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CS-C3100 Computer Graphics 13.1 A simple shading model for Ray Tracing

Jaakko Lehtinen with lots of material from Frédo Durand

Hen

rik W

ann

Jens

en

In This Video

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• A simple shading model for a simple ray tracer – Point-light illumination – Shadows – Reflections – Refractions

NVIDIA

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Today – Ray Tracing(Indirect illumination)

Shadows

ReflectionsRefractions

(Caustics)

Hen

rik W

ann

Jens

en

A Very Simple Shading Model

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• A subset of “Whitted ray tracing” – Turner Whitted, An Improved Illumination Model for

Shaded Display, Comm. ACM, 1980

• Just for illustration really, we’ll be looking at other models shortly

RoRd

N

A Very Simple Shading Model

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• A subset of “Whitted ray tracing” – Turner Whitted, An Improved Illumination Model for

Shaded Display, Comm. ACM, 1980 • Light towards the eye I is...

RoRd

NL

direct lightingI = kd max(0,L ·N)V (L)

A Very Simple Shading Model

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• A subset of “Whitted ray tracing” – Turner Whitted, An Improved Illumination Model for

Shaded Display, Comm. ACM, 1980 • Light towards the eye I is...

RoRd

NLR

+ ks I(R)I = kd kl max(0,L · N)

mirror reflection

direct lightingI = kd max(0,L ·N)V (L)

A Very Simple Shading Model

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• A subset of “Whitted ray tracing” – Turner Whitted, An Improved Illumination Model for

Shaded Display, Comm. ACM, 1980 • Light towards the eye I is...

RoRd

NLR

T

+ ks I(R)+ kt I(T )

I = kd kl max(0,L · N)mirror reflection

mirror refraction

direct lightingI = kd max(0,L ·N)V (L)

+ ks I(R)

A Very Simple Shading Model

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• A subset of “Whitted ray tracing” – Turner Whitted, An Improved Illumination Model for

Shaded Display, Comm. ACM, 1980 • Light towards the eye I is...

RoRd

NLR

T

+ kt I(T )

I(R) is light from mirror direction R I(T) is refracted light from direction T kd, ks, and kt are diffuse, specular and refraction coefficients

I = kd kl max(0,L · N)mirror reflection

mirror refraction

direct lightingI = kd max(0,L ·N)V (L)

Our Placeholder Model

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• V(L) is visibility of light source (0 or 1) • kd, ks, kt are material properties

– ka global constant, kl is light color • We are ignoring (e.g.)

– Specular reflection from the light (only diffuse N.L) – Distance falloff (only angle of normal and L)

+ ks I(R)+ kt I(T )

kd = diffuse coefficient (“color”)

ks = specular coefficient (“color”)

kt mirror refraction coefficient

+ kd ka ambient lighting

I = kd kl max(0,L · N)I = kd max(0,L ·N)V (L)

Where Do These Come From?

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• “Light incident from reflected direction” • “Light incident from refracted direction” • Light going towards the camera

• We’ll recurse and use the same function again

+ ks I(R)+ kt I(T )

kd = diffuse coefficient (“color”)

ks = specular coefficient (“color”)

kt mirror refraction coefficient

+ kd ka ambient lighting

I = kd kl max(0,L · N)I = kd max(0,L ·N)V (L)

Where Do These Come From?

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• “Light incident from reflected direction” • “Light incident from refracted direction” • Light going towards the camera

• We’ll recurse and use the same function again

+ ks I(R)+ kt I(T )

kd = diffuse coefficient (“color”)

ks = specular coefficient (“color”)

kt mirror refraction coefficient

+ kd ka ambient lighting

I = kd kl max(0,L · N)I = kd max(0,L ·N)V (L)

Where Do These Come From?

10

• “Light incident from reflected direction” • “Light incident from refracted direction” • Light going towards the camera

• We’ll recurse and use the same function again

+ ks I(R)+ kt I(T )

kd = diffuse coefficient (“color”)

ks = specular coefficient (“color”)

kt mirror refraction coefficient

+ kd ka ambient lighting

I = kd kl max(0,L · N)I = kd max(0,L ·N)V (L)

What Does It Look Like?

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Turner Whitted

Good Read!

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Turner Whitted thinks back to the days of his discovery

What Does It Look Like?

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Simple NVIDIA Optix sample