CGMB214: Introduction to Computer Graphics

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