Comment #2 on issue 1089 by nicolaih...@gmail.com: Roassal should export PNG https://code.google.com/p/moose-technology/issues/detail?id=1089
Yes, somehow your canvas in TRCanvas is only used for shape creations (computePath). Drawing is done with TRMorphs cairo-surface.
AthensCairoSurface has a writeToPng: method for writing the current surface data as a png file.