmapDrawable drawable; // or Drawable

protected void onDraw(Canvas canvas) { // inherited from View 
  //...
  canvas.save();
  canvas.rotate(degrees, pivotX, pivotY);
  drawable.draw(canvas);
  canvas.restore();
  //...
}

if you have BitmapDrawable it may be desirable to increase quality of the output by setting antialiasing

drawable.setAntialias(true);