The QGeometryRenderer class is missing a property to define an offset into the index buffer.
Suppose you have QGeometry data that is shared by multiple QGeometryRenderers, each drawing a different range of indices. Currently the only way to the define the range is to generate a copy of the QGeometry data for every QGeometryRenderer and alter the byte offset of the index attribute. There should be an additional offset defined by the QGeometryRenderer that is added to the byte offset of the index attribute before rendering.