Blends on Edges

List of:	Discussion Topic
Subjects:	Blending
Contents:	Advanced Blending

	The majority of blends running against edges are moving either forward or backward along the edge, without doubling back on that edge. Such a blend may leave the edge either by reaching one of its vertices or by coming away from the edge onto one of the adjoining faces. In this case, the blend always has an interior face, which is the face on the side that will be "swallowed" when the blend is fixed, and an exterior face, which is the face on the side that will remain.
	Table 1-4. Blends on Edges

Run Into	Transition	How to Obtain
smooth vertex	roll onto next edge	place rollon on edge (default)
smooth vertex	start capping	place cap on next edge
sharp vertex	start capping	place cap on vertex (default)
sharp vertex	roll onto vertex	place rollon on vertex
interior face	roll onto face	no other choice
exterior face	roll onto face	place rollon on face (default)
exterior face	stay on edge	place cap on face

	A smooth vertex is one at which there is another tangent edge incident that can be followed. A sharp vertex is one at which there is no other tangent edge to follow.
	Transitions directly onto a face that occur at one of the ends of the edge are not supported.
	A blend is disallowed from following the edge when it has the option of rolling onto the interior face. Not rolling onto the interior face would violate the rule that concave blends add material and that convex ones remove it.
	Some blends do not move along the edge, but remain wholly stationary at a point on the edge. In such cases the faces cannot be distinguished as either interior or exterior and the blend is forced to roll onto both. The only such blend allowed is the osculating torus produced by blending a plane against a straight line normal to it.

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