android bitmap对角线旋转和画图

Bitmap对角线进行旋转（右上左下）：

public Bitmap convert(Bitmap mBitmap, int width, int height) {
		int w = mBitmap.getWidth();
		int h = mBitmap.getHeight();

		Bitmap newBitmap = Bitmap.createBitmap(width, height, Config.ARGB_8888);
		Canvas mCanvas = new Canvas(newBitmap);
		Matrix matrix = new Matrix();
		matrix.postScale(1, -1);
		matrix.postRotate(-90);
		Bitmap mBitmap2 = Bitmap.createBitmap(mBitmap, 0, 0, w, h, matrix, true);
		mCanvas.drawBitmap(mBitmap2, new Rect(0, 0, mBitmap2.getWidth(), mBitmap2.getHeight()), new Rect(0, 0, width, height), null);
		return newBitmap;
	}

  在Bitmap上画图：

    

public Bitmap drawRect(Bitmap bitmap) {
		Paint paint = new Paint();
		paint.setColor(Color.RED);
		paint.setStyle(Style.STROKE);

		Bitmap newBitmap = Bitmap.createBitmap(bitmap.getWidth(), bitmap.getHeight(), Config.ARGB_8888);
		Canvas mCanvas = new Canvas(newBitmap);
		mCanvas.drawBitmap(bitmap, 0, 0, null);
		mCanvas.drawRect(0, 0, 20, 20, paint);
		mCanvas.save(Canvas.ALL_SAVE_FLAG);
		mCanvas.restore();

		return newBitmap;
	}