Scene

Overview

The Scene defines a flat collection of SceneObjects and fully represents the virtual environment. SceneObjects may be a surgical tool, a tissue, OR table, a leg, light, or even non-visual objects. A simple visual object can be added to the Scene as:

auto scene = std::make_shared<Scene>("MyScene");

auto myObject = std::make_shared<SceneObject>("MyObject");
auto visuals = myObject->addComponent<VisualModel>();
// visuals->setGeometry(<my geometry here>);
scene->addSceneObject(myObject);

iMSTK contains an entity-component (ECS) model that is still a work in progress. Whilst objects/entities represent whole concepts such as a tool or table. A component represents a swappable part of the object/entity such as the legs of a table or reciprocation of a saw tool. ECS's are common in many game engines for modularity and flexibility. One may subclass Component or Behaviour to add new functionality.

Entity/SceneObject

Whilst iMSTK is in the middle of an ECS refactor. The SceneObject represents and object in the scene. It stems from Entity providing an optional visual geometry and a TaskGraph to introduce TaskNode steps to the scene TaskGraph that is run during advacement of the scene.

Many types stem from SceneObject eventually to be moved to Components, here's a full list of those types:

• SceneObject: Provides an object with a visual geometry and empty virtual update function. Geometry is optional.
• CollidingObject: Provides an object with both visual and colliding geometry.
• PbdObject: Provides a PbdModel governing its physics.
• RigidObject: Provides a RigidBodyModel governing its physics.
• RigidObject2: Provides a RigidBodyModel2 governing its physics.
• FemDeformableObject: Provides a FemModel governing its physics.
• SPHObject: Provides a SPHModel governing i
• LevelSetDeformableObject: Provides a LevelSetModel governing its physics.

Component

An entity (SceneObject base) is made of many components. A component represents a data-only part of an entity. It does no function, has an initialization, and a reference to the entity it is part of. Components can be placed on/off entities/objects whenever. One can extend to hold relevant data and use elsewhere.

class MyComponent : public Component
{
public:
    Mat4d myTransform = Mat4d::Identity();
};

Behaviour

A Behaviour is a Component that has function. Generally only recommend for small independent bits of logic. Anything that involves multiple components, call order, lots of communication, or multiple Entity's may need its own system such the VTKRenderer or Scene. Alternatively the TaskGraph can be used.

class MyBehaviour : public Behaviour
{
public:
    void update() override {} // Called per SceneManager::update (Scene::advance)
    void visualUpdate() override {} // Called per VTKViewer::update
};

It is safe to assume the physics system is complete before entering any components. See more in the computational flow section.

Initialization of the Scene

Initialization of the scene and the things in it is done as follows:

• Initialize Scene
  • Initialize all SceneObject's of the Scene
  • Initialize all Component's of every SceneObject in the Scene
    • If any Components are introduced during Component::initialize, they are initialized too
  • Initialize all the DynamicalModel's used by SceneObject's in the Scene
  • Build the TaskGraph of the Scene

Advancement of a Scene

Normally the Scene would be given to the SceneManager to run and VTKViewer to render. These would be apart of SimulationManager. However, one is able to advance the scene at their own timestep by using:

scene->initialize(); // Must be initialized first
scene->advance(0.001); // Timestep to advance by

Update order is as follows:

• Update all SceneObjects and Behaviours on them.
• Update all TaskGraph nodes (including physics steps).