Section:
New Results
Rendering, Visualization & Illustration
Computing Smooth Surface Contours with Accurate Topology
Figure
11. Contours stylized with tapered strokes [16] . Our method avoids classical breaks and gaps, producing more coherent animated strokes. Red © Pixar
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We have introduced [16] a method for accurately computing
the visible contours of a smooth 3D surface for stylization. This is a
surprisingly difficult problem, and previous methods are prone to topological
errors, such as gaps in the outline. Our approach is to generate, for each
viewpoint, a new triangle mesh with contours that are topologically-equivalent
and geometrically close to those of the original smooth surface. The contours
of the mesh can then be rendered with exact visibility. The core of the
approach is Contour-Consistency, a way to prove topological equivalence between
the contours of two surfaces. Producing a surface tessellation that satisfies
this property is itself challenging; to this end, we introduce a type of
triangle that ensures consistency at the contour. We then introduce an
iterative mesh generation procedure, based on these ideas. This procedure does
not fully guarantee consistency, but errors are not noticeable in our
experiments. Our algorithm can operate on any smooth input surface
representation; we use Catmull-Clark subdivision surfaces in our
implementation.