ch2

• Graphics Hardware


  • Raster Display Systems
  • Introduction to the 3D Graphics Pipeline
  • The Z Buffer for Hidden Surface Removal
• Video monitor


  The most common graphics display device
• Cathode Ray Tube (CRT)


  The most common technology for video monitors
• Operation of CRT


  1. Electron gun emits a beam of electrons

  2. Electron beam passes through focusing and deflection systems

  3. Beam hits the screen, phosphor emits light

  4. Redraws the picture by directing the electron beam back over the same screen points quickly
• Color display


  CRT devices have three electron beams, phosphor dots are in groups of three, relative brightness of red, green and blue components determines the color
• Random scan


  • Beam is only directed to areas of the screen where parts of the picture are to be drawn, draws a picture as a set of primitives like lines or curves
• Raster scan


  • Primitives to be drawn are first converted into a grid of dots, the brightness's of these dots are stored in a frame buffer, the electron beam sweeps across the screen line-by-line, visiting every location on the screen, but it is only switched on when the frame buffer indicates that a dot is to be displayed at that location
• Frame buffer


  A 2D array of data values, with each data value corresponding to a pixel in the image, the number of bits used to store the value for each pixel is known as the bit-planes or depth of the frame buffer
• Raster


  A grid of phosphor dots on the display screen, each row of pixels is known as a scan-line, the number of pixels in a scan-line is the x-resolution, the number of scan-lines is the y-resolution, the ratio of the y-resolution to the x-resolution is the aspect ratio
• Persistence


  The length of time that the phosphor emits light after the electron beam has moved on
• Refresh rate


  The number of times that the entire raster is refreshed (i.e. drawn) each second
• Interlaced scanning


  • Alternate scan-lines are updated in each raster refresh, effectively doubling the screen refresh rate to reduce flicker
• Common video formats


  • VGA: 640x480, 60 f/s, non-interlaced
  • PAL: 625x480, 25 f/s, interlaced
  • NTSC: 525x480, 30 f/s, interlaced
• Flat-panel displays


  A class of video devices that have reduced volume, weight, and power requirements compared to a CRT, can be emissive (e.g. plasma, LED) or non-emissive (e.g. LCD)
• 3D display using vibrating mirror

  CRT image is reflected from a vibrating, flexible mirror, the vibrations are synchronized with the display of an object so that each point on the object is reflected from the mirror into a spatial position corresponding to the distance of that point from a specified viewing location
• Stereoscopy


  The process of generating 3D displays by providing a stereo pair of images, one to each eye of the viewer, so that the viewer can perceive the depth of objects in the scene as well as their position
• Head-mounted displays (HMDs)


  • Displays that are mounted on the head of the viewer, providing separate images to the left and right eyes to produce a sense of stereo immersion
• Head-tracked displays (HTDs)


  • The display remains stationary, but the head of the viewer is tracked so that the images presented in the display can be updated
• Stereoscopy does not produce true 3D images, but it does provide a 3D effect by presenting a different view to each eye
• Display processor


  Contains dedicated hardware for drawing graphics primitives, also known as graphics controller, display coprocessor, graphics accelerator and video card
• Operation of display processor

  Interpreter or hardware that converts display processor code into analog values for the picture
• The main purpose of the display processor is to convert the digital information from the CPU to analog values for display
• HMD


  The display moves with the viewer's head
• HTD


  The display remains stationary, but the head of the viewer is tracked so that the images presented in the display can be updated
• Stereoscopy method does not produce true 3D images, but it does provide a 3D effect by presenting a different view to each eye of an observer so that scenes do appear to have depth
• CPU


  Most (non-graphics) processing will occur in the CPU of the computer, which uses the system bus to communicate with the system memory and peripheral devices
• Graphics routines


  Executed by the display processor, which contains dedicated hardware for drawing graphics primitives
• Names for the display processor

  • Graphics controller
  • Display coprocessor
  • Graphics accelerator
  • Video card
• Display Processor


  The interpreter or a hardware that converts display processor code into picture
• Main purpose of the Display Processor

  To free the CPU from most of the graphic chores
• Video controller


  A special-purpose processor used to control the operation of the display device
• Display controller


  The part of a computer's motherboard that handles outputting graphic images to a monitor or display
• Display-processor memory


  A separate memory area that can be provided in addition to the system memory
• Graphical input devices


  • Keyboards
  • Button boxes
  • Dials
  • Mouse
  • Trackballs
  • Space balls
  • Joysticks
  • Cursor-control keys
  • Thumbwheels
  • Data gloves
  • Image scanners
  • Digitizers
  • Touch panels
  • Light pens
  • Voice systems
• Hidden Surface


  When viewing a picture containing non-transparent (Visible) objects and surfaces, it is not possible to see those objects from view which are behind from the objects closer to the eye
• To get the realistic screen image, removal of these hidden surfaces is a must
• Hidden-surface problem


  The identification and removal of these surfaces
• Approaches for removing hidden surface problems

  • Object-Space method
  • Image-Space method
• Object-Space method


  Determine which part of the object is visible. Various parts of objects are compared to determine visible, invisible or hardly visible surfaces
• Image-Space method


  Determine per pixel which point of an object is visible. Each point is detected for its visibility. If a point is visible, then the pixel is on, otherwise off