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Radiosity Ray Tracing and Radiosity Ray Tracing and Radiosity Form Factors Form Factors Enhancements Enhancements Two-pass Rendering Two-pass Rendering Thursday, April 1, 2010 Outline Outline A Brief Review/Introduction to Radiosity

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SLIDE 1

Radiosity

Ray Tracing and Radiosity Form Factors Enhancements Two-pass Rendering Ray Tracing and Radiosity Form Factors Enhancements Two-pass Rendering

Thursday, April 1, 2010

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SLIDE 2

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 3 3

Outline Outline

  • A Brief Review/Introduction to Radiosity

A Brief Review/Introduction to Radiosity

  • The Radiosity Equation, Form Factors

The Radiosity Equation, Form Factors

  • Putting it all together, and Improving

Putting it all together, and Improving

  • More Realism: A digression, and Two

More Realism: A digression, and Two-

  • Pass

Pass Rendering Rendering

Thursday, April 1, 2010

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SLIDE 3

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 4 4

Review: Local vs. Global Illumination Review: Local vs. Global Illumination Local illumination: Local illumination: Phong Phong model model (OpenGL, most real (OpenGL, most real-

  • time graphics)

time graphics)

– – Light to single surface point to viewer Light to single surface point to viewer – – FAST FAST – – Vastly simplified Vastly simplified – – No representation of many natural No representation of many natural phenomena (shadows, inter phenomena (shadows, inter-

  • reflections)

reflections) without additional hacks without additional hacks

Local Illumination

  • fast
  • simple
  • light → surface → viewer
  • ignores many important

effects

Thursday, April 1, 2010

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SLIDE 4

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 5 5

Review: Local vs. Global Illumination Review: Local vs. Global Illumination

  • Global illumination:

Global illumination: Ray tracing Ray tracing

– – Realistic specular reflection/transmission Realistic specular reflection/transmission – – Simplified diffuse reflection* Simplified diffuse reflection*

  • Global illumination:

Global illumination: Radiosity Radiosity

– – Realistic diffuse reflection Realistic diffuse reflection – – Diffuse Diffuse-

  • only: No specular interaction*
  • nly: No specular interaction*

indirect direct both

Thursday, April 1, 2010

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SLIDE 5

6 Computer Graphics 15-462

Beyond Ray Tracing

Ray tracing ignores the diffuse component of incident illumination

–to achieve this component requires sending out rays from each surface point for the whole visible hemisphere

Even if you could compute such a massive problem there is a conceptual problem—loops:

–point A gets light from point B –point B also gets light from point A

Thursday, April 1, 2010

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SLIDE 6

7 Computer Graphics 15-462

Doing it Right The real solution is to solve simultaneously for incoming and outgoing light at all surface points

this is a massive integral equation

Radiosity deals with the relatively easy case of purely diffuse scenes Or, you can sample many, many complete paths from light source to camera (photon mapping)

Thursday, April 1, 2010

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SLIDE 7

Key Idea

  • Model diffuse interaction only!

incoming light

  • utgoing light

Thursday, April 1, 2010

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SLIDE 8

7 Computer Graphics 15-462

Doing it Right The real solution is to solve simultaneously for incoming and outgoing light at all surface points

this is a massive integral equation

Radiosity deals with the relatively easy case of purely diffuse scenes Or, you can sample many, many complete paths from light source to camera (photon mapping)

Thursday, April 1, 2010

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SLIDE 9

7 Computer Graphics 15-462

Doing it Right The real solution is to solve simultaneously for incoming and outgoing light at all surface points

this is a massive integral equation

Radiosity deals with the relatively easy case of purely diffuse scenes Or, you can sample many, many complete paths from light source to camera (photon mapping)

Thursday, April 1, 2010

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SLIDE 10

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 8 8

Advantages to diffuse Advantages to diffuse-

  • only model?
  • nly model?

Specular interaction depends on viewer position Specular interaction depends on viewer position— — diffuse does not diffuse does not Result: The color seen at any point on any visible Result: The color seen at any point on any visible surface is independent of viewer position surface is independent of viewer position Radiosity produces a 3D model of surface patches Radiosity produces a 3D model of surface patches with colors assigned to each with colors assigned to each Can be rendered in OpenGL Can be rendered in OpenGL Useful for Useful for architectual architectual fly fly-

  • throughs

throughs. .

Thursday, April 1, 2010

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SLIDE 11

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 5 5

Review: Local vs. Global Illumination Review: Local vs. Global Illumination

  • Global illumination:

Global illumination: Ray tracing Ray tracing

– – Realistic specular reflection/transmission Realistic specular reflection/transmission – – Simplified diffuse reflection* Simplified diffuse reflection*

  • Global illumination:

Global illumination: Radiosity Radiosity

– – Realistic diffuse reflection Realistic diffuse reflection – – Diffuse Diffuse-

  • only: No specular interaction*
  • nly: No specular interaction*

indirect direct both

Thursday, April 1, 2010

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SLIDE 12

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 5 5

Review: Local vs. Global Illumination Review: Local vs. Global Illumination

  • Global illumination:

Global illumination: Ray tracing Ray tracing

– – Realistic specular reflection/transmission Realistic specular reflection/transmission – – Simplified diffuse reflection* Simplified diffuse reflection*

  • Global illumination:

Global illumination: Radiosity Radiosity

– – Realistic diffuse reflection Realistic diffuse reflection – – Diffuse Diffuse-

  • only: No specular interaction*
  • nly: No specular interaction*

indirect direct both

Thursday, April 1, 2010

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SLIDE 13

11 Computer Graphics 15-462

Radiosity Examples

http://www.autodesk.com/us/lightscape/examples/html/index.htm

Thursday, April 1, 2010

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SLIDE 14

12 Computer Graphics 15-462

Raytracing Examples

http://www.povray.org/

Thursday, April 1, 2010

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SLIDE 15

18 Computer Graphics 15-462

Raytracing Examples

http://www.povray.org/

Thursday, April 1, 2010

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SLIDE 16

19 Computer Graphics 15-462

Radiosity Examples

http://www.autodesk.com/us/lightscape/examples/html/index.htm

Thursday, April 1, 2010

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SLIDE 17

11 Computer Graphics 15-462

Radiosity Examples

http://www.autodesk.com/us/lightscape/examples/html/index.htm

Radiosity Raytracing

Thursday, April 1, 2010

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SLIDE 18

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 24 24

Outline Outline

  • A Brief Review/Introduction to Radiosity

A Brief Review/Introduction to Radiosity

  • The Radiosity Equation, Form Factors

The Radiosity Equation, Form Factors

  • Putting it all together, and Improving

Putting it all together, and Improving

  • More Realism:

More Realism: A digression, and Two

A digression, and Two-

  • Pass Rendering

Pass Rendering

Thursday, April 1, 2010

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SLIDE 19

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 5 5

Review: Local vs. Global Illumination Review: Local vs. Global Illumination

  • Global illumination:

Global illumination: Ray tracing Ray tracing

– – Realistic specular reflection/transmission Realistic specular reflection/transmission – – Simplified diffuse reflection* Simplified diffuse reflection*

  • Global illumination:

Global illumination: Radiosity Radiosity

– – Realistic diffuse reflection Realistic diffuse reflection – – Diffuse Diffuse-

  • only: No specular interaction*
  • nly: No specular interaction*

indirect direct both

Thursday, April 1, 2010

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SLIDE 20

Far Too Many Points

{ {

Patch

{

Patch

{

Patch

{

Patch

  • Concentrate on patches instead.
  • Want to have as few as possible.

Thursday, April 1, 2010

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SLIDE 21

9 Computer Graphics 15-462

Radiosity

Simple scene with diffuse surfaces White wall should show effect of being near red wall Compute light reflected between each pair of patches

Red Patch White Patch

Thursday, April 1, 2010

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SLIDE 22

9 Computer Graphics 15-462

Radiosity

Simple scene with diffuse surfaces White wall should show effect of being near red wall Compute light reflected between each pair of patches

Thursday, April 1, 2010

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SLIDE 23

10 Computer Graphics 15-462

Radiosity

Closed environment (office, factory) Compute interaction between all patches (over which intensity is assumed to be constant) View independent Difficult to do specular highlights

Thursday, April 1, 2010

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SLIDE 24

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 21 21

Classical Radiosity in a Nutshell Classical Radiosity in a Nutshell

Divide all surfaces into patches (squares are Divide all surfaces into patches (squares are typical). typical). Determine a set of linear equations to model Determine a set of linear equations to model inter inter-

  • reflection between all patches.

reflection between all patches. Solve set of simultaneous equations. Solve set of simultaneous equations. Render using standard hardware. Render using standard hardware.

Thursday, April 1, 2010

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SLIDE 25

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 22 22

Assumptions of Classical Radiosity Assumptions of Classical Radiosity

No participating media (no light interaction No participating media (no light interaction with air, fog, etc) with air, fog, etc) Opaque surfaces Opaque surfaces— —no transmission no transmission Radiosity Radiosity is constant across element is constant across element Colors (R, G, B) are independent Colors (R, G, B) are independent

Thursday, April 1, 2010

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SLIDE 26

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 23 23

Assumptions of Classical Radiosity Assumptions of Classical Radiosity

Diffuse Diffuse-

  • only reflection and emission, so
  • nly reflection and emission, so
  • utgoing light radiates equally in all
  • utgoing light radiates equally in all

directions directions Light radiating from a point on a surface is Light radiating from a point on a surface is independent of position on the surface independent of position on the surface— — constant constant “ “radiosity radiosity” ” across a single surface across a single surface

Thursday, April 1, 2010

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SLIDE 27

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 25 25

What What is is radiosity? radiosity?

  • Radiosity B(x) = dP/dA

– P => Energy (light “intensity”) – A => Area

  • Integrating radiosity over a patch with

respect to A will yield P for the patch

  • Thus, radiosity is a representation of a

patch’s intensity of light per unit area

Thursday, April 1, 2010

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SLIDE 28

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 26 26

What What is is radiosity? radiosity?

  • Radiosity determined by the sum of the emitted

Radiosity determined by the sum of the emitted and reflected energy: and reflected energy:

  • i

i identifies the patch whose radiosity is being identifies the patch whose radiosity is being determined determined j j identifies a single other patch identifies a single other patch E E is emitted energy (light sources) is emitted energy (light sources) R R is reflectance (how much incoming light is is reflectance (how much incoming light is reflected) reflected) F F is the form factor between two patches is the form factor between two patches

!

" #

j ji j j i i i i i

F A B R A E A B

Thursday, April 1, 2010

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SLIDE 29

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 27 27

What What is is radiosity? radiosity?

  • Radiosity determined by the sum of the emitted

Radiosity determined by the sum of the emitted and reflected energy: and reflected energy:

  • Outgoing energy =

Outgoing energy = Emitted energy + Reflected energy Emitted energy + Reflected energy

!

" #

j ji j j i i i i i

F A B R A E A B

Thursday, April 1, 2010

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SLIDE 30

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 28 28

Form Factor? Form Factor?

  • F

Fij

ij:

: Fraction of light leaving patch Fraction of light leaving patch i i arriving arriving at patch at patch j j

  • Determined by properties of

Determined by properties of i i and and j j: :

– – Shape Shape – – Distance Distance – – Orientation Orientation – – Occlusion by other patches Occlusion by other patches

Thursday, April 1, 2010

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SLIDE 31

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 29 29

Form Factor Equation Form Factor Equation

x x and and y y are points in are points in i i and and j j respectively respectively r r is distance from is distance from x x to to y y Thetas are angles between patch normals and line Thetas are angles between patch normals and line between between x x and and y y v v( (x x, ,y y) is a visibility function ) is a visibility function Can points Can points x x and and y y see each other? see each other?

! !

" "

#

i j

P x P y ij i

dydx y x v r F A ) , ( * ' cos cos

2

$ % %

Thursday, April 1, 2010

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SLIDE 32

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 30 30

Simplify Simplify

Form factors are symmetric: Form factors are symmetric: Divide radiosity equation by Divide radiosity equation by A Ai

i

ji j ij i

F A F A !

"

# !

j ji j j i i i i i

F A B R A E A B

" "

# ! # !

j ij j i i i j i ji j j i i i

F B R E B A F A B R E B /

Thursday, April 1, 2010

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SLIDE 33

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 31 31

Linear System Linear System

Our new equation gives the radiosity ( Our new equation gives the radiosity (B B) of a ) of a single patch, so to specify the radiosity of all single patch, so to specify the radiosity of all n n patches we need patches we need n n radiosity equations, one for radiosity equations, one for each patch each patch Known values: Known values: E E (given), (given), R R (given), (given), F F (computable) (computable) Unknown: Unknown: B B n n equations, equations, n n unknowns unknowns

!

" #

j ij j i i i

F B R E B

Thursday, April 1, 2010

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SLIDE 34

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 32 32

Linear System Linear System

Restate as a matrix equation Restate as a matrix equation… …and solve and solve Each of our Each of our n n linear equations contains linear equations contains n n double integrals, one for each form factor. double integrals, one for each form factor.

! ! ! ! " # $ $ $ $ % & ' ! ! ! ! " # $ $ $ $ % & ! ! ! ! " # $ $ $ $ % & ( ( ( ( ( (

n n nn n n n n n n n

E E E B B B F R F R F R F R F R F R F R F R F R ... ... * 1 ... ... ... ... ... ... 1 ... 1

2 1 2 1 2 1 2 2 22 2 21 2 1 1 12 1 11 1

Thursday, April 1, 2010

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SLIDE 35

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 33 33

The Radiosity The Radiosity “ “Pipeline Pipeline” ”

Input Scene Geometry Meshing (division into patches)

Form Factor Calculations

Input Reflectance/Emission Factors

Solve Radiosity Equation

Input Viewing Conditions

Rendering/Visualization Output Image

Texture Geometry with Radiosity Solution

Thursday, April 1, 2010

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SLIDE 36

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 34 34

Being Smart about Form Factors Being Smart about Form Factors

Form factors depend only on scene Form factors depend only on scene

  • geometry. If geometry is constant, they
  • geometry. If geometry is constant, they
  • nly need to be calculated once.
  • nly need to be calculated once.

Solution of the radiosity system is Solution of the radiosity system is independent of viewing conditions, so if independent of viewing conditions, so if

  • nly the viewer position changes, it only
  • nly the viewer position changes, it only

needs to be solved once needs to be solved once— —can walk can walk around the scene in real around the scene in real-

  • time after it

time after it’ ’s s initially generated initially generated

Thursday, April 1, 2010

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SLIDE 37

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 35 35

Being Smart about Form Factors Being Smart about Form Factors

Form factors are complicated. Full numeric Form factors are complicated. Full numeric approximation of these is expensive approximation of these is expensive— —many many special cases may be solved analytically. special cases may be solved analytically. Because we assume that radiosity is constant Because we assume that radiosity is constant across a patch, two patches are typically across a patch, two patches are typically assumed to be fully inter assumed to be fully inter-

  • visible or not at all

visible or not at all inter inter-

  • visible. That means that patches have to
  • visible. That means that patches have to

be small enough to resolve shadows and other be small enough to resolve shadows and other complexities complexities

Thursday, April 1, 2010

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SLIDE 38

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 36 36

How to perform visibility testing? How to perform visibility testing?

Two basic methods, both of which have Two basic methods, both of which have aliasing problems: aliasing problems:

Raycasting (typically slow) Raycasting (typically slow) Hemicube method (z Hemicube method (z-

  • buffer exploit)

buffer exploit)

Anti Anti-

  • aliasing may be performed in both cases

aliasing may be performed in both cases

Thursday, April 1, 2010

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SLIDE 39

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 37 37

Hemicube Visibility Testing Hemicube Visibility Testing

Render the entire scene from Render the entire scene from the perspective of the the perspective of the center of the current patch center of the current patch Rather than color, store patch Rather than color, store patch identifiers, using the z identifiers, using the z-

  • buffer to determine visibility

buffer to determine visibility Takes advantage of graphics Takes advantage of graphics hardware hardware

  • R. Ramamoorthi

Thursday, April 1, 2010

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SLIDE 40

Hemicube in Action

http://www.siggraph.org/education/materials/HyperGraph/radiosity/overview_2.htm

Thursday, April 1, 2010

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SLIDE 41

Hemicube in Action

http://en.wikipedia.org/wiki/File:Hemicube_Unfold.gif

Thursday, April 1, 2010

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SLIDE 42

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 38 38

Outline Outline

  • A Brief Review/Introduction to Radiosity

A Brief Review/Introduction to Radiosity

  • The Radiosity Equation, Form Factors

The Radiosity Equation, Form Factors

  • Putting it all together, and Improving

Putting it all together, and Improving

  • More Realism:

More Realism: A digression, and Two

A digression, and Two-

  • Pass Rendering

Pass Rendering

Thursday, April 1, 2010

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SLIDE 43

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 39 39

Classical Radiosity in a Nutshell, Classical Radiosity in a Nutshell, Revised Revised

  • Divide all surfaces into patches.

Divide all surfaces into patches.

  • Calculate form factors between all patches.

Calculate form factors between all patches.

– – Lighting and viewer independent Lighting and viewer independent

  • Solve the radiosity equation.

Solve the radiosity equation.

– – Viewer independent Viewer independent

  • Render using standard 3D hardware.

Render using standard 3D hardware.

Thursday, April 1, 2010

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SLIDE 44

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 33 33

The Radiosity The Radiosity “ “Pipeline Pipeline” ”

Input Scene Geometry Meshing (division into patches)

Form Factor Calculations

Input Reflectance/Emission Factors

Solve Radiosity Equation

Input Viewing Conditions

Rendering/Visualization Output Image

Texture Geometry with Radiosity Solution

Thursday, April 1, 2010

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SLIDE 45

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 41 41

  • F. Pfenning

Thursday, April 1, 2010

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SLIDE 46

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 42 42

Our Result Our Result

  • F. Pfenning

What is right? What is wrong?

Thursday, April 1, 2010

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SLIDE 47

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 43 43

What went right? What went right?

Inter Inter-

  • reflection effects

reflection effects— —clearly visible clearly visible between the box on the right and the wall between the box on the right and the wall

Thursday, April 1, 2010

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SLIDE 48

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 44 44

What went wrong? What went wrong?

Blocky Blocky-

  • looking

looking— —patch boundaries extremely patch boundaries extremely

  • bvious
  • bvious

Causes of blockiness Causes of blockiness

Aliasing in hemicube method causes significant Aliasing in hemicube method causes significant differences in radiosity between adjacent differences in radiosity between adjacent patches patches Large Large patch size patch size

Thursday, April 1, 2010

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SLIDE 49

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 45 45

Fixes? Fixes?

Use antialiasing to clean up hemicube Use antialiasing to clean up hemicube method method Interpolation Interpolation

Determine radiosity at each vertex of a patch Determine radiosity at each vertex of a patch and use bilinear interpolation to make things and use bilinear interpolation to make things look smoother look smoother

Increase patch resolution (decrease size) Increase patch resolution (decrease size)

Expensive if done uniformly Expensive if done uniformly – – O( O(n n2

2)

) How can we do this intelligently? How can we do this intelligently?

Thursday, April 1, 2010

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SLIDE 50

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 46 46

Antialiasing (on hemicube) Antialiasing (on hemicube)

  • F. Pfenning

Thursday, April 1, 2010

slide-51
SLIDE 51

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 47 47

Thursday, April 1, 2010

slide-52
SLIDE 52

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 48 48

Thursday, April 1, 2010

slide-53
SLIDE 53

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 49 49

Thursday, April 1, 2010

slide-54
SLIDE 54

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 50 50

Thursday, April 1, 2010

slide-55
SLIDE 55

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 51 51

Thursday, April 1, 2010

slide-56
SLIDE 56

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 52 52

Thursday, April 1, 2010

slide-57
SLIDE 57

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 53 53

Thursday, April 1, 2010

slide-58
SLIDE 58

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 54 54

Adaptive Subdivision Adaptive Subdivision

Introduce a patch substructure Introduce a patch substructure— —divide each divide each patch into smaller patch into smaller elements elements. . Keep distinction between patches and Keep distinction between patches and elements in order to avoid efficiency elements in order to avoid efficiency problems problems

Thursday, April 1, 2010

slide-59
SLIDE 59

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 55 55

Adaptive Subdivision Adaptive Subdivision

Determine light transport one Determine light transport one-

  • way from

way from patches onto elements, not analyzing , not analyzing element element-

  • to

to-

  • element interaction

element interaction O( O(mn mn) for ) for m m elements and elements and n n patches. More

  • patches. More

expensive than the original expensive than the original n n2

2 approach,

approach, since since m m >> >> n n, but much better than O( , but much better than O(m m2

2).

).

Thursday, April 1, 2010

slide-60
SLIDE 60

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 56 56

Adaptive Subdivision Adaptive Subdivision

Subdivide elements adaptively: Subdivide elements adaptively: Begin with elements identical to patches. Begin with elements identical to patches. Determine radiosity of an element, then compare to Determine radiosity of an element, then compare to neighbors to obtain an error value. If within some error neighbors to obtain an error value. If within some error threshold, assign constant radiosity (or optionally threshold, assign constant radiosity (or optionally interpolate). interpolate). Otherwise, subdivide the element and recurse until the Otherwise, subdivide the element and recurse until the error threshold or a minimum element size is reached. error threshold or a minimum element size is reached.

Thursday, April 1, 2010

slide-61
SLIDE 61

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 57 57

Adaptive Subdivision Adaptive Subdivision

Results in very smooth Results in very smooth-

  • looking results for a

looking results for a relatively small amount of extra work relatively small amount of extra work Shadows, areas near lights, and edges in Shadows, areas near lights, and edges in general look much better general look much better Not an idea specific to radiosity! Adaptive Not an idea specific to radiosity! Adaptive subdivision is a general tool used in many subdivision is a general tool used in many areas of graphics and other fields as well areas of graphics and other fields as well

Thursday, April 1, 2010

slide-62
SLIDE 62

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 58 58

Adaptive Subdivision Examples Adaptive Subdivision Examples

http://www.acm.org/jgt/papers/TeleaVanOverveld97/

Thursday, April 1, 2010

slide-63
SLIDE 63

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 59 59

http://aig.cs.man.ac.uk/gallery/vrad.html

Thursday, April 1, 2010

slide-64
SLIDE 64

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 60 60

Another example Another example

  • D. Lischinski

Thursday, April 1, 2010

slide-65
SLIDE 65

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 61 61

Outline Outline

  • A Brief Review/Introduction to Radiosity

A Brief Review/Introduction to Radiosity

  • The Radiosity Equation, Form Factors

The Radiosity Equation, Form Factors

  • Putting it all together, and Improving

Putting it all together, and Improving

  • More Realism

More Realism

Thursday, April 1, 2010

slide-66
SLIDE 66

11 Computer Graphics 15-462

Radiosity Examples

http://www.autodesk.com/us/lightscape/examples/html/index.htm

Radiosity Raytracing

Thursday, April 1, 2010

slide-67
SLIDE 67

Is raytracing really so bad?

Thursday, April 1, 2010

slide-68
SLIDE 68

14 Computer Graphics 15-462

Raytracing Examples

http://www.povray.org/

Thursday, April 1, 2010

slide-69
SLIDE 69

15 Computer Graphics 15-462

Raytracing Examples

http://www.povray.org/

Thursday, April 1, 2010

slide-70
SLIDE 70

16 Computer Graphics 15-462

Raytracing Examples

http://www.povray.org/

Thursday, April 1, 2010

slide-71
SLIDE 71

17 Computer Graphics 15-462

Raytracing Examples

http://www.povray.org/

Thursday, April 1, 2010

slide-72
SLIDE 72

Can we inject specular effects into radiosity?

Radiosity Raytracing

Thursday, April 1, 2010

slide-73
SLIDE 73

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 62 62

Yet More Realism Yet More Realism

  • D. Lischinski

Thursday, April 1, 2010

slide-74
SLIDE 74

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 63 63

Wait a minute Wait a minute… …

  • D. Lischinski

Thursday, April 1, 2010

slide-75
SLIDE 75

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 64 64

Specular Effects in Specular Effects in Radiosity Radiosity? ?

Keep viewer independence Keep viewer independence Light reflected differently in different directions Light reflected differently in different directions Calculations for each source and each Calculations for each source and each direction direction Impractical Impractical

Thursday, April 1, 2010

slide-76
SLIDE 76

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 65 65

A Better Idea: The Best of Both Worlds A Better Idea: The Best of Both Worlds

Combine radiosity and raytracing Combine radiosity and raytracing Goal: Represent four forms of light Goal: Represent four forms of light transport: transport:

– – Diffuse Diffuse -

  • > Diffuse

> Diffuse – – Diffuse Diffuse -

  • > Specular

> Specular – – Specular Specular -

  • > Diffuse

> Diffuse – – Specular Specular -

  • > Specular

> Specular

Two Two-

  • pass approach, one for each method

pass approach, one for each method

Thursday, April 1, 2010

slide-77
SLIDE 77

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 66 66

First Pass: Enhanced Radiosity First Pass: Enhanced Radiosity

Diffuse Diffuse -

  • > Diffuse

> Diffuse

Normal diffuse reflection model Normal diffuse reflection model Diffuse transmission (translucent objects) Diffuse transmission (translucent objects) – – requires requires modified form factor modified form factor

Specular Specular -

  • > Diffuse

> Diffuse

Specular transmission (transparent objects, e.g. Specular transmission (transparent objects, e.g. windows) windows) – – involves extended form factor involves extended form factor Specular reflection (reflective objects, e.g. mirrors) Specular reflection (reflective objects, e.g. mirrors) – – create actual create actual “ “mirror image mirror image” ” environment with copies environment with copies

  • f all patches. Expensive!
  • f all patches. Expensive!

Thursday, April 1, 2010

slide-78
SLIDE 78

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 67 67

Enhanced Radiosity Enhanced Radiosity -

  • Evaluation

Evaluation

  • Only accounts for a single specular

Only accounts for a single specular reflection (try creating reflection (try creating “ “mirror image mirror image” ” environments for two mirrors facing each environments for two mirrors facing each

  • ther)
  • ther)
  • Accurate diffuse model

Accurate diffuse model

  • Equations solved as in the classical

Equations solved as in the classical method method

  • Still viewer

Still viewer-

  • independent

independent

Thursday, April 1, 2010

slide-79
SLIDE 79

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 68 68

Second Pass: Enhanced Raytracing Second Pass: Enhanced Raytracing

  • Specular

Specular -

  • > Specular

> Specular

– – Reflection and transmission as in classical Reflection and transmission as in classical method method

  • Diffuse

Diffuse -

  • > Specular

> Specular

– – Use the radiosity calculated in the first pass Use the radiosity calculated in the first pass – – Integrate incoming light over a hemisphere (or Integrate incoming light over a hemisphere (or hemicube), or approximate with a tiny frustum hemicube), or approximate with a tiny frustum in the direction of reflection in the direction of reflection – – Recurse if visible surface is specular Recurse if visible surface is specular

Thursday, April 1, 2010

slide-80
SLIDE 80

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 69 69

First Pass Result First Pass Result

http://www.cg.tuwien.ac.at/research/rendering/rays-radio/

Thursday, April 1, 2010

slide-81
SLIDE 81

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 70 70

Second Pass Result Second Pass Result

(radiosity info. not yet used, just raytracing) (radiosity info. not yet used, just raytracing)

http://www.cg.tuwien.ac.at/research/rendering/rays-radio/

Thursday, April 1, 2010

slide-82
SLIDE 82

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 71 71

Combined (Final) Result Combined (Final) Result

http://www.cg.tuwien.ac.at/research/rendering/rays-radio/

Thursday, April 1, 2010

slide-83
SLIDE 83

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 72 72

Two Two-

  • Pass Global Illumination: Evaluation

Pass Global Illumination: Evaluation

Very expensive. Takes the cost of radiosity Very expensive. Takes the cost of radiosity added to the cost of raytracing and then added to the cost of raytracing and then throws even more calculations into the mix throws even more calculations into the mix Many approximations remain, particularly in Many approximations remain, particularly in specular specular -

  • > diffuse and diffuse

> diffuse and diffuse -

  • > specular

> specular transport transport

Thursday, April 1, 2010

slide-84
SLIDE 84

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 73 73

Two Two-

  • Pass Global Illumination: Evaluation

Pass Global Illumination: Evaluation

Produces very convincing effects and works Produces very convincing effects and works very well for scenes with small numbers of very well for scenes with small numbers of reflecting/transmitting objects reflecting/transmitting objects Used in combination with other methods for Used in combination with other methods for extremely high extremely high-

  • quality images

quality images

Thursday, April 1, 2010

slide-85
SLIDE 85

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 74 74

More Pretty Pictures More Pretty Pictures

  • D. Lischinski

Thursday, April 1, 2010

slide-86
SLIDE 86

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 75 75

  • D. Lischinski

Thursday, April 1, 2010

slide-87
SLIDE 87

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 76 76

Summary: Classical Radiosity Summary: Classical Radiosity

Divide all surfaces into patches. Divide all surfaces into patches. Calculate form factors between all patches. Calculate form factors between all patches.

Lighting and viewer independent Lighting and viewer independent

Solve the radiosity equation Solve the radiosity equation

Viewer independent Viewer independent

Render using standard 3D hardware. Render using standard 3D hardware.

Thursday, April 1, 2010

slide-88
SLIDE 88

15 15-

  • 462 Computer Graphics I

462 Computer Graphics I 77 77

Acknowledgements/Resources Acknowledgements/Resources

  • Demo that explores resolution and other

Demo that explores resolution and other parameters parameters

– – http://www.mvpny.com/RadTutMV/RadiosityTut1 http://www.mvpny.com/RadTutMV/RadiosityTut1 MV.html MV.html

  • T. Yeap
  • T. Yeap (many great radiosity resources)

(many great radiosity resources)

– – http:// http://www.scs.leeds.ac.uk/cuddles/rover/main.htm www.scs.leeds.ac.uk/cuddles/rover/main.htm

  • Cornell graphics group

Cornell graphics group (many pretty pictures)

(many pretty pictures) – – http:// http://www.graphics.cornell.edu www.graphics.cornell.edu/online/research /online/research/ /

Thursday, April 1, 2010