operation -- a gsk:path-operation value
points -- an array of graphene:point-t instances
n-points -- an integer for the points of the operation
weight -- a single float for the weight for conic curves, or unused if not a conic curve

Prototype of the callback function to iterate through the operations of a path. For each operation, the callback function is given operation itself, the points that the operation is applied to in points, and a weight for conic curves. The n-points argument is somewhat redundant, since the number of points can be inferred from the operation.

Each contour of the path starts with a :move operation. Closed contours end with a :close operation.

Since 4.14