[SOLVED] CS Graphics for Games CPI 411

Graphics for Games CPI 411
2/18/2021

Todays Contents
Solution of Lab#5 (Demo)
Reflection & Refraction
Quiz#5 (15 min) on Chapter 7
2/18/2021

Review: Skybox
Skybox is a Cube Mapping, which is one of environment maps.
Vertex Shader: Calculate the incident vector as the texture coordinate.
output.TextureCoordinate = VertexPosition.xyz CameraPosition;
Pixel Shader: Use the texCUBE function. SkyBoxSamplerisasamplerCUBE
texCUBE(SkyBoxSampler, normalize(input.TextureCoordinate));

2/18/2021

Overview
Reflection & Refraction BasicReflection
BasicRefraction
Dispersion
Fesnel
Peter Wonka
4

2/18/2021
REFLECTION

Reflection.fx
I : incident vector (negative view vector)
R: Reflection vector of I ; R = reflect (I, N)
Pixel Shader:
SetthetexturecoordinateasR(insteadofI)
Lerpthecolorsofreflection(texCUBE)andmodelstexture(tex2D) N
2/18/2021
I

R

Sample Movie
2/18/2021

2/18/2021
REFRACTION

Refract.fx
I : incident vector (negative view vector)
R: Refract vector of I with refraction factor; R = refract (I, N, etaRatio)
https://msdn.microsoft.com/en-us/library/windows/desktop/bb509640(v=vs.85).aspx
Pixel Shader:
SetthetexturecoordinateasR(insteadofI)
Lerptherefraction(texCUBE)andmodelstexture(tex2D)
Snells Law: 1 sin 1 = 2 sin T
2/18/2021

Definition of refract Parameter = ratio of indices of refraction
float3 refract(float3 I, float3 N, float etaRatio)
{
float cosI = dot(-I, N);
float cosT2 = 1.0f etaRatio * etaRatio * (1.0f cosI * cosI);
float3 T = etaRatio * I +
((etaRatio * cosI sqrt(abs(cosT2))) * N); return T * (float3)(cosT2 > 0);
}
10

Sample Movie
2/18/2021

2/18/2021
FRESNEL EFFECT

Fresnel Effect
E.g. water surface
ifyoulookstraightdownyoucanseeafish
ifyoulookfromsteeperangleyouseereflectionofsky
Simplified Version:
reflectionCoefficient = rC =
max(0, min(1, bias + pow(1 + dot(I, N))power ))
IandNcoincidentrCshouldbe~0
IandNclosetoboundaryanglerCshouldbe~1
Cfinal = rC * Creflected + (1-rC) * Crefracted
13

Sample Movie
2/18/2021

2/18/2021
CHROMATIC DISPERSION

Chromatic Dispersion
Refraction Index Depends on Wavelength
Lookup Red, Green and Blue values at different locations in the reflective environment map
16

Sample Movie
2/18/2021

Dispersion v2
2/18/2021

Fresnel & Dispersion FX
Variables: (controlled by user keyboard input in test program)
float3 etaRatio: Ratio of indices of refraction for red, green, and blue light (packed into one float3)
float fresnelPower: Fresnel power float fresnelScale: Fresnel scale float fresnelBias: Fresnel bias
2/18/2021

Fresnel & Dispersion
Vertex Shader

TRed = refract(I, N, etaRatio.x); TGreen = refract(I, N, etaRatio.y); TBlue = refract(I, N, etaRatio.z);
reflectionFactor =
fresnelBias + fresnelScale * pow(1 + dot(I, N), fresnelPower);
Pixel Shader:
float4 refractedColor;
refractedColor.r = texCUBE(environmentMap, TRed).r; refractedColor.g = texCUBE(environmentMap, TGreen).g; refractedColor.b = texCUBE(environmentMap, TBlue).b; refractedColor.a = 1;
color = lerp(refractedColor, reflectedColor, reflectionFactor); 2/18/2021

Next
Reading Homework
CgTutorialChapter8(BumpMap) http://http.developer.nvidia.com/CgTutorial/cg_tutorial_chapter08.html
Lab #6 (Reflection)
Quiz#5 (Skybox)
2/18/2021