1/28/2000 CS 4/57101 Lecture 3 1

Development of Computer Graphics

z Early display devices:z Vector, stroke, line drawing, calligraphic displaysz Architecture of Vector Display

1/28/2000 CS 4/57101 Lecture 3 2

Development of Computer Graphics

z Architecture of a vector display - random scany vector generator converts digital coordinates to beam

deflections

1/28/2000 CS 4/57101 Lecture 3 3

Development of Computer Graphics

z Architecture of a raster display

1/28/2000 CS 4/57101 Lecture 3 4

Development of Computer Graphics

z Architecture of a raster display - raster scany beams (3 beams) intensity set to reflect pixel intensityy scan speed: originally 30Hz now 60Hz

1/28/2000 CS 4/57101 Lecture 3 5

Development of Computer Graphics

z Raster Scany need to store whole imagey 1024 x1024 x n - n bits per pixely mono 1 bit, color 8 (256 color), 24 (16 million)y 32 to 96 bits used (double buffering, z-buffering)y 1280x1024x24 needs only 3.75 MB video RAM

1/28/2000 CS 4/57101 Lecture 3 6

Development of Computer Graphics

z Random Scan versus Raster Scany note ragged lines

1/28/2000 CS 4/57101 Lecture 3 7

Development of Computer Graphics

z Random Scan versus Raster Scanz Raster advantages:

y low cost, superior fill ability, refresh rate independent ofcomplexity

z Raster disadvantages:y discrete nature of pixel representation, need for scan conversion

in software or RIP chipsy real-time dynamics more demandingy approximation of lines by pixels

x aliasing - jaggies or staircasingx manifestation of sampling error in signal processingx need for anti-aliasing

1/28/2000 CS 4/57101 Lecture 3 8

Development of Computer Graphics

z Input Devicesy early light pens to modern micey data tablety touch sensitive screensy 3D input devices (spaceballs etc.)y button and dial boxes

1/28/2000 CS 4/57101 Lecture 3 9

Describing Scene to be viewed

z Application Program - creates applicationz Application Model - independent of display system

y program must extract geometry and convert to primitives ofgraphics system

y primitives: points, lines, (rectangles, ellipses, text, polygons,polyhedra, spheres, curves, surfaces

y application must convert geometry to primitives supportedy attributes (line style, color, line width, fill style)

1/28/2000 CS 4/57101 Lecture 3 10

Graphics Systems

z Typically libraries: output subroutinesy user program in logical display device termsy graphics library converts to device dependent instructionsy abstraction of display device

x locator - mouse, tablet, joystick etcx sample - return from locatorx event - generated by user input

1/28/2000 CS 4/57101 Lecture 3 11

z Interaction Handling - event driven loopy while (!quit) {

x enable selection of commands/objectsx wait for user selectionx switch (selection) { process selection, updating model and

screen as necessary}y }

z User interactiony change in screen appearance - does not involve update of

model: application updates state and calls graphics packagey change in model : must recalculate

Graphics Systems