Lighting and Shading University of California Riverside Why we need shading Suppose we build a model of a red sphere We get something like But we want - lighting facing light shadow Shading Why does a real sphere look like this? Shading - lighting Why does a real sphere look like this? facing light shadow Shading - material properties shiny matte Image source: [1] Shading - viewing location What if I move? Image source: [1] Shading - surface orientation well lit poorly lit Image source: [1] General rendering Based on physics conservation of energy Surfaces can absorb light emit light reflect light transmit light Idealized light sources ambient point light spotlight directional light Ambient light Achieve uniform light level No shadows Same light level everywhere Point light Light emitted from a point p Uniform in all directions 1 Falls off with distance: `(x) = L kx − pk2 Point light - limitations rapid falloff no light sharp shadow Soft shadows Spotlight Light emitted from a point p Emited in a cone Brightest in middle of cone Falls off with distance Spotlight p cose φ `(x) = L kx − pk2 θ cos φ φ x −θ θ Spotlight - exploring e e = 1 −θ θ e = 20 e = 60 Directional light Light source at infinity Rays come in parallel No falloff Characterized by direction Lambertian reflection model Image source: [1] Emitted a I = RL0 I = LR h RE Lambertian reflection model w a n l θ n l w h Light Absorbed Intensity LL0 Energy E = Lwa E = L0wh a I = LR h Lambertian reflection model w a n l θ n l w h Light Absorbed Emitted Intensity LL0 I = RL0 Energy E = Lwa E = L0wh RE Lambertian reflection model w a n l θ n l w h Light Absorbed Emitted a Intensity LL0 I = RL0 I = LR h Energy E = Lwa E = L0wh RE = LRcos θ = LRn · l Avoid bug: I = LR max(n · l; 0) Lambertian reflection model a n l θ n l θ a θ h a I = LR h = LRn · l Avoid bug: I = LR max(n · l; 0) Lambertian reflection model a n l θ n l θ a θ h a I = LR = LRcos θ h Avoid bug: I = LR max(n · l; 0) Lambertian reflection model a n l θ n l θ a θ h a I = LR = LRcos θ = LRn · l h Lambertian reflection model a n l θ n l θ a θ h a I = LR = LRcos θ = LRn · l h Avoid bug: I = LR max(n · l; 0) Ambient reflection I = LR max(n · l; 0) l Surfaces facing away from the light will be totally black n Ambient reflection I = LaRa + LdRd max(n · l; 0) l All surfaces get the same amount of ambient light n Phong reflection model Image source: [1] Phong reflection model Efficient n v Reasonably realistic l r 3 components 4 vectors Phong reflection model I = Ia + Id + Is α = RaLa + RdLd max(n · l; 0) + RsLs max(cos φ, 0) Ambient reflection Ia = RaLa 0 ≤ Ra ≤ 1 Diffuse reflection Diffuse reflection a n l θ a θ h Id = RdLd max(n · l; 0) Specular reflection Ideal reflector θi = θr r is the mirror reflection direction Specular reflection Specular surface specular reflection is strongest in reflection direction Specular reflection α Is = RsLs max(cos φ, 0) specular reflection drops off with increasing φ Phong reflection model I = Ia + Id + Is α = RaLa + RdLd max(n · l; 0) + RsLs max(v · r; 0) n v l r Attribution [1] Andrea Fisher Fine Pottery. jody-folwell-jar05big.jpg. https://www.eyesofthepot.com/santa-clara/jody folwell..