1 Lecture 13: Environment and Bump Mapping Prof. Aaron Lanterman School of Electrical and Computer Engineering Georgia Institute of Technology Real-time graphics has come a long way Slide from from “Teaching Cg” Powerpoint presentation: developer.nvidia.com/object/cg_tutorial_teaching.html The Cg Tutorial • Can get Cg Toolkit, example code, etc. here: http://developer.nvidia.com/object/cg_tutorial_home.html Image from “Teaching Cg” Powerpoint presentation: developer.nvidia.com/object/cg_tutorial_teaching.html Nice framework for experimentation Image from “Teaching Cg” Powerpoint presentation: developer.nvidia.com/object/cg_tutorial_teaching.html2 Cube maps Images from “OpenGL Cube Map Texturing,” developer.nvidia.com/object/cube_map_ogl_tutorial.html Back Front Right Bottom Left Top texCUBE((samplerCUBE) envMap,(float3) vec) Reflection and refraction € θI€ θR€ θI€ θTIncident vector I Refracted vector T Incident vector I Reflected vector R Normal vector N Normal vector N € θI=θR€ η1sin(θI) =η2sin(θT)T=refract(I,N,etaRatio) R=reflect(I,N) € η1/η2etaRatio= € η1€ η2Cg vertex shader for reflective mapping void C7E1v_reflection(float4 position : POSITION, float2 texCoord : TEXCOORD0, float3 normal : NORMAL, out float4 oPosition : POSITION, out float2 oTexCoord : TEXCOORD0, out float3 R : TEXCOORD1, uniform float3 eyePositionW, uniform float4x4 modelViewProj, uniform float4x4 modelToWorld) { oPosition = mul(modelViewProj, position); oTexCoord = texCoord; // Compute position and normal in world space float3 positionW = mul(modelToWorld, position).xyz; float3 N = mul((float3x3)modelToWorld, normal); N = normalize(N); // Compute the incident and reflected vectors float3 I = positionW - eyePositionW; R = reflect(I, N); } From “The Cg Tutorial,” p. 177 Cg pixel shader for reflective mapping void C7E2f_reflection(float2 texCoord : TEXCOORD0, float3 R : TEXCOORD1, out float4 color : COLOR, uniform float reflectivity, uniform sampler2D decalMap, uniform samplerCUBE environmentMap) { // Fetch reflected environment color float4 reflectedColor = texCUBE(environmentMap, R); // Fetch the decal base color float4 decalColor = tex2D(decalMap, texCoord); color = lerp(decalColor, reflectedColor, reflectivity); } From “The Cg Tutorial,” p. 1803 Different indices of refraction Around water (1.333) 0.8 Images from Thomas Kerwin, “Refraction in OpenGL,” www.cse.ohio-state.edu/~kerwin/refraction.html Vacuum: 1.0 Air: 1.0003 Water: 1.333 Glass: 1.5 (ordinary window glass) Plastic: 1.5 Diamond: 2.417 Data from “The Cg Tutorial,” p. 184 Cg vertex shader for refractive mapping void C7E3v_refraction(float4 position : POSITION, float2 texCoord : TEXCOORD0, float3 normal : NORMAL, out float4 oPosition : POSITION, out float2 oTexCoord : TEXCOORD0, out float3 T : TEXCOORD1, uniform float etaRatio, uniform float3 eyePositionW, uniform float4x4 modelViewProj, uniform float4x4 modelToWorld) { oPosition = mul(modelViewProj, position); oTexCoord = texCoord; // Compute position and normal in world space float3 positionW = mul(modelToWorld, position).xyz; float3 N = mul((float3x3)modelToWorld, normal); N = normalize(N); // Compute the incident and refracted vectors float3 I = positionW - eyePositionW; T = refract(I, N, etaRatio); } From “The Cg Tutorial,” p. 187 Cg pixel shader for refractive mapping void C7E4f_refraction(float2 texCoord : TEXCOORD0, float3 T : TEXCOORD1, out float4 color : COLOR, uniform float transmittance, uniform sampler2D decalMap, uniform samplerCUBE environmentMap) { // Fetch the decal base color float4 decalColor = tex2D(decalMap, texCoord); // Fetch refracted environment color float4 refractedColor = texCUBE(environmentMap, T); // Compute the final color color = lerp(decalColor, refractedColor, transmittance); } From “The Cg Tutorial,” p. 188 Chromatic dispersion € θIRefracted vectors Incident vector I Normal vector N T blue T red T green Without CD With CD Images from Thomas Kerwin, “Refraction in OpenGL,” www.cse.ohio-state.edu/~kerwin/refraction.html4 Fresnel effect € reflectCoeff = max(0, min(1,bias + scale(1 + I • N)power))€ Cfinal= reflectCoeff × Creflected+ (1− reflectCoeff )Crefracted• Some light reflects and some refracts • Think about looking into water – At shallow angles, a lot of reflection and little refraction – Looking straight in, a lot of refraction and a little reflection • Empirical approximation: From “The Cg Tutorial,” p. 189 Bump mapping Drawing from Søren Dreijer, “Bump Mapping Using Cg (3rd Edition),” www.blacksmith-studios.dk/projects/downloads/bumpmapping_using_cg.php Images from Paul Baker, “Simple Bumpmapping,” www.paulsprojects.net/tutorials/simplebump/simplebump.html Bump mapping examples Height map Normal map Top row from Wikipedia entry on “bump mapping” Bottom row from Søren Dreijer, “Bump Mapping Using Cg (3rd Edition),” www.blacksmith-studios.dk/projects/downloads/bumpmapping_using_cg.php Shader effect movies • Bump mapping demo with the Cimg library http://video.google.com/videoplay?docid=1570416667092534064 • Bump mapping and reflective textures – (HLEH - Half Life mod???) http://www.youtube.com/watch?v=FmpyHc6hXc4 • Bump mapping on the Nintendo DS http://www.youtube.com/watch?v=6ypt5JE-ofg5 Storing normals in textures • Textures don’t have to store color; we can store other things as well, like normals – Use r, g, b components to store, x, y, z of normal • Problem: Textures take [0,1] values; normals need [-1,1] values • Easy solution: “Range Compression” colorComponent = 0.5 * normalComponent + 0.5; normalComponent = 2 * (colorComponent - 0.5); From “The Cg Tutorial,” p. 202 Creating normal map from height field • Height field H(u,v) € normal =Hg− Hr,Hg− Ha,1( )Hg− Hr,Hg− Ha,1( )€ Hg€ Hr€ Ha• In flat regions, normal is (0,0,1), i.e. pointing “up” From “The Cg Tutorial,” p. 203 Cg vertex shader for bump mapping void C8E1v_bumpWall(float4 position : POSITION, float2 texCoord : TEXCOORD0, out float4 oPosition : POSITION, out float2 oTexCoord : TEXCOORD0, out float3 lightDirection : TEXCOORD1, uniform float3 lightPosition, // Objectspace uniform float4x4 modelViewProj) { oPosition =
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