1	3D Geometric Graphics: Rendering
2	The Rendering Pipeline: from Geometric Model Construction to Image Synthesis Modeling Shapes and their (hierarchical) composition Materials (degrees of diffuse and specular reflection) Behavior: time-varying attributes for each frame or key frame Lighting Directional lights, spot lights, area lights, etc… Specifying the “camera” to define the view volume Position Direction (a vector in 3-space) Orientation about “barrel” of “lens” Field of view (wide-angle to telephoto) via clipping planes Choose perspective or parallel projection ========================================= Rendering: map from 3D scene to 2D image
3	Geometric Modeling Hierarchy
4	Common Light Types c
5	Specifying the Camera Position Direction Orientation Field of View Projection type: perspective or parallel
6	Specifying the Camera 1/2
7	Specifying the Camera 2/2 Eye and camera have a semi-infinite circular cone of vision, aka view volume: must clip what isn’t “inside” Too “expensive” (mathematically) to clip against such a cone Therefore we approximate with rectangular cone/pyramid Further limit to finite pyramid with front and back “clipping planes”
8	Materials Combination of Color Reflective/refractive properties of “material” Maps: texture, bump, environment,… Procedural textures and other kinds of maps
9	Surface Reflection Properties Light reflected depends on Incoming light from light sources or other objects (light source type, color, potential occlusion…) Orientation of surface to that light Orientation of surface to the viewer, including potential occlusion by other surfaces Material properties (color, roughness, reflectivity…) Surface normals Defined for tiny planar or curved “patches” Defines orientation of surface
10	Diffuse and Specular Reflection 1/2 Diffuse is view-angle independent, only angle of surface to light matters (cosine law) Specular is view-angle dependent
11	Specular Reflection in Action
12	Diffuse and Specular Reflection 2/2 Below show varying combinations of specular and diffuse for single light source at upper left of viewer In practice all materials combine diffuse and specular reflection and absorption
13	Announcements Feedback forms Depth vs. breadth syllabus now shifts to more depth and applications areas Variety of backgrounds Yes—hard to have material interesting to everyone all the time… More discussion, less lecture YES Thanks for ideas: Sections More take-homes Other specific comments Continuing to look through—also, email etc. welcome! Experimental, experimental, experimental… Jaron! MacMillan 115—see MOTD. READ HIS “Half-Manifesto” at http://www.wired.com/wired/archive/8.12/lanier_pr.html Link is also on MOTD
14	Critique Works? If so why? If not, how can we fix? Proximity Alignment Repetition Contrast Type expressiveness, appropriateness Graphic elements
15	Non-Global Illumination Models Hidden surface removal means polygons you can’t see are not rendered (both those blocked and those that are back-facing – eliminates >50%) Non-global means that we look at each polygon in isolation, no shadows or interobject reflection. Crude but fast model, standard in graphics cards Flat shading: light calculated once for each polygon, as a function of the angle between its surface normal and the light source (the “faceted look”) Gouraud shading (after Henri Gouraud): average intensity across neighboring polygons to create smooth gradients between them. Phong shading adds specular part by averaging normals, not intensities
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17	"c" c
18	Global Illumination Models Ray tracing (early 1980s) Specular interobject reflection, refraction Radiosity (late 1980s) Diffuse interobject reflection
19	Simple Ray Tracing
20	Shadows
21	Reflections
22	Transmission (Transparency)
23	You know it’s ray tracing when… Reflection, transparency, other light-bouncing effects
24	Yoichiro Kawaguchi, Evolver 1998
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26	Radiosity Iteratively calculate patch-to-patch reflection of light based on their relative geometry and material properties Start with light sources You get: diffuse reflections, color bleeding, soft shadows
27	"v" v
28	Radiosity, Radiosity&Ray Tracing c
29	GTT Simple Robot Exercise Make a simple robot with a head (sphere), body (cylinder), and at least one leg (cube) Scale, rotate and translate each primitive to make the robot. Use at least two lights Group all parts into a Group Node and experiment with scaling, rotating the robot as a whole. DOWNLOAD new GTT (v4.3) http://graphics.cs.brown.edu/ research/gtt/