MTesselationParams Class Reference

#include <MTesselationParams.h>

Class Description

Tesselation parameters.

This class provides control over the tesselation operation. This class is meant to be used in conjunction with the tesselate method of MFnNurbsSurface.

The tesselation operation works by building an initial mesh and then refining that mesh until certain subdivision criteria are met. This class provides control over both the method of construction of the initial mesh and also the criteria for subsequent refinement. The initial tesselation is specified by the polygon output type, and the isoparm type. The secondary tesselation (or subdivision) is specified by the tesselation format.

Output types The output type can be specified as either kTriangles or kQuads. If triangles are specified then all the polygons in the initial mesh will be triangles. If quads are specified then whenever possible the polygons will be quads.

Isoparm type The isoparm type specifies how the initial mesh is to be built.

• kSurface3DDistance A set of isoparams over entire surface, a specified 3d-distance "udist" apart
• kSurface3DEquiSpaced A set of "unum" isoparams over entire surface, equally spaced in 3d
• kSurfaceEquiSpaced A set of "unum" isoparams over entire surface, equally spaced in u
• kSpanEquiSpaced A set of "unum" isoparams per surface u-span, equally spaced in u

Tesselation format The subdivision criteria for refinement of the initial mesh is specified as one of three formats;

• kTriangleCountFormat the specified triangle count is used as a rough estimate of the triangles produced in the tesselation.
• kGeneralFormat specify which subdivisions types are to be used in the tesselation. For each subdivision type the corresponding parameters must be set.
• kStandardFitFormat Tessellate surface with standard fit ratios. The parameters for this type of refinement are StdChordHeightRatio, StdFractionalTolerance, StdMinEdgeLength, and Std3DDelta.

Subdivision flags If the tesselation format is general then you can choose which criteria you would like to use in the tesselation. For each criterion, there is an "use" flag (in other words, is this used?) together with the data for the criterion.

Examples:

Public Types
enum	TessFormat { kTriangleCountFormat, kStandardFitFormat, kGeneralFormat }
	Tesselation formats. More...
enum	PolyType { kTriangles, kQuads }
	Types of polygons to use in the result. More...
enum	IsoparmType { kSurface3DDistance, kSurface3DEquiSpaced, kSurfaceEquiSpaced, kSpanEquiSpaced }
	Isoparm types. More...
enum	SubdivisionType {   kUseFractionalTolerance, kUseChordHeightRatio, kUseMinEdgeLength, kUseMaxEdgeLength,   kUseMaxNumberPolys, kUseMaxSubdivisionLevel, kUseMinScreenSize, kUseMaxUVRectangleSize,   kUseTriangleEdgeSwapping, kUseRelativeTolerance, kUseEdgeSmooth, kLastFlag }
	Subdivision flags. More...

Public Member Functions
	MTesselationParams (TessFormat format=kStandardFitFormat, PolyType=kTriangles)
	Constructor. More...
	MTesselationParams (const MTesselationParams &)
	Copy Constructor.
	~MTesselationParams ()
	Destructor.
void	setFormatType (TessFormat type)
	Sets the tesselation format. More...
void	setOutputType (PolyType type)
	Specifies the type of polygons in the tesselated object. More...
void	setTriangleCount (int)
	Sets the approximate number of triangles for the tesselated object when the format is kTriangleCountFormat. More...
void	setStdChordHeightRatio (double)
	Sets the chord height ratio which is used when the tesselation format is kStandardFitFormat. More...
void	setStdFractionalTolerance (double)
	Sets the fractional tolerance which is used when the tesselation format is kStandardFitFormat. More...
void	setStdMinEdgeLength (double)
	Sets the minimum edge length which is used when the tesselation format is kStandardFitFormat. More...
void	setSubdivisionFlag (SubdivisionType type, bool use)
	Sets the types of subdivision used when the tesselation format is general. More...
void	setFitTolerance (double)
	Sets the absolute fit tolerance. More...
void	setChordHeightRatio (double)
	Sets the chord height ratio. More...
void	setMinEdgeLength (double)
	Sets the minimum edge length. More...
void	setMaxEdgeLength (double)
	Sets the maximum edge length. More...
void	setMaxNumberPolys (int)
	Sets the maximum number of polygons. More...
void	setMaxSubdivisionLevel (double)
	Sets the maximum subdivision level. More...
void	setMinScreenSize (double, double)
	If polygons are smaller than the specified screen size then the subdivision will not proceed. More...
void	setWorldspaceToScreenTransform (MMatrix &)
	The transformation matrix used in the minimum screen size test for subdivision. More...
void	setMaxUVRectangleSize (double, double)
	Sets the maximum polygon size in uv-space for secondary tesselation. More...
void	setRelativeFitTolerance (double)
	Sets the relative fit tolerance. More...
void	setEdgeSmoothFactor (double)
	Sets the edge smoothness factor used for the Edge Smooth secondary tesselation criteria. More...
void	set3DDelta (double)
	Sets the fraction of the box diagonal to be used as 3-d spacing for u- and v-isoparams on face/surface to make up the initial grid for the mesh. More...
void	setUIsoparmType (IsoparmType type)
	Sets the u-isoparm type to be used in the initial tesselation. More...
void	setVIsoparmType (IsoparmType type)
	Sets the v-isoparm type to be used in the initial tesselation. More...
void	setUNumber (int count)
	This is the number of u isoparms used in the initial tesselation. More...
void	setVNumber (int count)
	This is the number of v isoparms used in the initial tesselation. More...
void	setBoundingBoxDiagonal (double distance)
	Sets the diagonal distance of the bounding box of the surface. More...
void	setUDistanceFraction (double value)
	Sets the fraction of the 3D surface bounding box diagonal for the kSurface3DDistance isoparm type. More...
void	setVDistanceFraction (double value)
	Sets the fraction of the 3D surface bounding box diagonal for the kSurface3DDistance isoparm type. More...
MTesselationParams &	operator= (const MTesselationParams &rhs)
	Assignment operator. More...

Static Public Member Functions
static const char *	className ()
	Returns the name of this class. More...

Friends
class	MFnNurbsSurface

Member Enumeration Documentation

enum TessFormat

Tesselation formats.

Enumerator
kTriangleCountFormat
kStandardFitFormat
kGeneralFormat

enum PolyType

Types of polygons to use in the result.

Enumerator
kTriangles
kQuads

enum IsoparmType

Isoparm types.

Enumerator
kSurface3DDistance
kSurface3DEquiSpaced
kSurfaceEquiSpaced
kSpanEquiSpaced

enum SubdivisionType

Subdivision flags.

Enumerator
kUseFractionalTolerance
kUseChordHeightRatio
kUseMinEdgeLength
kUseMaxEdgeLength
kUseMaxNumberPolys
kUseMaxSubdivisionLevel
kUseMinScreenSize
kUseMaxUVRectangleSize
kUseTriangleEdgeSwapping
kUseRelativeTolerance
kUseEdgeSmooth
kLastFlag

Constructor & Destructor Documentation

MTesselationParams	(	MTesselationParams::TessFormat	format = kStandardFitFormat,
		MTesselationParams::PolyType	outputType = kTriangles
	)

Constructor.

Creates a tesselation parameter object.

The default values for an MTesselationParam object are as follows:

• tesselation format kStandardFit
• output type kTriangles
• Standard Fit defaults

• StdChordHeightRatio = 0.1
• StdFractionalTolerance = 0.01
• StdMinEdgeLength = 0.001
• Std3DDelta = 0.1

• U,V isoparm based parameters

• UIsoParmType = kSurface3DDistance;
• VIsoParmType = kSurface3DDistance;
• UNumber = 4.0;
• VNumber = 4.0;
• fUDistanceFraction = 0.1;
• fVDistanceFraction = 0.1;

Parameters

[in]	format	The type of tesselation to be performed
[in]	outputType	Specifies whether polygons will all be triangles

Member Function Documentation

void setFormatType

(

MTesselationParams::TessFormat

format

)

Sets the tesselation format.

The tesselation format is used in the secondary tesselation stage to specify the subdivision criteria used in refining the initial mesh.

Parameters

[in]

format

the subdivision format. See the class description for list of format types and descriptions.

void setOutputType

(

MTesselationParams::PolyType

outputType

)

Specifies the type of polygons in the tesselated object.

The output type can be specified as either triangles or quads. If triangles are specified then all the polygons in the tesselated object will be triangles. If quads are specified then whenever possible the polygons will be quads.

Parameters

[in]

outputType

the type of polygon in the tesselated object

void setTriangleCount

(

int

count

)

Sets the approximate number of triangles for the tesselated object when the format is kTriangleCountFormat.

Parameters

[in]

count

The approximate number of triangular polygons in the tesselated object

void setStdChordHeightRatio

(

double

value

)

Sets the chord height ratio which is used when the tesselation format is kStandardFitFormat.

Parameters

[in]

value

the chord height ration value to be set

void setStdFractionalTolerance

(

double

value

)

Sets the fractional tolerance which is used when the tesselation format is kStandardFitFormat.

The fractional tolerance is the fraction of box diagonal to be used as absolute 3-d fit tolerance. Suggested value: 0.01

Parameters

[in]

value

the fractional tolerance value to be set

void setStdMinEdgeLength

(

double

value

)

Sets the minimum edge length which is used when the tesselation format is kStandardFitFormat.

min_edge_fraction Fraction of box diagonal to be used as minimum 3-d edge length. Suggested value: 0.0001

Parameters

[in]

value

the minimum edge length to be set

void setSubdivisionFlag	(	MTesselationParams::SubdivisionType	subType,
		bool	use
	)

Sets the types of subdivision used when the tesselation format is general.

This method allows you to set the types of subdivision to be performed after the initial mesh is created. The use flag specifies whether to use the given subdivision type in the secondary tesselation.

Parameters

[in]	subType	the subdivision type to be specified
[in]	use	specifies whether to use subType subdivision

void setFitTolerance

(

double

value

)

Sets the absolute fit tolerance.

This value is used when the subdivision criteria kUseFractionalTolerance has been set.

NOTE: The maya renderer uses this subdivision criteria for chord height.

Parameters

[in]

value

the new absolute fit tolerance value to be set

void setChordHeightRatio

(

double

value

)

Sets the chord height ratio.

This value is used when the subdivision criteria kUseChordHeightRatio has been set.

NOTE: The maya renderer uses relative fit tolerance for the chord height ration subdivision criteria.

Parameters

[in]

value

the new chord height ratio value to be set

void setMinEdgeLength

(

double

value

)

Sets the minimum edge length.

This value is used when the subdivision criteria kUseMinEdgeLength has been set.

Parameters

[in]

value

the new minimum edge length value to be set

void setMaxEdgeLength

(

double

value

)

Sets the maximum edge length.

This value is used when the subdivision criteria kUseMaxEdgeLength has been set.

Parameters

[in]

value

the new maximum edge length value to be set

void setMaxNumberPolys

(

int

value

)

Sets the maximum number of polygons.

This value is used when the subdivision criteria kUseMaxNumberPolys has been set.

Parameters

[in]

value

the new maximum number of polygons value to be set

void setMaxSubdivisionLevel

(

double

value

)

Sets the maximum subdivision level.

This value is used when the subdivision criteria kUseMaxSubdivisionLevel has been set.

Parameters

[in]

value

the new maximum subdivision level value to be set

void setMinScreenSize	(	double	x,
		double	y
	)

If polygons are smaller than the specified screen size then the subdivision will not proceed.

These values are used when the subdivision criteria kUseMinScreenSize has been set.

Parameters

[in]	x	the width value to compare against
[in]	y	the height value to compare against

void setWorldspaceToScreenTransform

(

MMatrix &

value

)

The transformation matrix used in the minimum screen size test for subdivision.

This value is used when the subdivision criteria kUseMinScreenSize has been set.

Parameters

[in]

value

The world-space transformation matrix

void setMaxUVRectangleSize	(	double	u,
		double	v
	)

Sets the maximum polygon size in uv-space for secondary tesselation.

Polygons will be greater than the specified size.

Parameters

[in]	u	horizontal screen space size
[in]	v	vertical screen space size

void setRelativeFitTolerance

(

double

value

)

Sets the relative fit tolerance.

This value is used when the subdivision criteria kUseRelativeTolerance has been set.

NOTE: The maya renderer uses this subdivision criteria for chord height ratio. To match the value that the render tesselator uses, use 1.0 - value.

Parameters

[in]

value

the new relative fit tolerance value to be set

void setEdgeSmoothFactor

(

double

smoothness

)

Sets the edge smoothness factor used for the Edge Smooth secondary tesselation criteria.

The value should be 0 (not smooth) to 1 (very smooth).

NOTE: the maya renderer uses a value of 0.95 as the edge smoothness factor.

Parameters

[in]

smoothness

a factor from 0(not smooth) to 1(very smooth) indicating nurbs-edge smoothness

void set3DDelta

(

double

delta

)

Sets the fraction of the box diagonal to be used as 3-d spacing for u- and v-isoparams on face/surface to make up the initial grid for the mesh.

This is used when the tesselation format is kStandardFitFormat.

NOTE: the maya renderer uses a default value of 0.1 for this value.

Parameters

[in]

delta

the fractional spacing factor, a value between 0 and 1

void setUIsoparmType

(

IsoparmType

uValue

)

Sets the u-isoparm type to be used in the initial tesselation.

Parameters

[in]

uValue

the u-isoparm type

void setVIsoparmType

(

IsoparmType

vValue

)

Sets the v-isoparm type to be used in the initial tesselation.

Parameters

[in]

vValue

the v-isoparm type

void setUNumber

(

int

count

)

This is the number of u isoparms used in the initial tesselation.

This value is only used for kSurface3DEquiSpaced, kSurfaceEquiSpaced, and kSpanEquiSpaced isoparm types.

Note that in the resultant tessellation, any duplicate vertices and edges (eg at periodic boundaries) will be replaced with shared common vertices and edges.

Parameters

[in]

count

the number of u isoparms

void setVNumber

(

int

count

)

This is the number of v isoparms used in the initial tesselation.

This value is only used for kSurface3DEquiSpaced, kSurfaceEquiSpaced, and kSpanEquiSpaced isoparm types.

Note that in the resultant tessellation, any duplicate vertices and edges (eg at periodic boundaries) will be replaced with shared common vertices and edges.

Parameters

[in]

count

the number of v isoparms

void setBoundingBoxDiagonal

(

double

distance

)

Sets the diagonal distance of the bounding box of the surface.

Parameters

[in]

distance

the diagonal bounding box distance

void setUDistanceFraction

(

double

value

)

Sets the fraction of the 3D surface bounding box diagonal for the kSurface3DDistance isoparm type.

The value is 0.0 for other types.

Parameters

[in]

value

the bounding box distance fraction to set

void setVDistanceFraction

(

double

value

)

Sets the fraction of the 3D surface bounding box diagonal for the kSurface3DDistance isoparm type.

The value is 0.0 for other types.

Parameters

[in]

value

the bounding box distance fraction to set

MTesselationParams & operator=

(

const MTesselationParams &

rhs

)

Assignment operator.

Parameters

[in]

rhs

the tesselation parameter to copy

Returns

A reference to the copied tesselation parameter.

const char * className ( )

static

Returns the name of this class.

Returns

Name of this class.

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The documentation for this class was generated from the following files:

• MTesselationParams.h
• MTesselationParams.cpp