## Effective Removal of Detail for a Multiresolution Viewer: Slide 10 of 12.

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With surfaces, we can only remove a vertex with a zero count if its
parent triangle doesn't have any nonzero children. We don't really
even remove vertices, instead, we collapse triangles into larger
triangles.

In this example, within the large triangle we have two vertices with
nonzero reference counts. We first reduce the reference count of the
vertex on the right. We notice that all its siblings also have zero
counts, and none of them has children, so we collapse the four
triangles into their parent.

When the reference count of the remaining vertex goes to zero, we
begin a cascade of triangle collapses. Now all the triangles and
vertices within the big triangle are removed in a bottom-up order.