The Rendering Pipeline

1
The Rendering Pipeline

• JI HYE SON
• 2003. 12. 08

2
Outline

• Introduction
• The Graphics Rendering Pipeline
• Three functional stages
• Example
• Bottleneck
• Optimization
• The Haptics Rendering Pipeline

3
Introduction

• For smooth simulations
• Need to display at least 24, or, better 30
  frame/secs
• Total latency is not over 100msec
• Low latency and fast graphics require a VR engine
  that has a powerful computer architecture
• These architectures are designed around a
  rendering pipeline
• Rendering
• The process of converting the 3D geometrical
  models populating a virtual world into a 2D scene
  presented to the user

4

• The Graphics Rendering Pipeline

5
Three functional stages

• Graphics rendering has three functional stages.

User input
Video controller
6
Application stage

• Implemented in software
• Run on several CPUs
• Read the world geometry database the users
  input
• Basic operations
• take care of users input
• acceleration algorithm
• Output 3D geometric primitives (polygons, meshes)

7
Geometry stage

• Implemented in software or hardware
• Run on the geometry engines
• Basic operations
• Output 2D geometric primitives (2D polygons)

8
Rasterizer stage

• Implemented in hardware
• Convert the vertex information output into pixel
  information needed by the video display
• Basic operations
• Scan conversion (rasterization)
• Z-buffering
• Anti-aliasing
• Texture mapping
• Output pixel values

9
Example

• Geometry rasterizer stages in HP Visualize fx
  card

10
Bottleneck

• One of the three stages will be the slowest
• gt bottleneck stage
• CPU-limited
• In the application stage
• Transform-limited
• In the geometry stage
• Fill-limited
• In the rasterizer stage

11
Optimization (1/2)

• Application stage CPU-limited
• Replace the CPU with a faster one or add another
  CPU
• Reduce CPUs load
• Reduce the scene complexity by using 3D models
  with a lower polygonal count
• Optimize the simulation software
• Geometry stage Transform-limited
• Need to look at the computation load assigned to
  the GEs
• Reduce the number of virtual light sources
• Use the Simple shading mode
• Use the type of polygon for which its rendering
  hardware was optimized

12
Optimization (2/2)

• Rasterizer stage fill-limited
• Reduce the number of pixel in the displayed image
• Reduce the size of the display window
• Reduce the window resolution

13

• The Haptics Rendering Pipeline

14
The Haptics Rendering Pipeline
Collision detection stage
Force computation stage
Tactile computation stage
Compute force
Force smoothing
Force mapping
User input
Haptic interface
CPU1
Haptic texturing
CPU2
15
The stages of the Haptics Rendering
Pipeline (1/2)

• Collision detection stage
• Load the physical characteristics of the 3D
  objects from the database
• Perform collision detection to determine which
  virtual objects collide
• Force computation stage
• Compute the collision forces
• Force smoothing
• Force mapping

16
The stages of the Haptics Rendering
Pipeline (2/2)

• Tactile computation stage
• Render the touch feedback component of the
  simulation
• The computed effects are added to the force
  vector send to the haptics output display
• The haptics rendering pipeline has a much less
  standardized architecture compared to its
  graphics counterpart.

17

• Thank you

18
Conceptual Model of VR
Human
H-sensor perception cognition motion
control H-effector
V-sensor
P-effector
L-effector
virtual object
sensing
avatar
action
V-effector
L-sensor
P-sensor
Logical devices for displacements, angles, events.
19
Functional model
rendering (chap. 7)
displaying (Sec. 3-4,5,6,7)
simulation (Sec. 6-3,4)
VW DB (Sec. 6-1)
Virtual perception (chap. 4)
Interaction (chap. 5)
Sensing (Sec. 3-3)
VW Authoring (Sec. 6-2)