The document summarizes the core objects in OGRE, an open source graphics rendering engine. It describes the root object which initializes other core systems like the scene manager and rendering system. The scene manager handles scene contents and rendering. The resource manager loads shared resources like textures and meshes. Materials control how objects are rendered with properties like textures. Entities use meshes and materials to represent movable objects in a scene.

1. OGRE (v1.10)
The Core Objects
王聖川
2017/9/21

2. Core Objects Diagram

3. Core Objects
Root: organizer, facilitator, to deal with scene
manager, rendering systems and render widnows.
Scene manager: about contents of scene.
Resource manager: for geometries, textures,
fonts, …
Rendering: for low-level end of rendering pipeline.
Plugins … to be extended, extended, and extended.

4. Root
Entry point of OGRE system. First created, last
destroyed.
Obtain pointers to systems: SceneManager,
RenderSystem, …
Root->startRendering(), enter continuous
rendering loop.

5. RenderSystem
Abstract class for underlying 3D (rendering) API.
Subclass: D3DRenderSystem, GLRenderSystem, …
Initialization in Root::initialise(), then
Root::getRenderSystem() to obtain.
SceneManager handles all high-level rendering
tasks. Only access RenderSystem for advanced
features necessary.

6. SceneManager
Charge of scene contents. Organizes cameras,
movable objects, lights, materials, and for world
(static) geometry.
When rendering, sends the scene to RenderSystem.
Setup scene (via input scene file), and dynamically
modify scene via FrameListener.
Subclass for different scene type:
BspSceneManager optimizes indoor levels via binary space
partition tree.

7. ResourceGroupManager
Hub for reusable resources. Implement
ResourceManager objects for different resource
types (TextureManager, MeshManager, …).
Resource is loaded once, shared throughout OGRE.
Searching in multiple search paths or compressed archives.
Singleton implementation.
Loading API is called automatically, yet you can
access manager (TextureManager) for pre-loading
purposes.

8. Mesh
Represents a discrete model, typically small on
world scale. Assumed for movable objects.
Managed by MeshManager (.mesh file).
Composed of SubMesh objects (for different parts).
Loaded with defined materials automatically.
Manually create: MeshManager::createManual().
Basis for movable object (called Entity).
Can be animated.

9. Entity
An instance of a movable object.
Based on Mesh, multiple entities can be based on
the same mesh.
Creation: SceneManager::createEntity(entity-name,
mesh-name). Mesh is loaded only once.
SubEntity: 1 vs. 1 matching SubMesh. Accessed by
Entity::getSubEntity().
Entities automatically use default materials. Material can be
changed per entity basis, call SubEntity::setMaterialName().
Attach to SceneNode to become part in the scene.
Hierarchical relationship between entities via scene nodes.

10. Material
Controls how objects are rendered.
Specify: surface properties (reflectance), texture layers
(which image, filtering), special effects (environmental
mapping), …
Setup: MaterialManager::create(), or by material
scripts (runtime loaded).
SceneManager manages existing material list.
Default properties,
MaterialManager::getDefaultSettings() :
ambient reflectance = white, diffuse reflectance = white,
specular reflectance = back, …, no texture layer, depth buffer
checking = on, depth buffer writing = on, …, bilinear texture
filtering.

11. Overlay
Render 2D/3D elements on top of screen (heads-
up displays, menu, status, …).
Creation: SceneManager::createOverlay() or by .overlay
script file.
Show multiple overlays at once following their Z-orders.
Manually initialization.
Need to call SceneManager::addRenderQueueListener() per
scene manager.
Designed for non-interactive screen elements.
Trays system (or CEGui, MyGUI, libRocket) for GUI solution.

12. Overlay 2D Elements
OverlayElement class abstracts 2D elements.
Subclasses for user-defined custom control element.
OverlayContainer (inherits OverlayElement),
contains (groups) OverlayElement objects.
OverlayManager to create specific overlay
elements.
OverlayManager::getSingleton().createOverlayElement(“Pa
nel”, “myNewPanel”); for panel container.
Allows plugins to register new types of OverlayElement.
2D coordinates: pixel mode and relative mode.