Drawing on a Mesh

[nsmela]

Good day,

We'd like to draw on a mesh to generate a contour directly on the mesh to extrude. Could you please he;lp us with the following?

• which terms are used for this process?
• which classes and functions could help?

We could start with selecting the triangles (easy way?), but we'd prefer a way that independant of the triangle shapes and sizes. A way to generate a curve and add or subtract from it would be ideal.

[Grantim]

Hello!

Could you please provide more details about "generation" and "extruding"? We have several function that might be helpful to you:
For example

• computeGeodesicPath finds geodesic path between two points on mesh
  

  MeshLib/source/MRMesh/MRSurfacePath.h

  Lines 40 to 45 in af03ad0

  	/// returns intermediate points of the geodesic path from start to end, where it crosses mesh edges;
  	/// It is the same as calling computeGeodesicPathApprox() then reducePath()
  	MRMESH_API Expected<SurfacePath, PathError> computeGeodesicPath( const Mesh & mesh,
  	const MeshTriPoint & start, const MeshTriPoint & end, GeodesicPathApprox atype = GeodesicPathApprox::FastMarching,
  	int maxGeodesicIters = 100 ); ///< the maximum number of iterations to reduce approximate path length and convert it in geodesic path

• cutMeshByContour/cutMeshByContours project contours point from model 3d space onto mesh connects them and then cut mesh along them, creating new edges that might be used for further processing
  

  MeshLib/source/MRMesh/MRContoursCut.h

  Lines 86 to 96 in af03ad0

  	/// Cuts \p mesh by \p contour by projecting all the points
  	/// \param xf transformation from the CSYS of \p contour to the CSYS of \p mesh
  	/// \note \p mesh is modified, see \ref cutMesh for info
  	/// \return Faces to the left of the polyline
  	[[nodiscard]] MRMESH_API Expected<FaceBitSet> cutMeshByContour( Mesh& mesh, const Contour3f& contour, const AffineXf3f& xf = {} );
  	/// Cuts \p mesh by \p contours by projecting all the points
  	/// \param xf transformation from the CSYS of \p contour to the CSYS of \p mesh
  	/// \note \p mesh is modified, see \ref cutMesh for info
  	/// \return Faces to the left of the polyline
  	[[nodiscard]] MRMESH_API Expected<FaceBitSet> cutMeshByContours( Mesh& mesh, const Contours3f& contours, const AffineXf3f& xf = {} );

• alignContoursToMesh (not released yet) and alignTextToMesh creates aligned mesh based on contours or text with desired extrusion, and this mesh can be engraved or embossed to host mesh later.
  

  MeshLib/source/MRMesh/MRAlignContoursToMesh.h

  Lines 36 to 37 in af03ad0

  	/// Creates planar mesh out of given contour and aligns it to given surface
  	MRMESH_API Expected<Mesh> alignContoursToMesh( const Mesh& mesh, const Contours2f& contours, const ContoursMeshAlignParams& params );

  
  

  MeshLib/source/MRSymbolMesh/MRAlignTextToMesh.h

  Lines 35 to 36 in af03ad0

  	// Creates symbol mesh and aligns it to given surface
  	MRSYMBOLMESH_API Expected<Mesh> alignTextToMesh( const Mesh& mesh, const TextMeshAlignParams& params );

Based on your needs different options might be preferable.

[nsmela]

Here's a quick AI mockup:

The idea is that the user draws a region on the face. This selected region of triangles would make a new mesh and be extruded away from the original mesh, making a new manifold model to 3D print.

[Grantim]

Thanks, I see: in this case you would need something like

MeshLib/source/MRMesh/MRContoursCut.h

Lines 86 to 96 in af03ad0

	/// Cuts \p mesh by \p contour by projecting all the points
	/// \param xf transformation from the CSYS of \p contour to the CSYS of \p mesh
	/// \note \p mesh is modified, see \ref cutMesh for info
	/// \return Faces to the left of the polyline
	[[nodiscard]] MRMESH_API Expected<FaceBitSet> cutMeshByContour( Mesh& mesh, const Contour3f& contour, const AffineXf3f& xf = {} );
	/// Cuts \p mesh by \p contours by projecting all the points
	/// \param xf transformation from the CSYS of \p contour to the CSYS of \p mesh
	/// \note \p mesh is modified, see \ref cutMesh for info
	/// \return Faces to the left of the polyline
	[[nodiscard]] MRMESH_API Expected<FaceBitSet> cutMeshByContours( Mesh& mesh, const Contours3f& contours, const AffineXf3f& xf = {} );

(with initial contour - points on surface representing cut path)

Then you will need to fill inner part of the region:

MeshLib/source/MRMesh/MRFillContourByGraphCut.h

Lines 25 to 31 in a3bd666

	/**
	* \brief Fills region located to the left from given contour, by minimizing the sum of metric over the boundary
	* If the computations are terminated by \p progress, then returns the best approximation found by the moment of termination
	* \ingroup MeshSegmentationGroup
	*/
	MRMESH_API FaceBitSet fillContourLeftByGraphCut( const MeshTopology & topology, const EdgePath & contour,
	const EdgeMetric & metric, const ProgressCallback& progress = {} );

So you will obtain inner selection, and than you could either make a new mesh out of it, or extrude it while staying connected with original mesh:

• Disconnect by

  MeshLib/source/MRMesh/MRMesh.h

  Lines 412 to 413 in af03ad0

  	/// creates new mesh from given triangles of this mesh
  	MRMESH_API Mesh cloneRegion( const FaceBitSet & region, bool flipOrientation = false, const PartMapping & map = {} ) const;

• Extrude like in this example: https://meshlib.io/documentation/ExampleMeshExtrude.html

[nsmela]

Thanks!