Graphics

1
Graphics

• not part of C
• libraries
• X libraries
• QT library
• OS specific

2
Introduction to Graphics

• Most commercial computer programs have graphical
  components
• A picture or drawing must be digitized for
  storage on a computer
• A picture is broken down into pixels, and each
  pixel is stored separately

3
Representing Color

• A black and white picture can be stored using one
  bit per pixel (0 white and 1 black)
• A color picture requires more information, and
  there are several techniques for representing a
  particular color
• For example, every color can be represented as a
  mixture of the three primary colors Red, Green,
  and Blue

4
Display

• Think of your display as a 2D array of pixels,
  each of which can be any of some (potentially
  large) number of colors
• for a solid background, make all the pixels one
  color
• to draw a line, change the color of all the
  pixels along the line
• for text, use a matrix of dots for each letter

5
Coordinate Systems
112

• Each pixel can be identified using a
  two-dimensional coordinate system
• commonly use a coordinate system with the origin
  in the upper left corner

40
(112, 40)
6
Graphical User Interface

• GUI
• window-based applications
• graphical components that the user can use to
  interact with the program
• menus
• buttons
• typically respond to mouse operations

7
GUI vs console applications

• graphical
• order of operations chosen by user

• text-based
• program flow designed into program

8
What GUI apps need

• graphical instead of text display
• respond to mouse and keyboard (including
  non-ascii keys, key combinations)
• components with standard behavior

9
Typical GUI Application

• Create a window
• Display the window
• Identify inputs to watch for
• Process user requests (events)
• mouse clicks
• key press
• window changes

10
GUI Application

• typically an infinite loop
• do
• wait for an event
• process event
• until program exits

11
Event Processing

• wait for an event
• identify source of event
• mouse, keyboard,
• take appropriate action
• actions often defined in functions

12
Libraries

• Primitive graphics operations are tedious
• keeping track of multiple objects can be very
  complex
• GUI interactions have to be done carefully if
  they are to work properly

13
Windowing Protocols

• X Windows - multi-platform, commonly Unix
• Mac OS
• Microsoft Windows
• it did not come first
• Each has a slightly different behavior

14
X Windows

• network-transparent GUI for workstations
• no difference between local and remote processes
• device-independent protocol for programming and
  using
• display-dependent implementation of the primitive
  graphics operations
• comes with most Unix systems

15
Xlib

• Library (C) of functions to do the graphics
  needed for X applications
• Higher level libraries for common interface
  components (windows, buttons, )
• Athena
• Motif
• QT

16
Programming X

• Tutorials
• http//www.kerguelen.org/x/index.html
• http//www.cs.uregina.ca/cdshaw/X11/x11notes.html
  
• http//www.comp.lancs.ac.uk/computing/users/sean/M
  otif-Workshop/workshop1.html
• Links to X Windows information
• http//www.rahul.net/kenton/xsites.framed.html

17
QT Library

• Commercially available for most OS
• http//www.trolltech.com/products/qt/index.html
• Documentation and tutorials on emerald
• /usr/lib/qt-2.3.0

18
Compiler options

• -L/pathToTheLibrary
• -lnameOfLib
• -I/pathToTheIncludeFiles