Class to check for collisions between two scenes. More...

#include <Inventor/collision/SoDualSceneCollider.h>

Public Member Functions
	SoDualSceneCollider ()
	Default constructor.

virtual	~SoDualSceneCollider ()

void	setMovingScene (SoPath *object, int max_triangles_per_leaf=0)
	Specifies the scene that will be moved or transformed.

void	setStaticScene (SoPath *scene, int max_triangles_per_leaf=0)
	Specifies the scene the moving scene is interacting with.

void	activate (SoTransform *transform)
	Specifies the transformation that will be watched.

virtual SbBool	checkCollision () const
	Checks if the current moving scene collides with the static scene.

virtual SbBool	searchNextIntersection () const
	Method called by checkCollision() for each pair of intersecting triangles found.

void	setMinEdgeLength (double minEdgeLength)
	Specifies the minimum length of a triangle edge.

double	getMinEdgeLength () const
	Returns the minimum length of a triangle edge.

void	enableMultiThread (bool enable)
	Use multiple threads to compute intersections.

bool	isMultiThreadEnabled () const
	Returns true if multithreaded computation is enabled.

Protected Member Functions
const SoPath *	getCollidingStaticPath () const
	Returns the path in the static scene of the current colliding shape.

const SoPath *	getCollidingMovingPath () const
	Returns the path in the moving scene of the current colliding shape.

void	getCollidingStaticTriangle (SbVec3f &v0, SbVec3f &v1, SbVec3f &v2) const
	Returns the coordinates of the current colliding triangle in the static scene.

void	getCollidingMovingTriangle (SbVec3f &v0, SbVec3f &v1, SbVec3f &v2) const
	Returns the coordinates of the current colliding triangle in the moving scene.

void	getCommonPoints (SbVec3f &p0, SbVec3f &p1) const
	Returns the coordinates of the two common points of the current pair of intersecting triangles.

virtual SbBool	isSensitiveStaticObject (const SoPath *object_path) const
	Tells if an object of the static scene is sensitive to collision detection or not.

virtual SbBool	isSensitiveMovingObject (const SoPath *object_path) const
	Tells if an object of the moving scene is sensitive to collision detection or not.

virtual void	staticTriangleListBuilt (int num_triangles) const
	Method called by setStaticScene() when the list of triangles in the static scene is built.

virtual void	staticLeafBuilt (int num_triangles) const
	Method called by setStaticScene() when a new leaf is stored in the static tree.

virtual void	movingTriangleListBuilt (int num_triangles) const
	Method called by setMovingScene() when the list of triangles in the moving scene is built.

virtual void	movingLeafBuilt (int num_triangles) const
	Method called by setMovingScene() when a new leaf is stored in the moving tree.

Detailed Description

Class to check for collisions between two scenes.

The SoDualSceneCollider class manages collisions, i.e., it checks the intersection of one scene with a second scene. Both scenes are tessellated into a list of triangles by using an SoCallbackAction and its addTriangleCallback method. An intersection occurs when a triangle of the first scene intersects a triangle of the second scene. For each pair of intersecting triangles some response methods are called. These response methods can be overridden, for instance,

to highlight the intersecting shape
to highlight the intersecting pair of triangles
to compute points common to the two scenes
to count the number of intersecting pairs of triangles
etc.

The SoDualSceneCollider references a static scene and a moving scene (with two SoPaths) and a transformation (with an SoTransform). The user scene graph must be organized such that the transformation will affect the moving scene during traversal. The static scene is specified by the method setStaticScene and the moving scene by the method setMovingScene.

The SoDualSceneCollider references a scene by storing its triangle list (see SoCallbackAction) and by building a database as a tree. This database spatially organizes the list of triangles in order to optimize the number of triangle intersection tests. Note that the SoDualSceneCollider does not monitor the scene graph. Any modifications to the Open Inventor nodes in the static scene or the moving scene are not reflected in the internal tree database unless setMovingScene or setStaticScene are called again by the application.

However SoDualSceneCollider watches for any modification to the given transformation. Each time the transformation changes, an intersection test is done between the two scenes by automatically calling checkCollision(). This method searches for pairs of intersecting triangles in an optimal way. For each pair of intersecting triangles found, the Boolean method searchNextIntersection() is called. By default this method returns FALSE, but in most cases, it will be overridden. If it returns FALSE, the process of searching intersecting triangles is stopped and checkCollision() returns TRUE. If searchNextIntersection returns TRUE, the process continues to search other pairs of intersecting triangles. If searchNextIntersection always returns TRUE, all pairs of intersecting triangles will be found. If the two scenes do not collide, searchNextIntersection is never called and checkCollision returns FALSE. When searchNextIntersection is overridden, some methods can be called to get information about the current pair of intersecting triangles:
getCollidingStaticPath(), getCollidingStaticTriangle(), getCollidingMovingPath(), getCollidingMovingTriangle(), and getCommonPoints().

In the static or moving scene, each internal node of the tree contains a bounding box while the leaf nodes contain triangles of the tessellation. The maximum number of triangles per leaf (max_triangles_per_leaf) is given as the second argument of the method setMovingScene and setStaticScene. Note how max_triangles_per_leaf affects the computation:

the smaller max_triangles_per_leaf, the deeper the tree.
the smaller max_triangles_per_leaf, the more memory the tree needs
the smaller max_triangles_per_leaf, the quicker the checkCollision() function becomes
the smaller max_triangles_per_leaf, the slower the setMovingScene/setStaticScene() functions become

A compromise must be chosen between the initial time to build the tree (setMovingScene/setStaticScene) and the time to check the collisions.

Depending on the total number of triangles and the value of max_triangles_per_leaf, the execution of setMovingScene/setStaticScene can take several seconds. The methods staticTriangleListBuilt/movingTriangleListBuilt and staticLeafBuilt/movingLeafBuilt have been defined and can be overridden to implement, for instance, a progress bar. However, note that the methods staticLeafBuilt/movingLeafBuilt are not called in linear time.

Collision checking will be faster using multiple threads. See the enableMultiThread() method.

Definition at line 112 of file SoDualSceneCollider.h.

Constructor & Destructor Documentation

◆ SoDualSceneCollider()

SoDualSceneCollider::SoDualSceneCollider ( )

Default constructor.

◆ ~SoDualSceneCollider()

virtual SoDualSceneCollider::~SoDualSceneCollider ( )

virtual

Member Function Documentation

◆ activate()

void SoDualSceneCollider::activate ( SoTransform * transform )

Specifies the transformation that will be watched.

When the transformation changes, collision detection computations are started. transform is the transformation node to watch. If NULL, the collision are not checked.

◆ checkCollision()

virtual SbBool SoDualSceneCollider::checkCollision ( ) const

virtual

Checks if the current moving scene collides with the static scene.

This method is automatically called when the transform node given to activate() is updated (or touched). Returns TRUE if the two scenes collide, FALSE otherwise.

◆ enableMultiThread()

void SoDualSceneCollider::enableMultiThread ( bool enable )

Use multiple threads to compute intersections.

This is faster when testing for collision against a large number of triangles. The computation will use the maximum number of threads supported on the processor.

IMPORTANT: When multithreaded computation is enabled, the searchNextIntersection(), is not necessarily called from the main thread. Therefore the code in searchNextIntersection() (and any methods called from it) must be thread-safe. As an example, GUI update calls outside the main thread are often not allowed.

Default is FALSE.

Since Open Inventor 9.6