02/04/03 Page 1 Rendering Visibility Lighting Texturing

02/04/03 Page 2 1. Application/Scene –Description of the contents of the 3D world –Object Visibility Check including possible Occlusion Culling 2. Geometry –Transforms (rotation, translation, scaling) –Transform from Model Space to View Space –View Projection –Trivial Accept/Reject Culling –Transform to Clip Space –Clipping –Transform to Screen Space 3. Triangle Setup –Back-face Culling (or can be done in view space before lighting) –Scan-Line Conversion 4. Rendering / Rasterization –Shading –Texturing –Fog –Alpha Translucency Tests –Depth Buffering –Z-buffer Pipeline

02/04/03 Page 3 CPU vs. GPU From Move Object and Camera (AI, Realistic Physics) CPU Scene Level Calculations, High order surface tessellation CPU GPU TransformsCPU GPU LightingCPU GPU Triangle Setup and ClippingCPU GPU Rendering Graphics Processor GPU

02/04/03 Page 4 Visibility Object Visibility Tests / Occlusion Tests Bounding boxes –Approximate objects for quick tests Area occluded by bounding box of A A Note that B is not fully occluded by object A B

02/04/03 Page 5 Visibility Object Visibility Tests / Occlusion Tests QuadTrees –Partition space

02/04/03 Page 6 Visibility Object Visibility Tests / Occlusion Tests QuadTrees/OctTrees –Partition 3D space

02/04/03 Page 7 Visibility Object Visibility Tests / Occlusion Tests QuadTrees/OctTrees/BSP –Partition space to create a binary tree

02/04/03 Page 8 Visibility Object Visibility Tests / Occlusion Tests Portals

02/04/03 Page 9 View Space Near Clipping Plane Far Clipping Plane View Frustum View point Polygon clipping

02/04/03 Page 10 Shading models Simple model has 3 basic elements –Diffuse (direct reflection) –Ambient (reflected and scattered light from the environment) –Specular (highlights from surface) Notes –not physically-based and inaccurate –nevertheless, a decent approximation –fast to compute

02/04/03 Page 11 Shading models Diffuse (Lambertian) Reflection –Dull, matte surfaces –Viewer position independent –Dependent on position and intensity of source Reflection is product of light ray L and surface normal N Light (I p ) N L N L N L But this doesn’t look very good … lighting is too harsh (See this example)example I = I p k d (N L) ( k d is coeff. of diffusion )

02/04/03 Page 12 Ambient Light So we add ambient light –Constant term –Crude approximation of light scattering in scene –Independent of object, light, or viewer position From I = I a k a + I p k d (N L)

02/04/03 Page 13 Specular Reflection To get more accurate and model highlights off the surface, we add specular reflection. This adds reflection proportional to cos n α I = I a k a C a + I p [k d C d (N L) + k s C s (R V)] (C is object color) Light (I p ) N L R V Reflected ray To viewer

02/04/03 Page 14 Shininess: 0 Shininess Strength: 0 Shininess: 0 Shininess Strength: 33 Shininess: 33 Shininess Strength: 66 Shininess: 66 Shininess Strength: 100 Shininess: 100 Shininess Strength: 100 From Specular coefficients

02/04/03 Page 15 All together Note: mach banding in Gouraud FlatGouraudPhong

02/04/03 Page 16 Ambient Point sources Directional lights (infinite source) Spot lights Area lights Local lights Lights X

02/04/03 Page 17 Texture uv coordinates 0,1 1,1 0,01,0 0,11,1 1,0 0,0

02/04/03 Page 18 From Gamedev.net Mip Mapping R GB R GB R GB

02/04/03 Page 19 Multi passes Provides application of “textures” to texttures Quake III uses 10 passes: –(passes 1 - 4: accumulate bump map) –pass 5: diffuse lighting –pass 6: base texture (with specular component) –(pass 7: specular lighting) –(pass 8: emissive lighting) –(pass 9: volumetric/atmospheric effects) –(pass 10: screen flashes) (From: Brian Hook, course 29 notes at SIGGRAPH '98)

02/04/03 Page 20 Bump Mapping

02/04/03 Page 21 Reflection and refraction From Snell’s Law : ir 1 *sin ( 1 ) = ir 2 *sin ( 2 )

02/04/03 Page 22 Environment Mapping Environment mapped onto cube, then projected onto object

02/04/03 Page 23 Light mapping X = From Pre-computed “texture map” Simulates light sources

02/04/03 Page 24 Alpha blending FinalColor = SourcePixelColor * SourceBlendFactor + DestPixelColor * DestBlendFactor From

02/04/03 Page 25 Z buffer Each pixel in the buffer contains the distance from the viewpoint of the object rendered at that pixel If the next object to be drawn at that pixel is further then the value at the pixel, then don’t write the pixel. Note: ATI Radeon’s Hierarchal Z-buffering

02/04/03 Page 26 Reading 3D pipeline tutorial