Add stripe patterns algorithm (#89)

* add stripe patterns

* add comments

* add isoline extraction

* fix warnings

* clean up isolines code

* fix isolines extraction

* detect multiple stripes on individual triangles

* extract multiple isolines per triangle

* fix

* proper isoline connection strategy

include/geometrycentral/surface/stripe_patterns.h

@@ -0,0 +1,36 @@
+#pragma once
+
+#include "geometrycentral/surface/embedded_geometry_interface.h"
+#include "geometrycentral/surface/intrinsic_geometry_interface.h"
+#include <vector>
+
+namespace geometrycentral {
+namespace surface {
+
+// Implementation of "Stripe Patterns on Surfaces" [Knoppel et al. 2015]
+// Based on Keenan Crane's original implementation available here:
+// https://www.cs.cmu.edu/~kmcrane/Projects/StripePatterns/code.zip
+
+// Takes as input a geometry along with vertex-based frequencies and a line field (2-RoSy) and outputs a 2\pi-periodic
+// function defined on triangle corners such that the 0 (mod 2\pi)
+// Isolines of this function are stripes perpendicular to the direction field spaced according to the target frequencies
+std::tuple<CornerData<double>, FaceData<int>, FaceData<int>>
+computeStripePattern(IntrinsicGeometryInterface& geometry, const VertexData<double>& frequencies,
+                     const VertexData<Vector2>& directionField);
+
+// Extracts the zero (mod 2pi) level set of the function values defined on the corners
+// Returns a list of vertices and edges suitable for rendering (e.g. with Polyscope)
+// (requires access to explicit vertex positions)
+std::tuple<std::vector<Vector3>, std::vector<std::array<size_t, 2>>>
+extractPolylinesFromStripePattern(EmbeddedGeometryInterface& geometry, const CornerData<double>& values,
+                                  const FaceData<int>& stripeIndices, const FaceData<int>& fieldIndices,
+                                  const VertexData<Vector2>& directionField, bool connectOnSingularities);
+
+// Runs both of the above functions (per-corner data computation and polyline extraction)
+// can optionally connect isolines separated by a singularity using a directionField alignment heuristic
+std::tuple<std::vector<Vector3>, std::vector<std::array<size_t, 2>>>
+computeStripePatternPolylines(EmbeddedGeometryInterface& geometry, const VertexData<double>& frequencies,
+                              const VertexData<Vector2>& directionField, bool connectIsolinesOnSingularities = true);
+
+} // namespace surface
+} // namespace geometrycentral

src/CMakeLists.txt

@@ -51,6 +51,7 @@ SET(SRCS
   surface/intrinsic_mollification.cpp
   surface/tufted_laplacian.cpp
   surface/flip_geodesics.cpp
+  surface/stripe_patterns.cpp
   surface/transfer_functions.cpp
   surface/quadric_error_simplification.cpp
   surface/subdivide.cpp
@@ -130,6 +131,7 @@ SET(HEADERS
   ${INCLUDE_ROOT}/surface/signpost_intrinsic_triangulation.ipp
   ${INCLUDE_ROOT}/surface/simple_idt.h
   ${INCLUDE_ROOT}/surface/simple_polygon_mesh.h
+  ${INCLUDE_ROOT}/surface/stripe_patterns.h
   ${INCLUDE_ROOT}/surface/subdivide.h
   ${INCLUDE_ROOT}/surface/surface_centers.h
   ${INCLUDE_ROOT}/surface/surface_mesh.h