code: public void setCombinedMatrix(Matrix4 combined, float x, float y,
  			float viewPortWidth, float viewPortHeight) {
  		
  		System.arraycopy(combined.val, 0, this.combined.val, 0, 16);
  		// updateCameraCorners
  		final float halfViewPortWidth = viewPortWidth * 0.5f;
  		x1 = x - halfViewPortWidth;
  		x2 = x + halfViewPortWidth;
  
  		final float halfViewPortHeight = viewPortHeight * 0.5f;
  		y1 = y - halfViewPortHeight;
  		y2 = y + halfViewPortHeight;
  	}
docs: Sets combined camera matrix.
  
  <p>Matrix must be set to work in box2d coordinates, it will be copied
  and used for culling and rendering. Remember to update it if camera
  changes. This will work with rotated cameras.
  
  @param combined
  matrix that include projection and translation matrices
  @param x
  combined matrix position
  @param y
  combined matrix position
  @param viewPortWidth
  NOTE!! use actual size, remember to multiple with zoom value
  if pulled from OrthoCamera
  @param viewPortHeight
  NOTE!! use actual size, remember to multiple with zoom value
  if pulled from OrthoCamera
  
  @see #setCombinedMatrix(OrthographicCamera)