OGRE v2.1 manual - Technical Overview

1. OGRE (v2.1)
Technical Overview
王聖川
2017/9/23

2. Overview
ArrayMemoryManager, base system for SoA (structure of
arrays).
NodeMemeryManager: manages multiple
NodeArrayMemoryManager (one per parent level).
Store Transform.
ObjectDataMemoryManager: manages multiple
ObjectDataArrayMemoryManager (one per render queue).
Store ObjectData.

3. SIMD Coherence
SSE2 single precision build, process/pack 4
nodes/entities at a time.
Always allocate memory for 4 objects (even handling with
1~3 objects). Default PACKED_ARRAY_REALS = 4.
Set default sane values (identity quaternion, matrix and
dummy pointer) to prevent NaN.
Memory manager uses concept of slots.
4 slots make a block.
LIFO (last in first out) for best performance.
If slot is dropped without LIFO order, it is recorded in
another list for later reuse.

4. Memory Cleanup
When non-LIFO order released slots are too many,
performing cleanup to move memory to keep it
contiguous again.
Example:
Too many released:
Cleaup:

5. Memory Pre-allocate
Pre-allocate a fix amount of slots at initialization.
When pre-allocate limit is reached:
Buffer resizing, pointers to the previous slots become invalid.
Nodes, MovableObjects internal pointers are automatically
updated.
If hard limit is reached, throw exception.
How to configure? Not implemented… (|||ﾟдﾟ)

6. No More
RenderTarget::update
OGRE 2.x removes RenderTarget::update(), cause
render scene update is split in 2 stages (cull and
render).
Try Compositor! Compositor! And Compositor!
If you insist low-level developing with render
targets, read CompositorPassScene::execute().

7. Port 1.x to 2.0
Main changes:
Compositor: not for post-processing only. Design how you
render the scene.
Many listeners are removed (for performance). Most
important listener left is CompositorWorkspaceListener.
Create a custom rendering pass via CompositorPassProvider.
Light must be attached to SceneNode.
SceneNodes and Cameras should not be modified after
SceneManager::updateAllTransforms(). Use assertions for
debugging.

8. Port 2.0 to 2.1
Main changes: v2 objects and Hlms (High-Level
Material System).
V2 object, Item: considerably faster than v1::Entity.
v1::Entity is still useful (good performance).
Render 100 different meshes, v1::Entities need 100 draw
calls while Items can drop to 1 draw call! How???
In OGRE 2.1, should use HlmsDatablock to replace
Material.
Manipulating Materials, can change to use Hlms scripts.
Use Hlms, setup parameters (texture, color, …) and then
Hlms analyzes it and generates shaders for rendering.
To design your custom Hlms, study templates of Hlms
implementation (need more documents …).