Module facepair 

The blend between two faces of one solid, which need not share an edge.

A rolling ball does not care whether the solid has an edge where the two supports would meet. It cares where they would meet (for two planes, their own line of intersection) and rolls in the corner that line defines. So a face-face blend between planes is the edge blend seated on a line the solid does not have: found from the planes, cut back to the stretch both faces actually reach, and handed to the same wedge construction.

A step is the shape that names the case: a tall block beside a low one, the tall one’s wall and the low one’s lid facing each other across a corner that belongs to neither.

Curved faces that meet along edges of the solid are blended along those edges by the edge blend, exact or marched. Curved faces that share no edge are blended where the ball’s section is the same all along the corner (surfaces sharing a direction or an axis) by sweeping the corner between the round and the crease from that section, and otherwise by marching the ball round where the two surfaces cross and building the corner from the marched band, as the edge blend does along an edge. Either corner is cut off or fused on.

Functions

blend_faces

Blend two faces of one solid with a rolling ball of the given radius.