de.grogra.vecmath.geom
Class MeshVolume

java.lang.Object
  de.grogra.vecmath.geom.VolumeBase
      de.grogra.vecmath.geom.MeshVolume

All Implemented Interfaces:

Volume, java.lang.Cloneable

Direct Known Subclasses:

MyMeshVolume

public class MeshVolume
extends VolumeBase
implements java.lang.Cloneable

This class represents a given Mesh as a Volume. It uses an octree in order to speed up the intersection computation; an octree cell contains a list of those polygons of the mesh which lie within the cell.

The algorithm for a single polygon-line intersection is an extension to general polygonal meshes (with convex, planar polygons) of the algorithm in the paper "Ray Tracing Triangular Meshes" of John Amanatides and Kin Choi. The algorithm uses Plücker coordinates to decide if a line intersects a polygon.

The mesh coordinates are specified in their own coordinate system. The transformation from world coordinates to mesh coordinates is implemented by worldToMesh. The advantage of this is that it is possible to create a set of copies of a MeshVolume using dup() which can then be shifted to another location using setTransformation(Matrix4d).

To set the data of a MeshVolume, both methods setMesh(de.grogra.vecmath.geom.Mesh) and setTransformation(javax.vecmath.Matrix4d) have to be invoked in this order.

Author:

Ole Kniemeyer

Field Summary

static int

MIN_CELL_OBJECTS Minimum number of polygons which have to be present in an octree cell so that it is considered for subdivision.

Constructor Summary

MeshVolume()

Method Summary

boolean	boxContainsBoundary(BoundingBox box, Tuple3d center, double radius, Variables temp) Returns true if the specified box contains (part of) the boundary surface of this volume.
void	computeFaceNormal(Intersection is, Vector3d normal) Compute the face normal of the triangle that was hit (is.face).
boolean	computeIntersections(Line line, int which, IntersectionList list, Intersection excludeStart, Intersection excludeEnd) Computes intersections between the boundary surface of this object and the specified line.
void	computeNormal(Intersection is, Vector3d normal) This method computes the unit normal vector of an intersection is which has been computed previously by the invocation of Volume.computeIntersections(de.grogra.vecmath.geom.Line, int, de.grogra.vecmath.geom.IntersectionList, de.grogra.vecmath.geom.Intersection, de.grogra.vecmath.geom.Intersection) on this volume.
void	computeTangents(Intersection is, Vector3d dpdu, Vector3d dpdv) This method computes the derivatives of the surface point (as function of the uv-coordinates, see Volume.computeUV(de.grogra.vecmath.geom.Intersection, javax.vecmath.Vector2d)) with respect to u and v at the intersection point.
void	computeUV(Intersection is, Vector2d uv) This method computes the uv-coordinates of an intersection point is which has been computed previously by the invocation of Volume.computeIntersections(de.grogra.vecmath.geom.Line, int, de.grogra.vecmath.geom.IntersectionList, de.grogra.vecmath.geom.Intersection, de.grogra.vecmath.geom.Intersection) on this volume.
boolean	contains(Tuple3d point, boolean open) Determines if the given point lies within this object.
MeshVolume	dup() Creates a duplicate of this mesh.
void	getExtent(Tuple3d min, Tuple3d max, Variables temp) Computes the extent of this volume, i.e., an axis-aligned bounding box between min and max.
Octree	getOctree()
int	getPolygonCount()
void	setMesh(Mesh mesh) Sets the mesh of this volume to the specified mesh.
void	setTransformation(Matrix4d meshToWorld) Sets the transformation from mesh coordinates to global world coordinates.

Methods inherited from class de.grogra.vecmath.geom.VolumeBase

addConvexIntersections, getId, operator$and, operator$com, operator$or, operator$sub, setId

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

MIN_CELL_OBJECTS

public static int MIN_CELL_OBJECTS

Minimum number of polygons which have to be present in an octree cell so that it is considered for subdivision.

Constructor Detail

MeshVolume

public MeshVolume()

Method Detail

boxContainsBoundary

public boolean boxContainsBoundary(BoundingBox box,
                                   Tuple3d center,
                                   double radius,
                                   Variables temp)

Description copied from interface: Volume

Returns true if the specified box contains (part of) the boundary surface of this volume. Otherwise, if box and boundary do not overlap, this method should return false, but may also return true if an exact computation would be too expensive or complicated.

Note that a box contains the boundary of a closed set S iff both have a non-empty intersection and the box is not contained in the open set of S.

Specified by:

boxContainsBoundary in interface Volume

Parameters:

box - bounding box

center - center coordinates of box

radius - radius of enclosing sphere

temp - has to be provided by the invoker, may be used in implementations

Returns:

true if box contains (part of) the boundary of this volume

computeFaceNormal

public void computeFaceNormal(Intersection is,
                              Vector3d normal)

Compute the face normal of the triangle that was hit (is.face). The normal vector is calculated as the cross product between the edge vectors of the triangle.

Parameters:

is - intersection between this volume and a ray

normal - output memory for computed normal vector

computeIntersections

public boolean computeIntersections(Line line,
                                    int which,
                                    IntersectionList list,
                                    Intersection excludeStart,
                                    Intersection excludeEnd)

Description copied from interface: Volume

Computes intersections between the boundary surface of this object and the specified line. The intersections are added to list in ascending order of distance (i.e., of Intersection.parameter), where the parameter has to lie between line.start and line.end. Implementations of this method must not clear or modify the existing intersections in list.

The parameter which has to be one of Intersection.ALL, Intersection.CLOSEST, Intersection.ANY. It determines if all intersections have to be added to the list, only the closest (minimal value of Intersection.parameter), or an arbitrary of the set of all intersections. Only in case of ALL, the return value of this method is precise.

If specific intersection points should be excluded from the list of computed intersections, they have to be specified in excludeStart and excludeEnd. The intersection point of excludeStart has to be the starting point of line, the intersection point of excludeEnd has to be the end point of line. The exclusion of intersections is a useful feature for ray-tracing, e.g., when a ray is re-emitted at an intersection point in another direction.

Specified by:

computeIntersections in interface Volume

Parameters:

line - a line

which - one of Intersection.ALL, Intersection.CLOSEST, Intersection.ANY, this determines which intersections have to be added to list

list - the intersections are added to this list

excludeStart - intersection at start point which shall be excluded, or null

excludeEnd - intersection at end point which shall be excluded, or null

Returns:

true iff the beginning of the line lies within the volume (i.e., if the line starts within the volume or enters the volume at the starting point); however note that the returned value is valid only if which == Intersection.ALL

computeNormal

public void computeNormal(Intersection is,
                          Vector3d normal)

Description copied from interface: Volume

This method computes the unit normal vector of an intersection is which has been computed previously by the invocation of Volume.computeIntersections(de.grogra.vecmath.geom.Line, int, de.grogra.vecmath.geom.IntersectionList, de.grogra.vecmath.geom.Intersection, de.grogra.vecmath.geom.Intersection) on this volume.

Specified by:

computeNormal in interface Volume

Parameters:

is - a previously computed intersection

normal - resulting unit vector is placed in here

computeTangents

public void computeTangents(Intersection is,
                            Vector3d dpdu,
                            Vector3d dpdv)

Description copied from interface: Volume

This method computes the derivatives of the surface point (as function of the uv-coordinates, see Volume.computeUV(de.grogra.vecmath.geom.Intersection, javax.vecmath.Vector2d)) with respect to u and v at the intersection point.

Specified by:

computeTangents in interface Volume

Parameters:

is - a previously computed intersection

dpdu - resulting derivative with respect to u

dpdv - resulting derivative with respect to v

computeUV

public void computeUV(Intersection is,
                      Vector2d uv)

Description copied from interface: Volume

This method computes the uv-coordinates of an intersection point is which has been computed previously by the invocation of Volume.computeIntersections(de.grogra.vecmath.geom.Line, int, de.grogra.vecmath.geom.IntersectionList, de.grogra.vecmath.geom.Intersection, de.grogra.vecmath.geom.Intersection) on this volume.

Specified by:

computeUV in interface Volume

Parameters:

is - a previously computed intersection

uv - resulting uv-coordinates are placed in here

contains

public boolean contains(Tuple3d point,
                        boolean open)

Description copied from interface: Volume

Determines if the given point lies within this object. If open is true, the interior of the volume is considered (the largest open set contained in the volume, i.e., excluding the boundary), otherwise the closure of the volume.

Specified by:

contains in interface Volume

Parameters:

point - a point in global world coordinates

open - consider open or closed set

Returns:

true iff point is an element of the set

dup

public MeshVolume dup()

Creates a duplicate of this mesh. The complete polygon data is simply referenced from the new duplicate, so no new data arrays are allocated. The duplicate can be shifted to another location using setTransformation(Matrix4d).

Returns:

a duplicate of this volume

getExtent

public void getExtent(Tuple3d min,
                      Tuple3d max,
                      Variables temp)

Description copied from interface: Volume

Computes the extent of this volume, i.e., an axis-aligned bounding box between min and max.

Specified by:

getExtent in interface Volume

Parameters:

min - minimum coordinates of bounding box are placed in here

max - maximum coordinates of bounding box are placed in here

temp - has to be provided by the invoker, may be used in implementations

getOctree

public Octree getOctree()

getPolygonCount

public int getPolygonCount()

setMesh

public void setMesh(Mesh mesh)

Sets the mesh of this volume to the specified mesh. All data is copied, no persistent reference to mesh is made. The method setTransformation(javax.vecmath.Matrix4d) has to be invoked afterwards to specify the global coordinate transformation.

Parameters:

mesh - a mesh

setTransformation

public void setTransformation(Matrix4d meshToWorld)

Sets the transformation from mesh coordinates to global world coordinates.

Parameters:

meshToWorld - transformation matrix