I derived my RasteredXYRenderer from StandardXYItemRenderer. It
only displays Shapes (removed the other code to leave it "light" and
understandable if the jfreechart team wants to integrate this code into
the original source but leave it as a wokring renderer).
It now lays a grid over the dataArea and places the items on it. if there
is already an item on that location the renderer searches for the next
ffree location on the grid.