Rendering Engine Basics CS 446: RealTime Rendering

1
Rendering Engine Basics CS 446 Real-Time
Rendering Game Technology

• David Luebke
• University of Virginia

2
Demo Time

• Ewen Cheslack-Postava ATI 1800XT demos

3
The Rendering Engine

• Job render the scene (duh)
• From camera
• From other viewpoints (why?)

4
The Rendering Engine

• Job render the scene (duh)
• From camera
• From other viewpoints (why?)
• Shadow maps
• Render to texture e.g. for reflection maps
• Multiple times from the same viewpoint (why?)

5
The Rendering Engine

• Job render the scene (duh)
• From camera
• From other viewpoints
• Multiple times from the same viewpoint (why?)
• Multipass shaders with blending (show Enemy
  Territories video)
• Z-only pass
• Deferred shading
• With different settings (why?)

6
The Rendering Engine

• Job render the scene (duh)
• From camera
• From other viewpoints
• Multiple times from the same viewpoint
• With different settings (why?)
• May not need color (Z-only pass, shadow maps)
• Low-res texture and/or geometry LOD may be okay
• May need different render target, resolution,
  viewport, GL state

7
Rendering Engine Concepts

• Need to support several ways of accessing scene
• Functional/relational/hierarchical
• The scene graph
• Spatial
• For example, for culling or (rough) front-to-back
  sorting
• Material
• Sorted by state for efficient issue to GPU
• Need to support updating object pose, deformation

8
Rendering Engine Concepts

• Need to support several ways of accessing scene
• Functional/relational/hierarchical
• Spatial
• Material
• Interacts with other components!
• Physics engine (e.g., collision detection)
• Animation engine (e.g., IK, animation cycles)
• AI engine (e.g., sightlines)

9
The Scene Graph

• A hierarchy representing objects and
  relationships
• The gun on the turret on the tank
• The hand on the forearm on the upper arm on the
  trunk
• The mouse on the cheese on the table
• Typically represented as a DAG (whats that?)
• Arcs represent relationships, sometimes xforms
• Nodes represent objects, groupings of objects,
  sometimes properties of objects
• What kind of things might nodes represent?

10
Scene Graph Node Examples

• Objects
• Groups of objects
• LOD selectors
• Animation effectors
• Flipbook animation selectors
• Transform drivers
• Deformers
• Skeletal animation players

• Transforms
• Useful state
• Bounding boxes, partitions
• Graphics state
• Which textures, shaders bound
• Material
• Other state - glEnable(GL_FOO)
• Raw geometry
• Vertices and triangles

Note often actual geometry only exists at leaves
11
Scene Graph Traverals

• Classical use of scene graph
• Traverse in depth-first fashion
• Apply effects of action nodes when reached
• LOD selectors, animation effectors
• Push/pop matrices when reach/leave xform nodes
• Issue geometry as reached
• Not very efficient for complex scenes (why?)
• Unnecessary pushing/popping
• Constantly switching graphics state
• No spatial organization
• Lots of recalculation for multiple passes