Week 8 - Wednesday CS361

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

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 quantities Quantity 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 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

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 MonoGame

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

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

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, 0, 0, 1); float AmbientIntensity = 0.5; struct VertexShaderInput { float4 Position : POSITION0; }; struct VertexShaderOutput

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) : COLOR0 { return AmbientColor * AmbientIntensity; } technique Ambient { pass Pass1 { VertexShader = compile VS_SHADERMODEL VertexShaderFunction(); PixelShader = compile PS_SHADERMODEL PixelShaderFunction(); }

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

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;

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; }

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); }

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; 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;

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;

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 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); }

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

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 = 3.14159265f; 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;

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;

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 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); }

Quiz

Upcoming

Next time… BRDFs Implementing BRDFs Texture mapping in shaders

Reminders Finish reading Chapter 7