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Lighting Jeff Chastine 1 Lighting Jeff Chastine 1

Lighting Jeff Chastine 1 - PowerPoint Presentation

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Lighting Jeff Chastine 1 - PPT Presentation

What is Light A very complex process Find a dark area how is it being lit Light bounces mirrors shiny objects Light refracts through other media water heat Light comes from everywhere Global Illumination ID: 697583

jeff light directional chastine light jeff chastine directional lighting specular color diffuse lights object basic emit final triangle determine global ambient components

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Slide1

Lighting

Jeff Chastine

1Slide2

What is Light?

A very complex process

Find a dark area – how is it being lit?

Light bounces (mirrors, shiny objects)

Light refracts through other media (water, heat)Light comes from everywhere (Global Illumination)Light bounces off of lakes in weird ways (Fresnel effect)THUSWe’re forced to make approximationsTradeoff between time and realism“If it looks good, it is good” – Michael Abrash

http://darrentakenaga.com/3d.html

http://en.wikipedia.org/wiki/File:Global_illumination.JPG

Jeff ChastineSlide3

Two components

Light Source Properties

Color (Wavelength(s) of light)

Shape

DirectionObject PropertiesMaterialGeometryAbsorptionSlide4

4

Global Effects

translucent surface

shadow

multiple reflectionSlide5

A Basic Lighting Concept

How can we determine how much light should be cast onto a triangle from a directional light?

P

2

P

0

P

1

Directional light

- position doesn’t matter

- triangle is almost fully lit

 

Jeff Chastine

5Slide6

A Basic Lighting Concept

How can we determine how much light should be cast onto a triangle from a directional light?

P

2

P

0

P

1

(Triangle less lit)

 

Jeff Chastine

6Slide7

A Basic Lighting Concept

How can we determine how much light should be cast onto a triangle from a directional light?

P

2

P

0

P

1

(Little to no light hits the surface)

 

Jeff Chastine

7Slide8

A Basic Lighting Concept

How can we determine how much light should be cast onto a triangle from a directional light?

P

2

P

0

P

1

(Directional light)

 

Jeff Chastine

8Slide9

A Basic Lighting Concept

How can we determine how much light should be cast onto a triangle from a directional light?

P

2

P

0

P

1

(Directional light)

 

 

Jeff Chastine

9Slide10

A Basic Lighting Concept

How can we determine how much light should be cast onto a triangle from a directional light?

P

2

P

0

P

1

(Directional light)

 

 

Lesson learned: Lighting depends on angles between vectors!

Jeff Chastine

10Slide11

A Basic Lighting Concept

How can we determine how much light should be cast onto a triangle from a directional light?

P

2

P

0

P

1

(Directional light)

 

 

 

Assuming

N

and

L

are normalized, and

N∙L

isn’t negative

Jeff Chastine

11Slide12

Basic Lighting

Four independent components:

Diffuse

– the way light “falls off” of an object

Specular – the “shininess” of the objectAmbient – a minimum amount of light used to simulate “global illumination”Emit – a “glowing” effect

Only diffuse

Jeff Chastine

12Slide13

Basic Lighting

Four independent components:

Diffuse – the way light “falls off” of an object

Specular

– the “shininess” of the objectAmbient – a minimum amount of light used to simulate “global illumination”Emit – a “glowing” effect

Diffuse+Specular

Jeff Chastine

13Slide14

Basic Lighting

Four independent components:

Diffuse – the way light “falls off” of an object

Specular – the “shininess” of the object

Ambient – a minimum amount of light used to simulate “global illumination”Emit – a “glowing” effect

Ambient

Diffuse+Specular+Ambient

Jeff Chastine

14Slide15

Basic Lighting

Four independent components:

Diffuse – the way light “falls off” of an object

Specular – the “shininess” of the object

Ambient – a minimum amount of light used to simulate “global illumination”Emit – a “glowing” effect

D+S+A+Emit

Note: emit does not produce light!

Jeff Chastine

15Slide16

Interaction between Material and Lights

Final color of an object is comprised of many things:

The base object color (called a “material”)

The light color

Example: a purple light on a white surfaceAny textures we apply (later)Materials and lights have four individual componentsDiffuse color (cd and

ld) Specular color (cs and l

s) Ambient color (

ca and la) Emit color (

ce and

l

e

)

c

d

*

l

d

= [cd.r*ld.r

, cd.g

*ld.g , cd.b*ld.b] // R, G, BJeff Chastine16Slide17

Light Source Direction

In computer graphics, we usually treat lights as

rays

emanating from a source. The

direction

of these rays can either be:

Omni-directional (point light source)

Directional angle (spotlights)

Directional (parallel rays)Slide18

General Lighting

Primary vectors

l

– the incoming light vector

n – the normal of the plane/vertexr – the reflection vectorv – the viewpoint (camera)

l

n

r

θ

θ

v

Jeff Chastine

18Slide19

Diffuse Term

Contribution that a light has on the surface,

regardless of viewing direction

.

A ray of light coming in has an equal chance of being reflected in any direction.What are some ideal diffuse surfaces?Slide20

Lambertian

ReFlectance(diffuse Component)

Light falling on an object is the same

regardless

of the observer’s viewpointGood for rough surfaces without specular highlights

where

and

are normalized 

l

n

θ

Jeff Chastine

20Slide21

Lambertian

ReFlectance(diffuse Component)

Light falling on an object is the same

regardless

of the observer’s viewpointGood for rough surfaces without specular highlights

where

and

are normalized 

l

n

θ

Note:

final_color

diffuse

has R, G, B

scalar

3 parts (R, G, B)

Jeff Chastine

21Slide22

Lambertian

ReFlectance(diffuse Component)

Technically, it should be:

 

l

n

θ

Jeff Chastine

22Slide23

BLINN-PHONG Reflection

(Specular Component)

Describes the specular highlight and is

dependent on viewpoint

vAlso describes a “half-vector” h that is halfway between v and l

l

n

r

θ

θ

v

h

Jeff Chastine

23Slide24

BLINN-PHONG Reflection

(Specular Component)

-

which is really

Blinn’s contribution to the original Phong model

 

l

n

r

θ

θ

v

h

Note: vectors should be normalized

Jeff Chastine

24Slide25

BLINN-PHONG Reflection

(Specular Component)

Our final specular equation is:

 

l

n

r

θ

θ

v

h

Jeff Chastine

25Slide26

Determining

 

Realize that

will always be < 1.0, so raising it to a power will make it smaller

is the “shininess” factor

It relates to the size of the specular highlight

 

s

= ~1

s

= ~30

s

= ~255

Jeff Chastine

26

 Slide27

Ambient and Emit Components

Ambient:

Used to simulate light bouncing around the environment (global illumination)

Real world is far too complex for real

time, so just add a little light!Emit:Used to make the object “glow”Does not emit light!!!Both:Independent of viewpointSuper easy to calculate

 

Jeff Chastine

27Slide28

Final Color

To determine the final color (excluding textures) we sum up all components:

http://en.wikipedia.org/wiki/Phong_reflection_model

final_color

diffuse

final_color

specular

final_colorambientfinal_color

emit

final_color

+

Jeff Chastine

28Slide29

What about Multiple lights?

Calculate final colors and sum them all together

Assuming results are in

f

[ ] and there are count number of lights

 

Jeff Chastine

29Slide30

Common Kinds of Lights

Point light

Directional Light

Spot Light

Area LightInteresting fact:Lights cannot be seen!Only their effectsWe can light per vertex (fast) or per fragment (slower)Jeff Chastine30Slide31

Point Lights

These lights have a position in 3D space

Sometimes called a “Lamp”

Light emanates from the light in all directions

Distance

d determines brightness (“attenuation”):

 

Here, per

fragment

lighting used

Jeff Chastine

31Slide32

Point Lights

These lights have a position in 3D space

Sometimes called a “Lamp”

Light emanates from the light in all directions

Distance

d determines brightness (“attenuation”):

 

Here, per

vertex

lighting used

Jeff Chastine

32Slide33

Directional Lights

Are infinitely far away

position in NO WAY matters

Have only

directionAll objects are lit evenlySometimes called a “Sun”

Jeff Chastine

33Slide34

Spotlights

Point light source

Conical in shape

Jeff Chastine

34Slide35

Spotlights

Point light source

Conical in shape

Have:

An inner and outer cone angleUmbra – areas that are fully in shadowPenumbra – areas that are in partial shadowNote: There’s an ambient light

Jeff Chastine

35Slide36

Area Lights

A “surface” lights objects

Has a position and direction

Provides for a smoother drop off than point

Larger surface == smoother shadowsExpensive to calculate

Jeff Chastine

36Slide37

What you’ll see if you don’t

glEnable

(GL_LIGHTING)

The End!