Introduction to Computer Graphics CS 445 / 645 David Brogan dbrogan@cs.virginia.edu

Administrivia Syllabus Instructor/TA coordinates Prereqs Texts Assignments Grading & Honor Code Topic list

Impact of Computers Moore’s Law Power of a CPU doubles every 18 months / 2 years

Impact of Video Games (Nvidia) Number of transistors on GPU doubles each 6 mos. Three times Moore’s Law Good article on Jen-Hsun Huang, Nvidia CEO: http://www.wired.com/wired/archive/10.07/Nvidia_pr.html Lee Majors Col. Steve Austin Worldwide revenues Retro flashback??? $7 Billion Man $5.6 Billion Man

Impact of Video Games But… Video game sales is roughly same as Hollywood boxoffice Americans bought $3.2 in VCRs and DVDs last yr Total revenues to movie studios is 5 times total video game revenues

Future of Consoles 33 million PS2s 3.9 million Xboxes MSFT still losing $89 per console Predicted 200 million PDA/Cell game players in 2005 Do you believe it?

Graphics Applications Entertainment: Cinema Square: Final Fantasy Pixar: Monster’s Inc.

Graphics Applications Medical Visualization The Visible Human Project MIT: Image-Guided Surgery Project

Graphics Applications Everyday Use Microsoft’s Whistler OS will use graphics seriously Graphics visualizations and debuggers Visualize complex software systems

Graphics Applications Scientific Visualization

Graphics Applications Computer Aided Design (CAD)

Graphics Applications Entertainment: Games GT Racer 3 Polyphony Digital: Gran Turismo 3, A Spec

The Basics Computer graphics: generating 2D images of a 3D world represented in a computer. Main tasks: modeling: (shape) creating and representing the geometry of objects in the 3D world rendering: (light, perspective) generating 2D images of the objects animation: (movement) describing how objects change in time

Why Study Computer Graphics? Graphics is cool I like to see what I’m doing I like to show people what I’m doing Graphics is interesting Involves simulation, AI, algorithms, architecture… I’ll never get an Oscar for my acting But maybe I’ll get one for my CG special effects Graphics is fun

Can we learn from history? Among the studies of natural causes and laws, it is light that most delights its students. Among all the great branches of mathematics, the certainty of its demonstrations pre-eminently elevates the minds of its investigators. Perspective, therefore, should be preferred above all man’s discourses and disciplines. In this subject the visual rays are elucidated by means and demonstrations which derive their glory nor only from mathematics but also from physics; the one is adorned equally with the flowers of the other. Leonardo da Vinci (1400’s) quoting John Pecham (1200’s)

Perspective

Machines

Leonardo Again There are some who look at the things produced by nature through glass, or other surfaces or transparent veils. They trace outlines on the surface of the transparent medium… But such an invention is to be condemned in those who do not know how to portray things without it, no how to reason about nature with their minds… They are always poor and mean in every invention and in the composition of narratives, which is the final aim of this science

Perspective Lorenzetti Birth of the Virgin 1342

Leonardo The Last Supper 1498

Shape

We Labor On… Light Stage – 2002 USC, Institute for Creative Technologies Note: Paul Debevec will visit UVa in October to talk about this and other cool things

Display Technologies Cathode Ray Tubes (CRTs) Most common display device today Evacuated glass bottle Extremely high voltage Heating element (filament) Electrons pulled towards anode focusing cylinder Vertical and horizontal deflection plates Beam strikes phosphor coating on front of tube

Electron Gun Contains a filament that, when heated, emits a stream of electrons Electrons are focused with an electromagnet into a sharp beam and directed to a specific point of the face of the picture tube The front surface of the picture tube is coated with small phospher dots When the beam hits a phospher dot it glows with a brightness proportional to the strength of the beam and how often it is excited by the beam

Display Technologies: CRTs Vector Displays Anybody remember Battlezone? Tempest?

Display Technologies: CRTs Vector Displays Early computer displays: basically an oscilloscope Control X,Y with vertical/horizontal plate voltage Often used intensity as Z Name two disadvantages Just does wireframe Complex scenes  visible flicker

Display Technologies: CRTs Raster Displays Raster: A rectangular array of points or dots Pixel: One dot or picture element of the raster Scan line: A row of pixels

Display Technologies: CRTs Raster Displays Black and white television: an oscilloscope with a fixed scan pattern: left to right, top to bottom To paint the screen, computer needs to synchronize with the scanning pattern of raster Solution: special memory to buffer image with scan- out synchronous to the raster. We call this the framebuffer.

Display Technologies: CRTs Phosphers Flourescence: Light emitted while the phospher is being struck by electrons Phospherescence: Light emitted once the electron beam is removed Persistence: The time from the removal of the excitation to the moment when phospherescence has decayed to 10% of the initial light output

Display Technologies: CRTs Raster Displays Frame must be “refreshed” to draw new images As new pixels are struck by electron beam, others are decaying Electron beam must hit all pixels frequently to eliminate flicker Critical fusion frequency Typically 60 times/sec Varies with intensity, individuals, phospher persistence, lighting...

Display Technologies: CRTs Raster Displays Interlaced Scanning Assume can only scan 30 times / second To reduce flicker, divide frame into two “fields” of odd and even lines 1/30 Sec 1/60 Sec Field 1 Field 2 Frame

Display Technologies: CRTs Raster Displays Scanning (left to right, top to bottom) Vertical Sync Pulse: Signals the start of the next field Vertical Retrace: Time needed to get from the bottom of the current field to the top of the next field Horizontal Sync Pulse: Signals the start of the new scan line Horizontal Retrace: The time needed to get from the end of the current scan line to the start of the next scan line

Display Technology: Color CRTs Color CRTs are much more complicated Requires manufacturing very precise geometry Uses a pattern of color phosphors on the screen: Why red, green, and blue phosphors? Delta electron gun arrangement In-line electron gun arrangement

Display Technology: Color CRTs Color CRTs have Three electron guns A metal shadow mask to differentiate the beams

Display Technology: Raster Raster CRT pros: Allows solids, not just wireframes Leverages low-cost CRT technology (i.e., TVs) Bright! Display emits light Cons: Requires screen-size memory array Discreet sampling (pixels) Practical limit on size (call it 40 inches) Bulky Finicky (convergence, warp, etc)