CG

• Logical classification of input devices

  Any device that is used to provide the specified data is referred to as a logical input device for that data type
• Standard logical input-data classifications

  • LOCATOR: A device for specifying one coordinate position
  • STROKE: A device for specifying a set of coordinate positions
  • STRING: A device for specifying text input
  • VALUATOR: A device for specifying a scalar value
  • CHOICE: A device for selecting a menu option
  • PICK: A device for selecting a component of a picture

  
• Locator devices


  • Interactive selection of a coordinate point is usually accomplished by positioning the screen cursor at some location in a displayed scene
  • Mouse, touchpad, joystick, trackball, spaceball, thumbwheel, dial, hand cursor, or digitizer stylus can be used for screen-cursor positioning
  • Keyboards are used for locator input in several ways
• Stroke devices


  • Used to input a sequence of coordinate positions
  • Continuous movement of a mouse, trackball, joystick, or hand cursor is translated into a series of input coordinate values
  • Graphics tablet is one of the more common stroke devices
• String devices


  • The primary physical device used for string input is the keyboard
  • Individual characters can be sketched on the screen using a stroke or locator-type device, and a pattern recognition program then interprets the characters using a stored dictionary of predefined patterns
• Valuator devices


  • Used to set scalar values for geometric transformations, viewing parameters, and illumination parameters
  • Typical physical devices are panel of control dials, slide potentiometers, joysticks, trackballs, tablets, and graphical representations of sliders, buttons, rotating scales, and menus
• Choice devices


  • Menus are typically used to select processing options, parameter values, and object shapes
  • Commonly used choice devices are cursor-positioning devices, keyboard function keys, and separate button boxes
  • Screen selection of menu options is done by comparing cursor position to menu item coordinates
• Pick devices


  • Used to select a part of a scene that is to be transformed or edited
  • Most often, pick operations are performed by positioning the screen cursor
  • Other pick methods include highlighting schemes, selecting objects by name, or a combination of methods
• Input modes


  Request mode: program initiates data entry, processing is suspended until required values are received<|>Sample mode: program and input devices operate independently, new values replace previously input data<|>Event mode: input devices initiate data input to the program, all input data is saved in a queue
• Echo feedback


  • Displaying information about input data and parameters, such as size of pick window, minimum pick distance, cursor type, highlighting, valuator input range and resolution
• Callback functions


  Specify what actions are to be taken by a program when an input event occurs, such as moving a mouse, pressing a mouse button, or pressing a keyboard key
• Echo feedback


  Includes:

  • The size of the pick window
  • The minimum pick distance
  • The type and size of a cursor
  • The type of highlighting to be employed during pick operations
  • The range (minimum and maximum) for valuator input
  • The resolution (scale) for valuator input
• Callback Functions


  For device-independent graphics packages, a limited set of input functions can be provided in an auxiliary library. Input procedures can then be handled as callback functions that interact with the system software. These functions specify what actions are to be taken by a program when an input event occurs. Typical input events are moving a mouse, pressing a mouse button, or pressing a key on the keyboard.
• Interactive Picture-Construction Techniques


  1. Basic Positioning Methods

  2. Dragging

  3. Constraints

  4. Grids

  5. Rubber-Band Methods

  6. Gravity Field

  7. Interactive Painting and Drawing Methods
• Basic Positioning Methods


  • We can interactively choose a coordinate position with a pointing device that records a screen location. How the position is used depends on the selected processing option. The coordinate location could be an endpoint position for a new line segment, or it could be used to position some object—for instance, the selected screen location could reference a new position for the center of a sphere; or the location could be used to specify the position for a text string, which could begin at that location or it could be centered on that location. As an additional positioning aid, numeric values for selected positions can be echoed on the screen. With the echoed coordinate values as a guide, a user could make small interactive adjustments in the coordinate values using dials, arrow keys, or other devices.