code: private float getSource(float dest, float destMin, float srcMin, float ratio) {
  
  		float destDistance = dest - destMin;
  		float srcDistance = destDistance * ratio;
  		float ySource = srcMin + srcDistance;
  
  		return ySource;
  	}
docs: Determine the source pixel location
  
  @param dest
  destination pixel location
  @param destMin
  destination minimum most pixel
  @param srcMin
  source minimum most pixel
  @param ratio
  source over destination length ratio
  @return source pixel