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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

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

   
Name TSweepingMeshSDF
Type class
Header File /Engine/Source/Runtime/GeometryCore/Public/Implicit/SweepingMeshSDF.h
Include Path #include "Implicit/SweepingMeshSDF.h"

Syntax

template<class TriangleMeshType, bool bScalarCellSize>  
class TSweepingMeshSDF

Constructors

Name Remarks Include Path Unreal Specifiers

TSweepingMeshSDF ( const TriangleMeshType* Mesh,
CellSizeType InCellSize,
TMeshAABBTree3< TriangleMeshType >* Spatial
)

   Implicit/SweepingMeshSDF.h  

Enums

Public

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

Typedefs

Name Type Remarks Include Path
CellSizeType std::conditional_t< bScalarCellSize, float, FVector3f > Type to use for CellSize. Implicit/SweepingMeshSDF.h
CellSizeTyped std::conditional_t< bScalarCellSize, double, FVector3d > Type to use for CellSize, but in double precision. Implicit/SweepingMeshSDF.h

Variables

Public

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

Functions

Public

Name Remarks Include Path Unreal Specifiers

float At ( int I,
int J,
int K
) const

   Implicit/SweepingMeshSDF.h  

FVector3f CellCenter ( int I,
int J,
int K
) const

   Implicit/SweepingMeshSDF.h  

bool Compute ( FVector3f InGridOrigin,
FVector3i InDimensions
)

 Compute the SDF with exactly specified grid origin and dimensions Implicit/SweepingMeshSDF.h  

bool Compute ( FAxisAlignedBox3d Bounds
)

 Compute the SDF enclosing the given bounds, with a 'safe' buffer zone Implicit/SweepingMeshSDF.h  

FVector3i Dimensions()

   Implicit/SweepingMeshSDF.h  

void Empty()

 Empty out all computed result data (leaves input data alone) Implicit/SweepingMeshSDF.h  

const FDenseGrid3i & GetClosestTriGrid()

   Implicit/SweepingMeshSDF.h  

const FDenseGrid3i & GetIntersectionsGrid()

   Implicit/SweepingMeshSDF.h  

float GetValue ( FVector3i Idx
) const

   Implicit/SweepingMeshSDF.h  

TTriLinearGridInterpolant< FDenseGrid3f, InterpolantRealType, bScalarCellSize > MakeInterpolant()

 Make an interpolating sampler of the sdf data. Note the lifetime is dependent on this class. Implicit/SweepingMeshSDF.h  

void SetCellSize ( float InCellSize
)

   Implicit/SweepingMeshSDF.h  

bool Validate ( const FAxisAlignedBox3d& Bounds
)

   Implicit/SweepingMeshSDF.h  

Static

Name Remarks Include Path Unreal Specifiers

static float GetDiagLength ( CellSizeType CellSize
)

   Implicit/SweepingMeshSDF.h  

static float GetDim ( CellSizeType CellSize,
int32 Axis
)

   Implicit/SweepingMeshSDF.h  

static double GetDim ( CellSizeTyped CellSize,
int32 Axis
)

 Helper methods to access CellSize in either scalar or vector mode. Implicit/SweepingMeshSDF.h  

static bool IsValid ( CellSizeType CellSize
)

   Implicit/SweepingMeshSDF.h  

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) Implicit/SweepingMeshSDF.h  

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. Implicit/SweepingMeshSDF.h  

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

 Find distance x0 is from segment x1-x2 Implicit/SweepingMeshSDF.h  

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

 Find distance x0 is from segment x1-x2 Implicit/SweepingMeshSDF.h  

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

 Find distance x0 is from triangle x1-x2-x3 Implicit/SweepingMeshSDF.h  

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

 Find distance x0 is from triangle x1-x2-x3 Implicit/SweepingMeshSDF.h  

static bool ShouldUseSpatial ( int ExactCells,
double CellSize,
double AvgEdgeLen
)

 Encodes heuristic for deciding whether it will be faster to use Implicit/SweepingMeshSDF.h  

static CellSizeType UnitCellSize()

 Unit cube, in CellSizeType. Implicit/SweepingMeshSDF.h  

Operators

Name Remarks Include Path Unreal Specifiers

float operator[] ( const FVector3i& Idx
) const

   Implicit/SweepingMeshSDF.h  

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