CS488 - Introduction to Computer Graphics - Lecture 2
Comments and Questions
- Combination to graphics lab.
- Location of TAs: DC2303.
- Class cancelled: March 11, 2008.
Output Devices
Main device from the beginning (1970s) was the colour cathode ray tube
(CRT).
CRT
Main components
- Electron beam
- Focussing and acceleration electrodes
- Beam steering electrodes
- Phosphor
Operational principle -- Persistence of vision
- Visual persistence time: 30 milliseconds.
- Television - 30 frames per second
- Movies - 24 frames per second
Types of CRT
- Vector, aka calligraphic
- Raster -- operational principle
- Finite resolution of vision
- 30 cycles per degree
- 60 pixels per degree, aka 3600 pixels per radian
- at 72 cm viewing distance, 5 pixels per millimeter
- Scan pattern
- Getting pixels out of memory
- Colour raster -- operational principles
- Three colour primaries ==> three frame buffers
- Shadowmask technology
Benefits of CRT
- Very inexpensive
- Good resolution
- Easy colour calibration
- High contrast
- Good field of view
- Comet-free motion
- Adjustable focus
Drawbacks of CRT
- Heavy and big
- Power hungry
- High voltage
- Dim
LCD
Key components
- Back light
- Programmable filters -- one per colour primary per pixel
- Each filter a cell of analogue (!!) DRAM
- with liquid crystal (LC) between the plates of the capacitor
- LC rotates polarization depending on the electric field
- polarization-selective filters do the rest
Advantages
- small
- light
- not as power hungry as CRT
Disadvantages - most of these are back light problems
- directional view
- back light consumes power
- not very bright
- poor extinction
- hard to calibrate colour
Others of the past
- Plasma displays
- LC projectors
Others of the future
Output Abstraction
- Array of addressable pixels
- Randomly addressable, thanks to the frame buffer
Input Devices
Two types of device
- Text input devices
- Pointing devices
Device input modes
- Request
- Normally used for text input
- Sample
- Fast, because OS-free
- Everything bad, because OS-free
- OS-mediated sampling
- Event
- Good programming abstractions
Modes can operate differently at hardware and software levels.
Input Abstraction
Event-based programming
- Event loop
- Callbacks
- abstrtacted into toolkits
- check example in 4.6.
Events can be as simple or elaborate as you like
Extra Layer of Output Abstraction
Return to: