geometric.polygonReflectY(polygon[, reflectFactor]) reflects a polygon over its horizontal midline. Pass an optional reflectFactor between 0 and 1, where 1 indicates a full reflection, 0 leaves the polygon unchanged, and 0.5 collapses the polygon on its horizontal midline.

Adjust the reflect factor to see polygonReflectY move the polygon across its horizontal midline.

See also Polygon Reflect X.