comp 102 computer graphics and...

COMP 102Computer Graphics

and Animation

Paul Kry

4 November, 2013

“There is no reason anyone would want a computer in their home.”Ken Olson, founder and president of DEC, 1977

“640K ought to be enough for anybody.”Bill Gates, cofounder of Microsoft, 1981

“Computers are useless. They can only give you answers”

Pablo Picasso

Meats Meier

Art

Kenneth A. Huff

Movies

Visualization

NASA[Li et al., 2007]

CM Labs, crane simulator

Training

Boeing 747 flight simulator

Microsoft flight simulator

What is Computer Graphics?

• A vast field that encompasses pretty much anything related to computer generated images– Modeling, rendering, animation,

image processing, visualization, interactive techniques, etc.

[example assignments and projects from 557 and 559]

Computer Graphics

Mathematics made visible

Evolution of computing environments

• Graphics has been a key to technology growth – Graphical user interfaces– Desktop publishing – Visualization– Gaming consoles

• Hardware revolution drives everything– price/performance

improving exponentially (Moore’s Law)

– Graphics processors oneven faster exponentials

[van Dam]

Date

Price

CPU

Memory

Storage

Monitor

Devices

GUI

1984 2012

$2500 $2000

8 MHz 3.1 GHz (Quad)

128KB RAM 4.0GB DDR2 SDRAM

(1 GB on GPU)

400KB Floppy 1TB Hard Disk

9” Black&White 27” Color512 x 342

68 dpi2560 x 1440

108 dpi

MouseKeyboard

MouseKeyboard

Desktop WIMP Desktop WIMP

+28

x .8

x 387(x 1550)

x 31250

x 2500000

x 3

x 21

x 1.6

samesame

same

Original Macintosh New iMac 27”

[van Dam]

Graphics Processing Unit (GPU)Not part of the previous comparison

GPUs now part of every machine,

arguably more powerful than CPUs

and programmable

2012

4,000,000,00010-Core Xeon

GTX680

Outline

• Geometry representation

• Rendering techniques

• Animation introduction

Representing Geometry

• Parametric / Explicit

– Points

– Line segments (2 points)p(t) = a t + b (1-t) t=[0,1]

– Triangles (3 points)

– Quadrilaterals (4 points)

– Parametric surfaces(x,y,z) = f(u,v)

• Implicit

– Geometry defined by the 3D points that satisfy

F(x,y,z) = 0

– Example: a planeF(x,y,z) = ax + by + cz + d

– Example: a sphereF(x,y,z) = x2 + y2 + z2 - 1

b

a

What is the best representation?

Where does geometry come from?


Artists

CAD models

[ES3DStudios][Mudbox]


Measurement• Multi camera stereo

• Laser scans

• Medical scans

[Beeler et al 2010]

Where does geometry come from?Procedural• Noise

• Fractals

• L-systems

• Scripts


Physically Based Modeling• Shapes produced through physics simulation

[Thürey et al. 2010] [Bridson et al. 2002]

Drawing Geometry

• Object Order Rendering

– Uses points, lines, and triangles(other geometry is converted to these primitives)

– Points defining primitives are projected onto the viewing plane, and rasterized (filled in)

• Image Order Rendering

– Called ray tracing (or ray casting) as a ray is generated for each pixel in the image

– Find intersections between rays and scene geometry

Object Order Rendering• Points, lines, and triangles

– All are defined by points

[Durand]

Object Order Rendering

Points are projected onto the image plane (left)

Triangle is rasterized (right)

[Durand]

Rasterization / Scan Conversion

• Drawing a line– For horizontal, vertical and

diagonal lines all pixels lie on ideal line

– For lines at arbitrary angle, pick pixels closest to ideal line

– Aliasing “Jaggies” fixed by adjusting intensity

Visibility • Painter’s algorithm

– Sort back to front

– Draw!

– Doesn’t always work...

[Durand]

Visibility • Binary space partition

– Linear time back to front sort

– Key to 3D games before consumer level GPUs (Doom 1993)

– Still important in modern games for culling geometry

[Durand]

Visibility • Z-buffer

– Store depth at every pixel

– Compare when rasterizing

Texture Mapping

Lighting / Shading

• How much light reflected to the eye?

• Depends on angles, materials

• What if light is occluded?

Object Order Rendering Summary

• FAST! Used for most interactive applications

• Also used for most movie production (e.g., Renderman used for Pixar films)

• Consumer graphics cards can render millions of triangles per frame

• Tricky to render realistic light transport (soft shadows, glossy reflections)

Image Order Rendering

• Follow light path in reverse, back toward the light

– Ray tracing finds the intersection of scene geometry with a ray starting at the eye and going through each pixel of the image plane.

Ray Tracing

• Cast rays from viewpoint through each pixel

• Lots of rays to cast... Expensive!

[Durand]

Ray Tracing

• Deal with shadows by casting more rays

– Cast rays from visible point towards lights

[Durand]

Reflection and Refraction

Relatively easy, just cast more rays

NV

IDIA

Op

tix

Motion Blur


Co

ok e

t a

l. 1

98

4 (

Lu

ca

sfilm

)

Depth of Field


Lu

is A

lma

za

n(V

-Ra

y)

Lighting / Shading

• The full problem is actually much more complex!!!

– Light is everywhere and can even be scattered beneath the surface of materials

– Global illumination (holy grail of rendering)

[spin99, GELATO]

Ray Tracing Global Illumination• Even more rays to cast!

Super Expensive!

• Possible through careful sampling (e.g., Monte Carlo methods) and path tracing (working both from lights and viewer)[Durand]

“If you were plowing a field, which would you rather use: Two strong oxen or 1024 chickens?”

Seymour Cray

• NVIDIA GTX680 (2012)

• 3.5 billion transistors

• 1536 unified shaders

• IBM Cell processor

• PS3 (2005)

• 1 PPE + 8 SPE

Real time ray tracing

• 2007 - IBM

300000 triangles, 60 fps, 1080p, 14 Cell processors (PS3)http://www.youtube.com/watch?v=zKqZKXwop5E

• Today – NVIDIA

OPTIX / CUDA

2496 processors in TESLA K20

Design Garage Demo (2010)http://www.youtube.com/watch?v=kcP1NzB49zU

Image Order Rendering Summary

• Typically slower but easily parallelizable

• Smart data structures necessary to speed up ray scene intersections

• Easy to generate a variety of light transport effects, such as reflections on smooth surfaces

• Sampling provides a straightforward approach to many rendering issues

– depth of field, motion blur, area lights, BRDFs, antialiasing, etc.

2D Images of 3D scenes

• The goal of rendering is typically to create images that provide information about a 3D world, much in the same way a camera can be used to take a picture

– Why does this work?

– What influences our perception of depth?

reflection

stereopsisdefocus

fog / atmospheric

shading

texture gradient

occlusion

vergenceaccommodation

shadows

perspective size familiarityheight in image

Computer Animation

Where does motion come from?

• Artist based

– Key frames

• Physically based

– Simulation / Control

• Phenomenological

– Procedural animation

• Reality based

– Motion capture

Artists / Animators

Key frames

Artists / Animators

Inverse kinematics [Nakamura]

Blend Shapes

Physically based simulation

Physically based simulation

[Fedkiw et al.]

Procedural Animation

• Flocking behaviour and crowds

Boids [Reynolds 1987] Aggregate Dynamics [Narain et al. 2009]

Procedural Animation

Curl noise for procedural fluid flow, Bridson

Motion Capture

• Directly captures subtleties of human motion

Motion Capture

Andy SerkisGollum

Motion Capture

Brian Carpenter

Motion Capture

[Softimage Facerobot]

Motion Capture

[Park, Hodgins, 2006]

Where does motion come from?

• Artist based– Key frames, blend shapes, inverse kinematics,

other tools

• Physically based– Simulation of equations of motion,

– Simulation of motor control

• Phenomenological– Procedural animation

• Reality based – Motion capture

Time Permitting

A quick introduction to physically based animation

Physically Based Computer Animation

• Differences from engineering and physics– Computer animation

• High visual detail

• High performance

• Low memory consumption

– Engineering and Numerical Physics

• Momentary visual details not needed

• Predict long term behaviour and or high precision

• High computation time and memory consumption

It Came From Beneath The Sea (1955)“Fed up with traffic noise, Ray Harryhausen's giant six-tentacledoctopoid (cut back from eight to reduce stop-motion animation time),demolishes the Golden Gate Bridge.”

Motivation for physically based animation

• Physics in games?

– Add reality things move as you would expect

– Add variety different things happen

– Add fun

• Secondary animation

• Physics in training simulations?

• Physics in special effects?

• Why not? Hard?

Physically Based Animation

M x = f(x,x).. .

x(t)

Example forces:

gravity, f = m g

wind / drag, f = b x

springs, f = k x

user interaction, etc...

.

hard to compute exactly

x(0)

Discrete time steps

M x = f(x,x).. .

x(t) hard to compute exactly

x(0)

Discrete time steps

M x = f(x,x).. .

x0 = x(0)

x1 = x(h)

x2 = x(2h)

x(t) hard to compute exactly

Discrete time steps

M x = f(x,x).. .

x0

x1

x2

Numerical IntegrationForward Euler

x1 = x0 + h x0

..x = M-1 f(x,x).. . .

x0

x1

x2

.

Numerical IntegrationForward Euler

.x1 = x0 + h x0

x = M-1 f(x,x).. .

M-1 f(x0,x0).

x1 = x0 + h.

x0

x1

x2

.

Numerical IntegrationSymplectic Euler

.x1 = x0 + h x1

M-1 f(x0,x0).

x1 = x0 + h.

x0

x1

x2

.

Numerical IntegrationBackwards Euler

.x1 = x0 + h x1

M-1 f(x1,x1).

x1 = x0 + h.

x0

x1

x2

.

comp 102 computer graphics and...

Documents