Since 1.18a Pango.Context, from a pangocairo font map
Optionalfunc: ShapeRendererFuncCallback function for rendering attributes of type Pango.AttrType.SHAPE, or null to disable shape rendering.
Optionaldnotify: DestroyNotifyCallback that will be called when the context is freed to release data
Sets callback function for context to use for rendering attributes of type Pango.AttrType.SHAPE.
See PangoCairo.ShapeRendererFunc for details.