Graphics Systems

• Most modern graphics systems
  • Input devices
  • CPU
  • GPU - Graphics Processing Unit
  • Memory
  • Frame Buffer
  • Output Devices
• Note the separation of I/O devices
• We pull the GPU out,
• And frame buffer probably never shown up before.
• Look at the picture on the bottom of page 5.
• Pixel stands for picture element.
• It is a a single "square" (we hope) in a display
• Pixels come from early output devices.
  • A raster is a two dimensional array of pixels.
  • In the end, this is what MOST output devices are capable of displaying.
  • A chunk of memory, in which the individual pixels are stored is called a frame buffer.
  • The frame buffer contains information such as
    • Pixel color
    • Current pixel depth
  • The size of the frame buffer is determined by
    • The number of pixels (width x height)
    • The information stored at each pixel
      • The depth - perhaps an int
      • Color - perhaps an int (or a short x 3 or 4)
  • As memory has become less expensive, frame buffers have changed over the years.
  • But the basic idea remains the same.
• In the past the CPU has been responsible for most Processing
• Currently GPSs have taken over much of this responsibility.
  • Graphics primitives such as lines, circles, polygons, ... are specified
  • Some entity converts from the primitive to a series of pixels.
  • This is called rasterization or scan conversion
  • These converted values are written to the frame buffer.
• Output Devices
  • The nearly extinct CRT - Cathode-ray tube.
    • Screen coated with phosphor
    • A beam of electrons strikes the screen causing it to glow for a period.
    • There are electronics to control where the beam is striking the screen.
    • There are electronics which control if the beam is on or not.
  • The refresh rate is the time it takes cover the entire screen. (30-120 times per second)
  • This combined with the frame buffer should provide a clue how monochrome images are displayed.
  • Grey scale displays
  • Color displays
  • Plasma Displays, LCD, ...
  • Most printers
  • A different beast: Plotters
    • Have a physical pen that moves by a robot arm.
    • Better to deal with vector graphics.
    • Work like we do.
• Input Devices
  • Two basic categories, plus new things.
    • Keystroke and button press devices
    • Pointing devices
  • For keystroke, and button press devices,
    • we are informed when the state of the buttons have changed.
    • Sometimes this is "the X button has been pressed"
    • Sometimes this is
      • button press
      • Button release
    • The operating system will buffer these for us (usually)
  • For pointing devices
    • Mostly we get changes in position.
    • Look at the mouse.
    • A mouse reports changes in two dimensions.
    • My space mouse reports changes in six dimensions. (or degrees of freedom)
    • These are both relative positioning devices.
    • A joystick, or even a steering wheel work the same way.
  • Devices like data tablets and touch screens are the exception
    • These are absolute positioning devices.
  • But most systems provide a layer between the raw devices (or even the raw devices as they appear to the os) and the programmer
  • Logical devices
    • This layer allows programs to be developed independent of the device.
    • For any device, we generally only get information when a action occurs within our area of the screen.
    • Frequently we get coordinates relative to our location on the screen.
• Three modes for input devices
  • Request mode - the way you write programs in 130/230/330 ...
  • Sample mode - Ask the device for the current state.
  • Event mode - when the device changes, an event is sent to your program