JEFF CHASTINE 1

LIGHTING

JEFF CHASTINE

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)

• THUS

• We’re forced to make approximations

• Tradeoff 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 CHASTINE 3

A BASIC LIGHTING CONCEPT• How can we determine how much light should be cast onto a triangle from a directional

light?

P2

P0

P1

Directional light - position doesn’t matter- triangle is almost fully lit

𝑁

JEFF CHASTINE 4

A BASIC LIGHTING CONCEPT• How can we determine how much light should be cast onto a triangle from a directional

light?

P2

P0

P1

(Triangle less lit)𝑁

JEFF CHASTINE 5

A BASIC LIGHTING CONCEPT• How can we determine how much light should be cast onto a triangle from a directional

light?

P2

P0

P1

(Little to no light hits the surface)

𝑁

JEFF CHASTINE 6

A BASIC LIGHTING CONCEPT• How can we determine how much light should be cast onto a triangle from a directional

light?

P2

P0

P1

(Directional light)𝑁

JEFF CHASTINE 7

A BASIC LIGHTING CONCEPT• How can we determine how much light should be cast onto a triangle from a directional

light?

P2

P0

P1

(Directional light)𝑁

𝐿

JEFF CHASTINE 8

A BASIC LIGHTING CONCEPT• How can we determine how much light should be cast onto a triangle from a directional

light?

P2

P0

P1

(Directional light)𝑁

𝐿

Lesson learned: Lighting depends on angles between vectors!

JEFF CHASTINE 9

A BASIC LIGHTING CONCEPT• How can we determine how much light should be cast onto a triangle from a directional

light?

P2

P0

P1

(Directional light)𝑁

𝐿

intensity=acos (𝑁 ∙𝐿)

Assuming N and L are normalized, and N∙L isn’t negative

JEFF CHASTINE 10

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

Only diffuse

JEFF CHASTINE 11

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

Diffuse+Specular

JEFF CHASTINE 12

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 13

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 14

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 surface

• Any textures we apply (later)

• Materials and lights have four individual components

• Diffuse color (cd and ld)

• Specular color (cs and ls)

• Ambient color (ca and la)

• Emit color (ce and le)

• cd * ld=[cd.r*ld.r,cd.g*ld.g,cd.b*ld.b] // R, G, B

JEFF CHASTINE 15

GENERAL LIGHTING• Primary vectors

• l – the incoming light vector

• n – the normal of the plane/vertex

• r – the reflection vector

• v – the viewpoint (camera)

l n

r

θ θ

v

JEFF CHASTINE 16

LAMBERTIAN REFLECTANCE(DIFFUSE COMPONENT)

• Light falling on an object is the same regardless of the observer’s viewpoint

• Good for rough surfaces without specular highlights

• where and are normalized

l n

θ

JEFF CHASTINE 17

LAMBERTIAN REFLECTANCE(DIFFUSE COMPONENT)

• Light falling on an object is the same regardless of the observer’s viewpoint

• Good for rough surfaces without specular highlights

• where and are normalized

l n

θ

Note: final_colordiffuse has R, G, B

scalar 3 parts (R, G, B)

JEFF CHASTINE 18

LAMBERTIAN REFLECTANCE(DIFFUSE COMPONENT)

• Technically, it should be:

l n

θ

JEFF CHASTINE 19

BLINN-PHONG REFLECTION(SPECULAR COMPONENT)

• Describes the specular highlight and is dependent on viewpoint v

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

l

n

r

θ θ

v

h

JEFF CHASTINE 20

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 21

BLINN-PHONG REFLECTION(SPECULAR COMPONENT)

• Our final specular equation is:

l

n

r

θ θ

v

h

JEFF CHASTINE 22

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

𝑓𝑖𝑛𝑎𝑙𝑐𝑜𝑙𝑜𝑟 𝑠=(𝑛 ∙ h)𝑠∗𝑐𝑠∗𝑙𝑠

JEFF CHASTINE 23

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 viewpoint

• Super easy to calculate

JEFF CHASTINE 24

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

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

final_colordiffusefinal_colorspecularfinal_colorambientfinal_coloremit

final_color

+

JEFF CHASTINE 25

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 26

COMMON KINDS OF LIGHTS• Point light

• Directional Light

• Spot Light

• Area Light

• Interesting fact:

• Lights cannot be seen!

• Only their effects

• We can light per vertex (fast) or per fragment (slower)

JEFF CHASTINE 27

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 28

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 29

DIRECTIONAL LIGHTS• Are infinitely far away

• position in NO WAY matters

• Have only direction

• All objects are lit evenly

• Sometimes called a “Sun”

JEFF CHASTINE 30

SPOTLIGHTS• Point light source

• Conical in shape

JEFF CHASTINE 31

SPOTLIGHTS• Point light source

• Conical in shape

• Have:

• An inner and outer cone angle

• Umbra – areas that are fully in shadow

• Penumbra – areas that are in partial shadow

• Note: There’s an ambient light

JEFF CHASTINE 32

AREA LIGHTS• A “surface” lights objects

• Has a position and direction

• Provides for a smoother drop off than point

• Larger surface == smoother shadows

• Expensive to calculate

What you’ll see if you don’t glEnable(GL_LIGHTING)

THE END!