Method overlay

src/com/cloudream/ishow/algorithm/FaceDetector.java:859–877

(Bitmap src, Bitmap dst, float left, float top, int alpha)

	}

	public static Bitmap overlay(Bitmap src, Bitmap dst, float left, float top, int alpha)
	{
		alpha = Math.min(Math.max(0, alpha), 255);
		if(!dst.isMutable())
			throw new NullPointerException("cannot write to dst Bitmap");
		
		// operations on Canvas, a preferable way!
		Paint paint = new Paint();
		paint.setAntiAlias(true);
		paint.setAlpha(255 - alpha);
		
		Canvas canvas = new Canvas(dst);
		canvas.drawBitmap(dst, 0, 0, paint);
		
		paint.setAlpha(alpha);
		canvas.drawBitmap(src, left, top, paint);

		return dst;
	}
	
	public static Bitmap overlay(Bitmap src, Bitmap dst, Matrix matrix, int alpha)
	{