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CS361Week 8 - Wednesday
Last time
What did we talk about last time? Textures
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
Questions?
Project 2
Radiometry
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]
Radiometric quantities
We'll be interested in the following radiometric quantitiesQuantity Unit
Radiant energy joule (J)
Radiant flux watt (W)
Irradiance W/m2
Radiant intensity W/sr
Radiance W/(m2sr)
Concrete examples
Radiant flux: energy per unit time (power) Irradiance: energy per unit time through a
surface Intensity: energy per unit time per steradian
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
Photometry
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
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 screensRadiometric Quantity
Unit Photometric Quantity
Unit
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
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.)
Lighting in SharpDX
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
SharpDX 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
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
Ambient light declarations
float4x4 World;float4x4 View;float4x4 Projection;
float4 AmbientColor = float4(1, 1, 1, 1);float AmbientIntensity;
struct VertexShaderInput{
float4 Position : SV_Position;};
struct VertexShaderOutput{
float4 Position : SV_Position;};
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;}
Ambient light pixel shader and technique
float4 PixelShaderFunction(VertexShaderOutput input) : SV_Target{
return AmbientColor * AmbientIntensity;}
technique Ambient{
pass Pass1{
VertexShader = compile vs_2_0 VertexShaderFunction();
PixelShader = compile ps_2_0 PixelShaderFunction();}
}
Directional lights in SharpDX 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
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;float4x4 WorldInverseTranspose;
float4 AmbientColor = float4(1, 1, 1, 1);float AmbientIntensity = 0.1;
float3 DiffuseLightDirection = float3(1, 1, 0);float4 DiffuseColor = float4(1, 1, 1, 1);float DiffuseIntensity = 0.7;
struct VertexShaderInput{
float4 Position : SV_POSITION;float3 Normal : NORMAL;
};
struct VertexShaderOutput{
float4 Position : SV_POSITION;float4 Color : COLOR;
};
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);float3 normal = mul(input.Normal,
(float3x3)WorldInverseTranspose);float lightIntensity = dot(normalize(normal),
normalize(DiffuseLightDirection));output.Color = saturate(DiffuseColor * DiffuseIntensity *
lightIntensity);return output;
}
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) : SV_Target{
return saturate(input.Color + AmbientColor * AmbientIntensity);
}
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
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 = 3.14159265f;
float4 AmbientColor = float4(1, 1, 1, 1);float AmbientIntensity = 0.1;
float3 DiffuseLightDirection = float3(1, 1, 0);float4 DiffuseColor = float4(1, 1, 1, 1);float DiffuseIntensity = 0.7;
float Shininess;float4 SpecularColor = float4(1, 1, 1, 1);float SpecularIntensity = 0.5;
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 : SV_POSITION;float3 Normal : NORMAL;
};
struct VertexShaderOutput{
float4 Position : SV_POSITION;float4 Color : COLOR;float3 Normal : NORMAL;float4 WorldPosition : POSITIONT;
};
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;
}
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 samefloat4 PixelShaderFunction(VertexShaderOutput input) : SV_Target{
float3 light = normalize(DiffuseLightDirection);float3 normal = normalize(input.Normal);float3 reflect = normalize(2 * dot(light, normal) * normal –
light);float3 view = normalize(input.WorldPosition - Camera);float dotProduct = dot(reflect, view);float4 specular = (8 + Shininess) / (8 * PI) * SpecularIntensity *
SpecularColor * max(pow(dotProduct, Shininess), 0) * length(input.Color);
return saturate(input.Color + AmbientColor * AmbientIntensity + specular);
}
Point lights in SharpDX
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
Point light declarations
We add light positionfloat4x4 World;float4x4 View;float4x4 Projection;float4x4 WorldInverseTranspose;float3 LightPosition;float3 Camera;
static const float PI = 3.14159265f;
float4 AmbientColor = float4(1, 1, 1, 1);float AmbientIntensity = 0.1f;float LightRadius = 50;
float4 DiffuseColor = float4(1, 1, 1, 1);float DiffuseIntensity = 0.7;
float Shininess;float4 SpecularColor = float4(1, 1, 1, 1);float SpecularIntensity = 0.5f;
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 : SV_POSITION;float3 Normal : NORMAL;
};
struct VertexShaderOutput{
float4 Position : SV_POSITION;float4 WorldPosition : POSITIONT;float3 Normal : NORMAL;
};
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;
}
Point light pixel shader
Lots of junk in herefloat4 PixelShaderFunction(VertexShaderOutput input) : SV_Target{
float3 normal = normalize(input.Normal);float3 lightDirection = LightPosition –
(float3)input.WorldPosition;float intensity = pow(1.0f –
saturate(length(lightDirection)/LightRadius), 2); lightDirection = normalize(lightDirection); //normalize afterfloat3 view = normalize(Camera - (float3)input.WorldPosition);float diffuseColor = dot(normal, lightDirection); float3 reflect = normalize(2 * diffuseColor * normal –
lightDirection); float dotProduct = dot(reflect, view);float specular = (8 + Shininess) / (8 * PI) * SpecularIntensity *
SpecularColor * max(pow(dotProduct, Shininess), 0) * length(diffuseColor);
return saturate(diffuseColor + AmbientColor * AmbientIntensity + specular);
}
Quiz
Upcoming
Next time…
BRDFs Implementing BRDFs Texture mapping in shaders
Reminders
Finish reading Chapter 7 Summer REU opportunity:
Machine learning at the Florida Institute of Technology
Deadline March 31, 2015 http://www.amalthea-reu.org/