draw_gouraud_triangle

... is deprecated as in most backends this is a redundant call. Use draw_gouraud_triangles instead. A draw_gouraud_triangle call in a custom Artist can readily be replaced as:

self.draw_gouraud_triangles(gc, points.reshape((1, 3, 2)),
                            colors.reshape((1, 3, 4)), trans)

A draw_gouraud_triangles method can be implemented from an existing draw_gouraud_triangle method as:

transform = transform.frozen()
for tri, col in zip(triangles_array, colors_array):
    self.draw_gouraud_triangle(gc, tri, col, transform)