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  3. TSweepingMeshSDF

TSweepingMeshSDF

Compute discretely-sampled (ie gridded) signed distance field for a mesh The basic approach is, first compute exact Distances in a narrow band, and then extend out to rest of Grid using fast "sweeping" (ie like a distance transform).

API > API/Runtime > API/Runtime/GeometryCore > API/Runtime/GeometryCore/Implicit

References

   
Module GeometryCore
Header /Engine/Source/Runtime/GeometryCore/Public/Implicit/SweepingMeshSDF.h
Include #include "Implicit/SweepingMeshSDF.h"

Syntax

template<class TriangleMeshType>  
class TSweepingMeshSDF

Remarks

Compute discretely-sampled (ie gridded) signed distance field for a mesh The basic approach is, first compute exact Distances in a narrow band, and then extend out to rest of Grid using fast "sweeping" (ie like a distance transform). The resulting unsigned Grid is then signed using ray-intersection counting, which is also computed on the Grid, so no BVH is necessary

If you set ComputeMode to NarrowBandOnly, result is a narrow-band signed distance field. This is quite a bit faster as the sweeping is the most computationally-intensive step.

You can optionally provide a spatial data structure to allow faster computation of narrow-band Distances; this is most beneficial if we want a wider band

Caveats:

  • the "narrow band" is based on triangle bounding boxes, so it is not necessarily that "narrow" if you have large triangles on a diagonal to Grid axes

TODO: a number of utility function could & should be shared between this and CachingMeshSDF!

This code is based on the implementation found at https://github.com/christopherbatty/SDFGen

Variables

  Type Name Description
Public variable int ApproxMaxCellsPerDimension If the number of cells in any dimension may exceed this, CellSize will be automatically increased to keep cell count reasonable.
Public variable bool bComputeSigns Should we try to compute signs? if not, Grid remains unsigned
Public variable bool bUseParallel Most of this parallelizes very well, makes a huge speed difference.
Public variable bool bWantClosestTriGrid Implementation computes the triangle closest to each Grid cell, can return this Grid if desired (only reason not to is avoid hanging onto memory)
Public variable bool bWantIntersectionsGrid Grid of per-cell crossing or parity counts.
Public variable TFunction< bool()> CancelF If this function returns true, we should abort calculation
Public variable float CellSize  
Protected variable FDenseGrid3i ClosestTriGrid Grid of closest triangle indices; only available if bWantClosestTriGrid is set to true. Access via GetClosestTriGrid()
Public variable EComputeModes ComputeMode  
Public variable int ExactBandWidth Width of the band around triangles for which exact Distances are computed (In fact this is conservative, the band is often larger locally)
Public variable FVector3d ExpandBounds Bounds of Grid will be expanded this much in positive and negative directions.
Public variable FDenseGrid3f Grid  
Public variable FVector3f GridOrigin  
Public variable EInsideModes InsideMode  
Protected variable FDenseGrid3i IntersectionsGrid Grid of intersection counts; only available if bWantIntersectionsGrid is set to true. Access via GetIntersectionsGrid()
Public variable const TriangleMeshType * Mesh  
Public variable double NarrowBandMaxDistance How wide of narrow band should we compute.
Public variable TMeshAABBTree3< TriangleMeshType > * Spatial  

Constructors

  Type Name Description
Public function  

TSweepingMeshSDF ( const TriangleMeshType* Mesh,
float CellSize,
TMeshAABBTree3< TriangleMeshType >* Spatial
)

  

Functions

  Type Name Description
Public function Const float

At ( int I,
int J,
int K
)

  
Public function Const FVector3f

CellCenter ( int I,
int J,
int K
)

  
Public function bool Compute the SDF
Public function Const FVector3i  
Public function void

Empty ()

 Empty out all computed result data (leaves input data alone)
Public function Const const FDenseGrid3i &  
Public function Const const FDenseGrid3i &  
Public function Const float  
Public function TTriLinearGridInterpolant< TSweepingMeshSDF >  
Public function Static int

Orientation ( double X1,
double Y1,
double X2,
double Y2,
double& TwiceSignedArea
)

 Calculate twice signed area of triangle (0,0)-(X1,Y1)-(X2,Y2) return an SOS-determined sign (-1, +1, or 0 only if it's a truly degenerate triangle)
Public function Static bool

PointInTriangle2d ( double X0,
double Y0,
double X1,
double Y1,
double X2,
double Y2,
double X3,
double Y3,
double& A,
double& B,
double& C
)

 Robust test of (X0,Y0) in the triangle (X1,Y1)-(X2,Y2)-(X3,Y3) if true is returned, the barycentric coordinates are set in A,B,C.
Public function Static float

PointSegmentDistance ( const FVector3f& x0,
const FVector3f& x1,
const FVector3f& x2
)

 Find distance x0 is from segment x1-x2
Public function Static double

PointSegmentDistance ( const FVector3d& x0,
const FVector3d& x1,
const FVector3d& x2
)

 Find distance x0 is from segment x1-x2
Public function Static float

PointTriangleDistance ( const FVector3f& x0,
const FVector3f& x1,
const FVector3f& x2,
const FVector3f& x3
)

 Find distance x0 is from triangle x1-x2-x3
Public function Static double

PointTriangleDistance ( const FVector3d& x0,
const FVector3d& x1,
const FVector3d& x2,
const FVector3d& x3
)

 Find distance x0 is from triangle x1-x2-x3
Public function Static bool

ShouldUseSpatial ( int ExactCells,
double CellSize,
double AvgEdgeLen
)

 Encodes heuristic for deciding whether it will be faster to use
Public function bool

Validate ( const FAxisAlignedBox3d& Bounds
)

  

Operators

  Type Name Description
Public function Const float

operator[] ( const FVector3i& Idx
)

  

Enums

  Type Name Description
Public enum EComputeModes The narrow band is always computed exactly, and the full Grid is always signed.  
Public enum EInsideModes What counts as "inside" the mesh.  

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