I wanted to draw some text in RenderWindow that would be positioned near a sprite, like a label or tag always moving along with the sprite, attached to some point of it and not rotating or scaling regardless of sprite's transformations. And I was really surprised to not find a complementary function to ConvertCoords, that would convert world coordinates to screen coordinates. I believe this to be a frequently occuring task and i guess it is only reasonable to add such functionality to RenderTarget
The ConvertCoords(x, y, view = NULL) function takes x and y global coordinates and transforms them into view coordinates given the current view attached to the render window.
I think the functionality you wanted was to get the sprite's coordinates in terms of where it will be drawn on the screen. It wouldn't make much sense to have a function for sprite saying Sprite::ConvertCoords(view), meaning, you pass in a view and get it's coordinates out in terms of the view. (You could call it, GetPositionInView or something.
What you really want to do is
Window.ConvertCoords(Sprite.GetX(), Sprite.GetY());
as the window will have the view already attached to it.