ConvexHull Manual

Table of Contents

• About
• ConvexHullInterface
• Further Reading

About

The maxon::ConvexHullInterface allows to compute a convex polygon hull that encapsulates a given set of points in 3D space.

ConvexHullInterface

The maxon::ConvexHullInterface class provides only one function that can either accept a maxon::ConvexHullData argument or several arrays:

• maxon::ConvexHullInterface::ComputeConvexHull(): Creates the convex hull from the given set of points.

The maxon::ConvexHullData structure contains these members:

• maxon::ConvexHullData::vertices: Vertices of the convex hull.
• maxon::ConvexHullData::edges: Edges of the convex hull. See maxon::ConvEdge.
• maxon::ConvexHullData::faces: Faces of the convex hull. A face is defined by the index of the first edge.

  // This example creates a convex polygon hull around the given array of points.
  // The created polygon data is copied to a PolygonObject.
  // compute convex hull from the given array of points
  maxon::ConvexHullData hullData;
  const maxon::Float    res = maxon::ConvexHullInterface::ComputeConvexHull(points, 0.0, 0.0, hullData) iferr_return;
  if (res < 0)
    return maxon::OK;
 
  // create the PolygonObject
 
  const Int32 polyCount = (Int32)hullData.faces.GetCount();
  const Int32 vertexCount = (Int32)hullData.vertices.GetCount();
 
  PolygonObject* const polyObject = PolygonObject::Alloc(vertexCount, polyCount);
  if (polyObject == nullptr)
    return maxon::OutOfMemoryError(MAXON_SOURCE_LOCATION);
 
  // set polygons
 
  CPolygon* const polygons = polyObject->GetPolygonW();
  Int32 polyCounter = 0;
 
  const maxon::ConvEdge* lastEdge;
 
  // loop over all faces
  for (Int32 faceIndex = 0; faceIndex < polyCount; faceIndex++)
  {
    const maxon::ConvEdge* currentEdge = &hullData.edges[hullData.faces[faceIndex]];
    lastEdge = currentEdge;
 
    const Int firstPoint = lastEdge->_start;
 
    // loop over all edges
    for (currentEdge = &hullData.edges[lastEdge->_nextEdgeOfFace];
         &hullData.edges[currentEdge->_nextEdgeOfFace] != &hullData.edges[hullData.faces[faceIndex]];
         currentEdge = &hullData.edges[currentEdge->_nextEdgeOfFace])
    {
      polygons[polyCounter] = CPolygon((Int32)firstPoint, (Int32)currentEdge->_start, (Int32)currentEdge->_end);
      polyCounter++;
      lastEdge = currentEdge;
    }
  }
 
  // set point positions
  Vector* const polyPoints = polyObject->GetPointW();
  for (Int32 pointIndex = 0; pointIndex < vertexCount; pointIndex++)
    polyPoints[pointIndex] = hullData.vertices[pointIndex];
 
  // insert polygon object into the scene
  polyObject->Message(MSG_UPDATE);
  doc->InsertObject(polyObject, nullptr, nullptr);

Further Reading

• Modeling
• Vectors
• BaseArray Manual