Summary

draw_gouraud_triangle is used as the primitive drawing method of the base draw_gouraud_triangles.

However, a backend that overloads draw_gouraud_triangles may not have to define a draw_gouraud_triangle method (except that it may be a suitable name) as any code only calls draw_gouraud_triangles at the "top level".

This leads to that some draw_gouraud_triangle methods will never be called (e.g. Agg, PDF and PS backends), where the PDF and PS backends actually does it the other way round:

Proposed fix

Is it realistic that there will be an artist that calls draw_gouraud_triangle directly or should we just drop those unused methods and somehow clarify that if draw_gouraud_triangles is overloaded in a backend, there is no need to overload draw_gouraud_triangle? (If there is ever such an artist, we can just use the PDF/PS backend code to use draw_gouraud_triangles instead.) Not sure if there is some documentation about what methods a backend is expected to have though.

It seems to be a waste maintaining code that in practice is dead.