Announcements Programming Assignment 4 is out No Class Thursday (Office Hrs On Request)

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Announcements Programming Assignment 4 is out No Class Thursday (Office Hrs On Request) Computer Graphics 15-462 1 Procedural Modeling Procedural Terrain…
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Announcements Programming Assignment 4 is out No Class Thursday (Office Hrs On Request) Computer Graphics 15-462 1 Procedural Modeling Procedural Terrain L-Systems Procedural Animation/Behavior COMPUTER GRAPHICS 15-462 04/05/07 Computer Graphics 15-462 2 Database Amplification ã Procedural content generation is attractive because it allows for significant database amplification ã Limited input data produces rich & varied output – ie: Perlin noise function + basic math gives fire, clouds, wood, etc. ã If it can be generated on the fly… – Artist doesn’t have to design it – Don’t need to store/transmit it Computer Graphics 15-462 3 “Implicit” vs. “Explicit” Procedural Models ã Explicit: – Directly generate the points that make up an object – Good for Z-buffer/OpenGL style rendering ã Implicit: – Answer questions about particular points – Isocurve (2D) or Isosurface (3D) – Good for ray-tracing Computer Graphics 15-462 4 Simple Explicit Procedural Model ã Begin with a regular mesh ã Perturb vertex geometry procedurally (typically pseudorandomly) ã Iterate this process until desired shape is achieved ã Very general technique that can also be used to add irregularity (“noise”) to arbitrary mesh objects Computer Graphics 15-462 5 Procedural Terrain ã “Subdivide and displace” Computer Graphics 15-462 6 Midpoint Displacement For Terrain ã Seed corners with values ã Perturb midpoint randomly from mean ã Recurse using a smaller window ã In 2D, best to use “diamond-square” recursion (to prevent axis-aligned artifacts) Computer Graphics 15-462 7 Fractal Noise Terrain ã Use fractal noise to generate terrain ã Can be made tileable over unit square: Ftileable(x,y) = [ F(x,y) * (1-x) * (1-y) + F(x-1,y) * x * (1-y) + F(x-1,y-1) * x * y + F(x,y-1) * (1-x) * y] F.K. Musgrave Computer Graphics 15-462 8 Adding Water F.K. Musgrave ã Use an elevation threshold (z zwater) Computer Graphics 15-462 9 Terrain Example F.K. Musgrave Computer Graphics 15-462 10 Terrain Example F.K. Musgrave Computer Graphics 15-462 11 Terrain Example F.K. Musgrave Computer Graphics 15-462 12 Terragen ã Commercial product (free for personal use) ã Website: http://www.planetside.co.uk/terragen/ ã This image took ~3 minutes to set up Computer Graphics 15-462 13 Hypertexture ã Implicit procedural model ã Treat the isosurface of a function as the boundary of an object ã Above: fractal egg Photo: K. Perlin Computer Graphics 15-462 14 Hypertexture Example K. Perlin Computer Graphics 15-462 15 Hypertexture Example K. Perlin Computer Graphics 15-462 16 Architexture ã Sweep the path of a line drawing with a sphere ã Apply hypertexture to resulting shape K. Perlin Computer Graphics 15-462 17 L-Systems (Background) ã Developed by A. Lindenmayer to model the development of plants ã Based on parallel string-rewriting rules ã Excellent for modeling organic objects and fractals Computer Graphics 15-462 18 L-Systems (Basics) ã Begin with a set of “productions” (replacement rules) and a “seed” axiom ã In parallel, all matching productions are replaced with their right-hand sides ã Ex: – Rules: B- ACA A- B – Axiom: AA – Sequence: AA,BB,ACAACA,BCBBCB,etc. ã Strings are converted to graphic representations via interpretation as turtle graphics commands Computer Graphics 15-462 19 L-Systems (Basic Example) ã Turtle Commands: – Fx: move forward one step, drawing a line – fx: move forward one step, without drawing a line – +x: turn left by angle ∂ – -x: turn right by angle ∂ Computer Graphics 15-462 20 L-Systems (Koch Snowflake) ã Axiom: F-F-F-F ∂:90 degrees ã FF-F+F+FF-F-F+F Computer Graphics 15-462 21 L-Systems (Dragon Curve) ã Axiom:Fl ∂:90 degrees n:10 iterations ã FlFl+Fr+ ã FrFl-Fr- Computer Graphics 15-462 22 L-Systems (Extensions) ã Basic L-Systems have inspired a large number of variations ã Context sensitive: productions look at neighboring symbols ã Bracketed: save/restore state (for branches) ã Stochastic: choose one of n matching productions randomly ã Parametric: variables can be passed between productions Computer Graphics 15-462 23 L-Systems For Plants P. Prusiniewicz ã L-Systems can capture a large array of plant species ã Designing rules for a specific species can be challenging Computer Graphics 15-462 24 Algorithmic Botany ã http://algorithmicbotany.org/papers/ ã Free 200pg ebook ã Covers many variants of L-Systems, formal derivations, and exhaustive coverage of different plant types Computer Graphics 15-462 25 PovTree Computer Graphics 15-462 26 Interactive Design With PovTree ã http://propro.ru/go/Wshop/povtree/povtree.html ã http://arbaro.sourceforge.net/ Computer Graphics 15-462 27 SpeedTree ã Fast procedural foliage is important for real-time applications ã http://www.speedtree.com/ Computer Graphics 15-462 28 L-Systems for Cities [Parish01] ã Start with a single street ã Branch & extend w/ parametric L-System ã Parameters of the string are tweaked by goals/constraints ã Goals control street direction, spacing ã Contraints allow for parks, bridges, road loops Computer Graphics 15-462 29 L-Systems for Cities (2) ã Once we have streets, we can form buildings with another L-System ã Building shapes are represented as CSG operations on simple shapes Computer Graphics 15-462 30 Procedural Hair [Chang02] ã Generate a model with a few hundred guide hairs ã Each hair is a rigid chain w/ revolute joints ã Use breakable springs between nearby hairs to simulate hairstyles ã Create triangle strips between adjacent hairs to simulate collisions ã Interpolate between guide hairs to produce many other hairs Computer Graphics 15-462 31 Procedural Hair (Examples) QuickTime™ and a H.263 decompressor are needed to see this picture. Computer Graphics 15-462 32 MojoWorld ã Commercial application for creating photorealistic procedural planets ã http://www.pandromeda.com/ Computer Graphics 15-462 33 Procedural Planets E. DeGuili Computer Graphics 15-462 34 Procedural Planets R. Fry Computer Graphics 15-462 35 Procedural Planets Y. Dinda Computer Graphics 15-462 36 Procedural Planets F.K. Musgrave Computer Graphics 15-462 37 Texturing and Modeling: A Procedural Approach ã D.S. Ebert et al ã 3rd Ed, 2003 ã Excellent reference ã http://www.mkp.com/tm3 ã http://www.texturingandmodeling.com/ Computer Graphics 15-462 38 Procedural Animation ã Particle Systems ã Ragdoll Physics ã Fluid simulation ã Flocking/crowd simulations Computer Graphics 15-462 39 Procedural Flocking (Boids) ã Simulate the movement of a flock of birds in 3-space ã Separation: move to avoid crowding local neighbors ã Alignment: steer towards average heading of neighbors ã Cohesion: steer towards average position of neighbors ã Limited Senses: only neighbors in forward-facing arc are observable Computer Graphics 15-462 40 Boids Example ã Open example Computer Graphics 15-462 41 Flow-Based Video Synthesis And Editing [Bhat04] ã Allows animator to easily create loops and variants of flowing natural phenomena (water,smoke,etc) ã Artist draws a set of flow lines on the original image ã Algorithm computes textures for a particle system that uses these flow lines ã Sequence of textures is transformed to prevent linear discontinuities ã Artist can then draw additional flow lines to create new variants Computer Graphics 15-462 42 Flow-Based Synthesis (Example) QuickTime™ and a decompressor are needed to see this picture. Computer Graphics 15-462 43 Flow-Based Synthesis (Example) QuickTime™ and a decompressor are needed to see this picture. Computer Graphics 15-462 44 Procedural Content: Games ã Reduces cost of art assets – Current AAA title costs upwards of $10M ã Reduces download/storage size ã Reduces memory throughput to GPU ã Provides enhanced replayability Computer Graphics 15-462 45 Games: Rogue-like ã All level layouts are procedurally generated ã Inspired games like Diablo, .hack, etc. Computer Graphics 15-462 46 Games: .kkrieger ã Demoscene FPS game ã Total file size: 97,280 bytes Computer Graphics 15-462 47 Games: Spore ã Multiple sub-games of creature/civilization gameplay ã Editors for creatures,buildings,vehicles ã Procedural behavior, animation, and texturing (driven by player- created models) Computer Graphics 15-462 48 Spore E3 2006 Video ã Show video Computer Graphics 15-462 49 Announcements Programming Assignment 4 is out No Class Thursday (Office Hrs On Request) Computer Graphics 15-462 50
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