CloseSubpath

CloseSubpath is a graphical operation used to terminate the current subpath by drawing a straight line from the current endpoint to the starting point of that subpath. This converts an open chain of edges into a closed shape, which can affect how the path is filled and stroked in subsequent rendering steps.

The exact behavior and naming vary by graphics APIs. In many vector graphics systems, including PostScript, PDF, and SVG, the concept is implemented as a close operation (for SVG, the path command is typically Z or z). Some programming libraries expose a method such as closeSubpath on a path object (for example, QPainterPath::closeSubpath in Qt). In these contexts, closing a subpath usually connects to the subpath’s initial point and sets the current point to that starting point.

Closing a subpath can influence fill rules and visual results. Once closed, the subpath is treated as a single, enclosed region according to the active fill rule (such as nonzero or even-odd). For strokes, the closing edge is part of the path, which can alter the appearance of the outline. If the subpath is already closed or has zero length, invoking the operation may have no visible effect, though some implementations still reset the current point.

Usage considerations include whether a shape should be filled as a unit, whether subsequent operations should continue a new subpath, and how closing interacts with transformations or path optimization. In some workflows, you close a subpath to prepare a shape for filling or clipping, then start a new subpath for additional drawing.