A method of rendering a scan line of a graphic object image in a scan line renderer for spans of pixels laying between consecutive x-ordered edges intersecting the scan line includes maintaining a set of depths present in the rendering of the scan line, with the set being maintained in depth order. For each span, the set contains at least those depths that are active in the span, and the set is subject to removal of at least one depth at a subsequent span on the scan line where the corresponding depth is no longer active.