fill
Computes a bounding box in user coordinates covering the area that would be affected (the "inked" area), by a fill operation given the current path and fill parameters. If the current path is empty, returns an empty rectangle ((0,0), (0,0)). Surface dimensions and clipping are not taken into account. Contrast with cairo_path_extents, which is similar but returns non-zero extents for some paths with no inked area, (such as a simple line segment).
Note that fillExtents must necessarily do more work to compute the precise inked areas in light of the fill rule, so cairo_path_extents may be more desirable for sake of performance if the non-inked path extents are desired.
Return
The result of the operation.