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The Rendering Pipeline

CS788 Topic of HCI 2

Outline

Introduction

The Graphics Rendering Pipeline

Three functional stages

Example

Bottleneck

Optimization

The Haptics Rendering Pipeline

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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

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The Graphics Rendering PipelineThe Graphics Rendering Pipeline

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Three functional stages

Graphics rendering has three functional stages.

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Applicationstage

Applicationstage

Geometrystage

Geometrystage

Rasterizerstage

Rasterizerstage

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tpu

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Userinput

Videocontroller

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Application stage

Implemented in software Run on several CPUs

Read the world geometry database & the user’s input

Basic operations take care of user’s input acceleration algorithm

Output: 3D geometric primitives (polygons, meshes)

Geometrystage

Geometrystage Rasterizer

stage

Rasterizerstage

Applicationstage

CPU1

CPU2

Userinput

Videocontroller

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Geometry stage

Implemented in software or hardware Run on the geometry engines

Basic operations

Output: 2D geometric primitives (2D polygons)

Applicationstage

Applicationstage Rasterizer

stage

Rasterizerstage

Geometrystage

GE1

GE2

Userinput

Videocontroller

Model transformation

Lightcomputation

Sceneprojection

ClippingScreen

mapping

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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

Applicationstage

Applicationstage Geometry

stage

Geometrystage

Rasterizerstage

RU1

RU2

Userinput

Videocontroller

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Bottleneck

One of the three stages will be the slowest => bottleneck stage

CPU-limited In the application stage

Transform-limited In the geometry stage

Fill-limited In the rasterizer stage

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Optimization (1/2)

Application stage : CPU-limited Replace the CPU with a faster one or add another CPU Reduce CPU’s 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

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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

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The Haptics Rendering PipelineThe Haptics Rendering Pipeline

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The Haptics Rendering Pipeline

Userinput

Hapticinterface

Collisiondetection stage

Force computationstage

Tactile computationstage

CPU1

CPU2

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Forc

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Forc

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ap

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gHaptic

texturing

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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

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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.

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Thank you

CS788 Topic of HCI 17

Conceptual Model of VR

H-sensor

perception

cognition

motion control

H-effector

P-effector

P-sensor

L-effector

L-sensor

sensing

action

Human

avata

r

virtu

al

agen

t

Logical devicesfordisplacements,angles,events.

virtualobject

V-effector

V-sensor

CS788 Topic of HCI 18

Functional model

displaying(Sec. 3-4,5,6,7)

rendering(chap. 7)

simulation(Sec. 6-3,4)

Interaction(chap. 5)

Virtualperception(chap. 4)

Sensing(Sec. 3-3)

VWAuthoring(Sec. 6-2)

VW DB(Sec. 6-1)