1. Week 8 - Wednesday
CS361

2. Last time What did we talk about last time? Textures Bump mapping
Volume textures
Cube maps
Texture caching and compression
Procedural texturing
Texture animation
Material mapping
Alpha mapping
Bump mapping
Normal maps
Parallax mapping
Relief mapping
Heightfield texturing

3. Questions?

4. Project 2

5. Radiometry

6. Radiometry
Radiometry is the measurement of electromagnetic radiation (for us, specifically light)
Light is the flow of photons
We'll generally think of photons as particles, rather than waves
Photon characteristics
Frequency ν = c/λ (Hertz)
Wavelength λ = c/ν (meters)
Energy Q = hν (joules) [h is Planck's constant]

7. Radiometric quantities
We'll be interested in the following radiometric quantities
Quantity
Unit
Radiant energy
joule (J)
Radiant flux
watt (W)
Irradiance
W/m2
Radiant intensity
W/sr
Radiance
W/(m2sr)

8. Concrete examples Radiant flux: energy per unit time (power)
Irradiance: energy per unit time through a surface
Intensity: energy per unit time per steradian

9. Radiance
The radiance L is what we care about since that's what sensors detect
We can think of radiance as the portion of irradiance within a solid angle
Or, we can think of radiance as the portion of a light's intensity that flow through a surface
Radiance doesn't change with distance

10. Photometry

11. Photometry Radiometry just deals with physics
Photometry takes everything from radiometry and weights it by the sensitivity of the human eye
Photometry is just trying to account for the eye's differing sensitivity to different wavelengths

12. Photometric units
Because they're just rescalings of radiometric units, every photometric unit is based on a radiometric one
Luminance is often used to describe the brightness of surfaces, such as LCD screens
Radiometric Quantity
Unit
Photometric Quantity
Radiant energy
joule (J)
Luminous energy
talbot
Radiant flux
watt (W)
Luminous flux
lumen
Irradiance
W/m2
Illuminance
lux
Radiant intensity
W/sr
Luminous intensity
candela
Radiance
W/(m2sr)
Luminance
nit

13. Colorimetry
Colorimetry is the science of quantifying human color perception
The CIE defined a system of three non-monochromatic colors X, Y, and Z for describing the human perceivable color space
RGB is a transform from these values into monochromatic red, green, and blue colors
RGB can only express colors in the triangle
As you know, there are others (HSV, HSL, etc.)

14. Lighting in MonoGame

15. Types of lights Real light behaves consistently (but in a complex way)
For rendering purposes, we often divide light into categories that are easy to model
Directional lights (like the sun)
Omni lights (located at a point, but evenly illuminate in all directions)
Spotlights (located at a point and have intensity that varies with direction)
Textured lights (give light projections variety in shape or color)
Similar to gobos, if you know anything about stage lighting

16. MonoGame lights
With a programmable pipeline, you can express lighting models of limitless complexity
The old DirectX fixed function pipeline provided a few stock lighting models
Ambient lights
Omni lights
Spotlights
Directional lights
All lights have diffuse, specular, and ambient color
Let's see how to implement these lighting models with shaders

17. Ambient lights Ambient lights are very simple to implement in shaders
We've already seen the code
The vertex shader must simply transform the vertex into clip space (world x view x projection)
The pixel shader colors each fragment a constant color
We could modulate this by a texture if we were using one

18. Ambient light declarations
float4x4 World;
float4x4 View;
float4x4 Projection;
float4 AmbientColor = float4(1, 0, 0, 1);
float AmbientIntensity = 0.5;
struct VertexShaderInput {
float4 Position : POSITION0; };
struct VertexShaderOutput

19. Ambient light vertex shader
VertexShaderOutput VertexShaderFunction(VertexShaderInput input) {
VertexShaderOutput output;
float4 worldPosition = mul(input.Position, World);
float4 viewPosition = mul(worldPosition, View);
output.Position = mul(viewPosition, Projection);
return output; }

20. Ambient light pixel shader and technique
float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0 {
return AmbientColor * AmbientIntensity; }
technique Ambient {
pass Pass1 {
VertexShader = compile VS_SHADERMODEL
VertexShaderFunction();
PixelShader = compile PS_SHADERMODEL PixelShaderFunction(); }

21. Directional lights in MonoGame
Directional lights model lights from a very long distance with parallel rays, like the sun
It only has color (specular and diffuse) and direction
They are virtually free from a computational perspective
Directional lights are also the standard model for BasicEffect
You don't have to use a shader to do them
Let's look at a diffuse shader first

22. Diffuse light declarations
We add values for the diffuse light intensity and direction
We add a WorldInverseTranspose to transform the normals
We also add normals to our input and color to our output
float4x4 World;
float4x4 View;
float4x4 Projection;
float4 AmbientColor = float4(1, 1, 1, 1);
float AmbientIntensity = 0.1;
float4x4 WorldInverseTranspose;
float4 DiffuseLightDirection = float4(1, 2, 0, 0);
float4 DiffuseColor = float4(1, .5, 0, 1);
float DiffuseIntensity = 1.0;
struct VertexShaderInput {
float4 Position : POSITION0;
float4 Normal : NORMAL0; };
struct VertexShaderOutput {
float4 Color : COLOR0;

23. Diffuse light vertex shader
Color depends on the surface normal dotted with the light vector
VertexShaderOutput VertexShaderFunction(VertexShaderInput input){
VertexShaderOutput output;
float4 worldPosition = mul(input.Position, World);
float4 viewPosition = mul(worldPosition, View);
output.Position = mul(viewPosition, Projection);
float4 normal = mul(input.Normal, WorldInverseTranspose);
float lightIntensity = dot(normal,
normalize(DiffuseLightDirection));
output.Color = saturate(DiffuseColor * DiffuseIntensity *
lightIntensity);
return output; }

24. Diffuse light pixel shader
No real differences here
The diffuse color and ambient colors are added together
The technique is exactly the same
float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0 {
return saturate(input.Color + AmbientColor * AmbientIntensity); }

25. Specular lighting
Adding a specular component to the diffuse shader requires incorporating the view vector
It will be included in the shader file and be set as a parameter in the C# code

26. Specular light declarations
The camera location is added to the declarations
As are specular colors and a shininess parameter
float4x4 World;
float4x4 View;
float4x4 Projection;
float4x4 WorldInverseTranspose;
float3 Camera;
static const float PI = f;
float4 AmbientColor = float4(1, 1, 1, 1);
float AmbientIntensity = 0.1;
float3 DiffuseLightDirection;
float4 DiffuseColor = float4(1, 1, 1, 1);
float DiffuseIntensity = 0.7;
float Shininess = 20;
float4 SpecularColor = float4(1, 1, 1, 1);
float SpecularIntensity = 0.5;

27. Specular light structures
The output adds a normal so that the half vector can be computed in the pixel shader
A world position lets us compute the view vector to the camera
struct VertexShaderInput {
float4 Position : POSITION0;
float3 Normal : NORMAL0;  };
struct VertexShaderOutput {
float4 Color : COLOR0;
float3 Normal : NORMAL0;
float4 WorldPosition : POSITIONT;

28. Specular vertex shader
The same computations as the diffuse shader, but we store the normal and the transformed world position in the output
VertexShaderOutput VertexShaderFunction(VertexShaderInput input) {
VertexShaderOutput output;
float4 worldPosition = mul(input.Position, World);
output.WorldPosition = worldPosition;
float4 viewPosition = mul(worldPosition, View);
output.Position = mul(viewPosition, Projection);
float3 normal = normalize(mul(input.Normal,
(float3x3)WorldInverseTranspose));
float lightIntensity = dot(normal, normalize(DiffuseLightDirection));
output.Color = saturate(DiffuseColor * DiffuseIntensity *
lightIntensity);
output.Normal = normal;
return output; } 

29. Specular pixel shader
Here we finally have a real computation because we need to use the pixel normal (which is averaged from vertices) in combination with the view vector
The technique is the same
float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0 {
float3 light = normalize(DiffuseLightDirection);
float3 normal = normalize(input.Normal);
float3 reflect = normalize(2 * dot(light, normal) * normal - light );
float3 view = normalize(Camera - (float3)input.WorldPosition);
float dotProduct = dot(reflect, view);
float4 specular = (8 + Shininess) / (8 * PI) * SpecularIntensity * SpecularColor * pow(saturate(dotProduct), Shininess);
return saturate(input.Color + AmbientColor * AmbientIntensity +
specular); }

30. Point lights in MonoGame
Point lights model omni lights at a specific position
They generally attenuate (get dimmer) over a distance and have a maximum range
DirectX has a constant attenuation, linear attenuation, and a quadratic attenuation
You can choose attenuation levels through shaders
They are more computationally expensive than directional lights because a light vector has to be computed for every pixel
It is possible to implement point lights in a deferred shader, lighting only those pixels that actually get used

31. Point light declarations
We add light position and radius
float4x4 World;
float4x4 View;
float4x4 Projection;
float4x4 WorldInverseTranspose;
float3 LightPosition;
float LightRadius = 100;
float3 Camera;
static const float PI = f;
float4 AmbientColor = float4(1, 1, 1, 1);
float AmbientIntensity = 0.1;
float4 DiffuseColor = float4(1, 1, 1, 1);
float DiffuseIntensity = 0.7;
float Shininess = 20;
float4 SpecularColor = float4(1, 1, 1, 1);
float SpecularIntensity = 0.5;

32. Point light structures
We no longer need color in the output
We do need the vector to the camera from the location
We keep the world location at that fragment
struct VertexShaderInput {
float4 Position : POSITION0;
float3 Normal : NORMAL0; };
struct VertexShaderOutput {
float4 WorldPosition : POSITIONT;

33. Point light vertex shader
We compute the normal and the world position
VertexShaderOutput VertexShaderFunction(VertexShaderInput input) {
VertexShaderOutput output;
float4 worldPosition = mul(input.Position, World);
output.WorldPosition = worldPosition;
float4 viewPosition = mul(worldPosition, View);
output.Position = mul(viewPosition, Projection);
float3 normal = normalize(mul(input.Normal,
(float3x3)WorldInverseTranspose));
output.Normal = normal;
return output; }

34. Point light pixel shader
Lots of junk in here
float4 PixelShaderFunction(VertexShaderOutput input) : COLOR0 {
float3 lightDirection = LightPosition –
(float3)input.WorldPosition;
float3 normal = normalize(input.Normal);
float intensity = pow(1 - saturate(length(lightDirection) /
LightRadius), 2);
lightDirection = normalize(lightDirection);
float3 view = normalize(Camera - (float3)input.WorldPosition);
float diffuseColor = dot(normal, lightDirection) * intensity;
float3 reflect = normalize(2 * diffuseColor * normal –
lightDirection);
float dotProduct = dot(reflect, view);
float4 specular = (8 + Shininess) / (8 * PI) *
SpecularIntensity * SpecularColor * pow(saturate(dotProduct), Shininess) * intensity;
return saturate(diffuseColor + AmbientColor * AmbientIntensity
+ specular); }

35. Quiz

36. Upcoming

37. Next time…
BRDFs
Implementing BRDFs
Texture mapping in shaders

38. Reminders
Finish reading Chapter 7