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## PowerPoint Slideshow about ' Lighting' - tarmon

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

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

Jeff Chastine

A Basic Lighting Concept

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

Directional light - position doesn’t matter

- triangle is almost fully lit

P0

P1

P2

Jeff Chastine

A Basic Lighting Concept

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

P0

(Triangle less lit)

P1

P2

Jeff Chastine

A Basic Lighting Concept

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

P0

P1

P2

(Little to no light hits the surface)

Jeff Chastine

A Basic Lighting Concept

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

P0

(Directional light)

P1

P2

Jeff Chastine

A Basic Lighting Concept

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

P0

(Directional light)

P1

P2

Jeff Chastine

A Basic Lighting Concept

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

Lesson learned: Lighting depends on angles between vectors!

P0

(Directional light)

P1

P2

Jeff Chastine

A Basic Lighting Concept

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

P0

(Directional light)

P1

P2

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

Jeff Chastine

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

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

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+Ambient

Ambient

Jeff Chastine

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

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 (cdand ld)
- Specular color (csand ls)
- Ambient color (caand la)
- Emit color (ceand le)
- cd* ld = [cd.r*ld.r, cd.g*ld.g, cd.b*ld.b] // R, G, B

Jeff Chastine

General Lighting

- Primary vectors
- l – the incoming light vector
- n – the normal of the plane/vertex
- r – the reflection vector
- v – the viewpoint (camera)

v

n

l

r

θ

θ

Jeff Chastine

LambertianReFlectance(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

n

l

θ

Jeff Chastine

LambertianReFlectance(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

3 parts (R, G, B)

scalar

n

l

θ

Note: final_colordiffusehas R, G, B

Jeff Chastine

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

h

v

n

r

l

θ

θ

Jeff Chastine

BLINN-PHONG Reflection(Specular Component)

- - which is really Blinn’s contribution to the original Phong model

h

v

n

r

l

θ

θ

Note: vectors should be normalized

Jeff Chastine

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

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

Final Color

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

final_colordiffuse

final_colorspecular

final_colorambient

final_coloremit

final_color

+

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

Jeff Chastine

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

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

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

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

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

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

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

Jeff Chastine

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