Computer Graphics

Lecture 2 - Computer Hardware and Software


Video Display Devices

Cathode Ray Tube (CRT)



Vector Display

Random Scan display

Calligraphic Refresh Display

Direct-view Storage Tube Display


Raster Display





Flat Panel Displays



Each pixel made of three cells containing xenon and neon gas

Horizontal and vertical electrodes create unique grid to locate cell positions

Gas in each cell is ionized when a voltage difference is applied to intersecting electrodes

The current creates a rapid flow of charged particles, which stimulates the gas atoms to release photons of ultraviolet light

Photons excite the phosphor coated on the inside wall of the cell.



(Pictures from: "How Plasma Displays Work")





Organic molecules that align themselves in crystalline structures in the absence of external forces

Application of external force rearranges them as if they were a liquid

Liquid crystals respond to heat or electromagnetic forces


LCDs used as optical modulators

Change polarization

In unexcited or crystalline state, LCDs rotate the polarization of light by 90 degrees.

In the presence of an electric field, LCDs behave like a liquid and align their electrostatic charges with E field.





Augmented Display Systems

Virtual Reality

Definition - VR is a computer generated, interactive, three-dimensional environment in which a person is immersed.

  • This implies:
    • Requires a high performance computer graphics system to provide an adequate level of realism.
    • The virtual world is interactive. A user requires real-time response from the system to be able to interact with it in an effective manner.
    • The last point is that the user is immersed in this virtual environment. This usually means that the user wears a head mounted display.

Virtual Reality Interface Devices

HMD - head mounted display

  • Best known approach to VR
  • Coupled with head tracking
  • Stereo binocular view of the virtual world often with stereo audio
  • By virtue of tracking the viewing position (the head) and orientation in the physical world, the view and perspective of the virtual are consistent with what one would experience in the physical world from the same actions.
  • Permit some means of input, such as a dataglove or some other high degree of freedom input to  support interaction with the displayed virtual world.
  • stereo display, much like a pair of glasses that provides a view into the virtual world.
  • The physical form of these “glasses” can range from something on the scale of a motorcycle helmet to a pair of sunglasses
  • Great variety in display quality
  • Goal is to provide the widest field of view at the highest quality and with the least weight and at a reasonable cost.
  • Issues:
    • HMDs cover eyes
    • Virtual world seen at the expense of the physical.
    • Users cannot directly see:
      • their hands or the devices that they are controlling
      • objects or other people who are in their immediate physical environment
    • Solution:
      • Some representation of physical world entities must appear in the virtual
      • Mount one or more video cameras onto the HMD and feed the signals to the displays


Surround Environments

Cave based VR

  • User functions within a room on which one or more of the surfaces (walls, floor, ceiling …) is the display
  • Some or all of the walls of a room are rear-projection stereo displays
  • User wears glasses to enable viewing of stereo images
  • Since glasses are transparent, one can see the physical as well as the virtual world
  • Computer generated objects appear to enter into the physical space of the Cave itself, where the user can interact with them directly
  • User’s head position is tracked within the Cave so that what is displayed preserves proper perspective, etc., in adapting to movements and change of location of gaze
    • Issue:
      • Two people in cave - both are viewing the same displays, preventing each from own “point of view.”
      • Both viewers look at different things and different directions, but do so as if from the perspective of the current location of the head tracker.
  • Some mechanism for interacting with what is scene.

1992/93 - EVL's Cave ( )
Cruz-Neira, Sandin, DeFanti, Kenyon and Hart
Electronic Visualization Lab - University of Illinois at Chicago Circle

  • Generic Immersive VR Environment
  • A theater 10x10x9 feet, made up of three rear-projected screens for walls and a reflective projection for the floor.
  • High resolution, high bandwidth, short persistance CRT projectors throw full-color workstation fields (1024x768 stereo) onto the screens, giving approximately 3,000 linear pixel resolution to the surrounding composite image.
  • Computer-controlled audio provides a sonification capability to multiple speakers.
  • User's head and hand orientation and position are aquired using an Ascension tracking system with tethered electromagnetic sensors.
  • Stereographics' LCD stereo shutter glasses are used to separate the alternate fields going to the eyes.
  • SGI InfiniteReality Engine is used to create the imagery that is projected onto the walls and floor.

Trimension                             Cabin - Fully enclosed cave

Image Construction : 5 - 6 Cameras

Domes and Walls

SkyVision Full-Dome (

  • Sloping seats, zenith position.
  • Different projector orientations .


  • Primary goal is to fill peripheral vision.
  • 16:9 aspect ratio format


Personal Domes

Elumens Visionstation (VS) - Hemispherical Display       Elumens Visionstation (VS3)

Elumens Visionstation (VS3)
Depth: 8'-10" (106")
Height: 7'-9" (93")
Width: 11'-4" (136")

Partial Immersion

Panoramic - Curved Walls

  • Typically use RGB projectors (Varing focal depth)
  • Edge blending (On computer or with video hardware)
  • Small "sweet" spot.

Trimension (others - Barco)


  • How to synchronise multiple devices (Computer, DVD)
  • Multiple pipe graphics cards (Cost)
  • Seams between walls (Aligned, edge blending)
  • Front vs back projection (Space)

Three Wall  - CAEV -   Melbourne University      Two Wall - PortaWedge - Melbourne U.

Tables,  Desks, Single Screens

Immersadesk 2 - EVL

Fakespace                             Trimension


The Grip Project - UNC Chapel Hill - Molecular Visualization

The NanoManipulator - UNC Chapel Hill


Responsive Workbench - 1993

  • 3D interactive workspace originally developed by Wolfgang Krueger at GMD
  • Computer-generated stereoscopic images are projected onto a horizontal tabletop display surface via a projector-and-mirrors system, and viewed through shutter glasses to generate the 3D effect
  • A 6DOF tracking system tracks the user's head, so that the user sees the virtual environment from the correct point of view.
  • A pair of gloves and a stylus, also tracked by the system, can be used to interact with objects in the tabletop environment.


Low Cost Stereo Table - Pace University (CAM)


Cubby - Delft


Stereoscopic Displays

Mount Fuji Stereo Pairs
                                        Free Viewing                       Cross Eyed Viewing
                Left Eye                                      Right eye                                 Left Eye

  • Head Mounted Displays

5DT HMD 800
Display Resolution: 800x600x3(rgb) pixels - Full SVGA
Optics Field of View: 28 (H) x 21 (V) degrees
Type: Sennheiser HD 25 closed dynamic headphones
Frequency Responce: 16Hz - 22Hz (3dB)

  • Shutter Glasses (Active Stereo)

Crystal Eyes (Stereographics )


  • Polarized Glasses (Passive Stereo)


Autostereographic Display

Dresden 3D (also Stereographics and others) - 15" - 18"

MultiMo3D , Heinrich-Hertz-Institut für Nachrichtentechnik, Germany
Principles and prototype of a 50-inch projection-type dual lenticular screen 3D display.

Volumetric Display - Actuality Systems

Image Size and Display Type

- Approx. 10" diameter spherical image
- Swept-screen multiplanar volumetric display
- Autostereoscopic: no viewing goggles
- Volume-filling imagery
- Supports many simultaneous viewers – no head-tracking


Input Hardware

Tracker - Head position and Orientation
    - Determines viewpoint of virtual world

  • 5DT 3D-BIRD
    - tracking of orientation angles
    - move up, down, side to side, and rotate (yaw, pitch and roll)

Datagloves - Hand position and orientation
    - Monitors status of user's fingers

  • 5DT Data Glove 5 ( )
    Measures each finger flexure and the orientation (pitch and roll) of the user's hand


Haptics - Force Feedback



Other Input/Output Devices

Image Scanners

Printers (Raster)



Plotters (Vector)

3D Printing

Stereolithography (from )

Create a 3-D model of object

Software slices model into thin layers -- typically five to 10 layers/millimeter

The 3-D printer's laser "paints" one of the layers, exposing the liquid plastic in the tank and hardening it

The platform drops down into the tank a fraction of a millimeter and the laser paints the next layer

This process repeats, layer by layer, until your model is complete



                                                                                          Mpeg Movie of part


Ink-jet Printing – (e.g. Z-Corp )

    1. The 3D Printer spreads a thin layer of powder
    2. An ink-jet print head prints a binder in the cross-section of the part being created
    3. The build piston drops down, making room for the next layer, and the process is repeated
    4. Whenthe part is finished, it is surrounded and supported by loose powder, which is then shaken loose from the finished part.


Graphics Software

Languages -> Commands -> APIs

Coordinate Systems

Local Coordinates

World Coordinates

Device Coordinates


Model -> World -> Normalized -> Device

Graphics Functions

General purpose graphics packages provide:

Functions – I/O, attributes, transformations, viewing

Output primitives – building blocks of images

Attributes – properties of images

Geometric transforms

Viewing transforms

Software Standards:



OpenGL –

Web3D –