1. CGMB214: Introduction to Computer Graphics
Topic 8
Interactive Input Methods & Graphical User Input

2. Objectives Explain the 6 logical classifications of input devices
Differentiate the 7 interactive Picture
Construction Techniques

3. Graphical Input Data
Types of input data: coordinate positions, attribute values, character-string specifications, geometric-transformation values, viewing conditions, illumination parameters,
Input procedures require interaction with display window managers & hardware devices.

4. Logical Classification of Input Devices
Logical input device refers to input devices classified according to data type.
LOCATOR – specifies one coordinate position
STROKE – specifies a set of coordinate positions
STRING – specifies text input
VALUATOR – specifies a scalar value
CHOICE – specifies menu selection
PICK – specifies picture component selection

5. Locator Devices
Devices like mouse, joystick,trackball, are used for screen-cursor position
General purpose keyboards may have 4 or 8 cursor-control keys
Light pen used for interactive input of coordinate position

6. Stroke Devices
Graphic tablet & continuous movement of mouse, trackball, joystick are used to input a sequence of coordinate positions

7. String Devices Primary physical device for string input is keyboard
Other devices could generate character patterns that is recognized using stored dictionary of predefined patterns for specific application

8. Valuator Devices
Valuator input is used to set scalar values for geometric transformations, viewing parameters & illumination parameters
Panel of controls dials typically provides valuator input
Display graphical representation of slider, buttons, rotating scales, menus
Joystick, trackball & keyboard could be adapted for valuator input by movement of the device relative to a scalar range

9. Choice Devices
Menus are used to select processing options, parameter values & object shapes
Touch panel, keyboard & voice entry are also common choice devices

10. Pick Devices
Used to select part of a scene that is to be transformed or edited
Using mouse, joystick or keyboard, picking the position of screen cursor to identify pixel coordinates
Depending on type of object & complexity of scene, several levels of search required to identify pick object

11. Interactive Picture Construction Techniques
Variety of interactive methods are incorporated into graphic package as aids in construction of pictures:
Basic Positioning Methods
interactively choose a coordinate position with a pointing device that records the screen location
Dragging
select an object & drag it to a new location, thus object is then displayed in the new location.
Constraints
procedure for altering input coordinate values to obtain a particular orientation or alignment of an object
lines are constrained to have a particular slant
Input coordinates are constrained to lie along predefined paths

12. Interactive Picture Construction Techniques
Grids
rectangular grid displayed on screen area used to round input coordinates to nearest grid intersection
grids facilitate object construction when need to joins new line to an existing line endpoint.
Rubber-Band Methods
Line segments & other basic shapes constructed & positioned using rubber-band methods to be interactively stretched or contracted

13. Interactive Picture Construction Techniques
Gravity Field
to connect lines at positions between endpoints (that are not in grid intersections) graphic packages include procedure to convert any input position near a line segment into a position on the line using gravity field area around the line
any selected position within the gravity field of a line is “moved” to the nearest position on the line
Interactive Painting & Drawing Methods
freehand drawing uses curves generated by following the path of a stylus on a graphics tablet or path of the screen cursor on a video monitor

14. Designing a Graphical User Interface
Applications include GUIs composed of display windows, icons, menus, etc to aid user in applying the software to a particular problem
Consideration for user interface area:
User Dialogue
Windows & Icons
Accommodating Multiple Skills Levels
Consistency
Minimizing Memorizing
Backup & Error Handling
Feedback