development of computer graphicsfarrell/cg00/lectures/cg03.pdf · z random scan versus raster scan...
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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
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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