1. Lecture 3
OpenGL

2. Lecture 3 Review Rasterization OpenGL Libraries: GL, GLU, GLUT
Buffers:
Buffer Types
Clearing Buffers
Primitives
Colors
Sample Code

3. Lecture Three Color Modes Event Driven Programming
RGB vs. Color-Index mode
Event Driven Programming
Call back Registration
Mouse, Keyboard call backs
Reshape, Display, Idle
Double buffering
Animation

4. Color Modes RGB Mode: A color is specified by:
Red
Green
Blue
Alpha
Number of colors simultaneously displayed:
n bits represents 2^n colors.
8 to 16 bits represent 256 to 64K colors

5. Color Modes Color Index Mode: Uses Color Index Table
We can still use only 2^n color simultaneously
But the set of 2^n colors are picked from a table, Color Index Table
Void glutInitDisplayMode (GLUT_RGBA or GLUT_INDEX)

6. Choosing Color Model In order to choose a color Model use:
Void glutInitDisplayMode (GLUT_RGBA or GLUT_INDEX)
Need more details?
Visit ‘Online Resources’ in course website, or click following link

7. Event Driven Programming
Definition. A programming where the primary activity is reaction to the receipt of event.
Applications: GUI, HCI
Ingredients:
Events: Can be from any source, human input, e.g. mouse or other sensors.
Event Dispatcher: Assigns events to event handlers.
Event Handler

8. Event Processing in GLUT
Initial Setup:
Initializing Display Modes, e.g. Color mode, Single/Double Buffer, etc.
Entering GLUT event processing loop
void glutMainLoop (void)

9. Call Back Registration
Definitions:
current window
Normal Plane
Assigning events to event-handler.
glutReshapeFunction
glutDisplayFunction
glutKeyboardFunction
glutMouseFunction

10. Display Function The display function of current window
When is it called?
If the normal plane of a window needs to be redisplayed as a result of window damage. GLUT determines this based on redisplay state of a window.
When a user requests.
How is it called?
Implicitly: By GLUT, e.g. when the window system reports a region of the window's normal plane is undefined (for example, damaged by another window moving or being initially shown)
Explicitly: Using glutPostRedisplay function.

11. Reshape Function Takes care of Window Resize When is it called?
Whenever current window is reshaped
How is it called?
By GLUT
Width and height of new window is passed
void reshape (int w, int h)

12. main method GLUT initialization Registering Event Handler functions
glutInit (&argc, argv)
glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB)
glutInitWindowSize (width, height)
glutInitWindowPosition (X, Y)
Registering Event Handler functions
Display Function, Reshape Function, etc.
Entering GLUT Event Processing
glutMainLoop function

13. Sample Code in main method
glutInit(&argc, argv);
glutInitDisplayMode (GLUT_SINGLE | GLUT_RGB);
glutInitWindowSize (250, 250);
glutInitWindowPosition (100, 100);
glutCreateWindow (argv[0]);
glClearColor (0.0, 0.0, 0.0, 0.0);
glShadeModel (GL_FLAT);
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutMouseFunc(mouse);
glutKeyboardFunc(keyboard);
glutMainLoop();
return 0;

14. Event Handling: Keyboard
Registration
void glutKeyboardFunc (void (*func) (unsigned char key, int x, int y))
X,Y are the coordinate of mouse when key is pressed
Refer to online resources GLUT API for details about key callbacks.
For non-ASCII key strokes
F1~F12, Direction, Del, Ins, PgUp, etc.
glutSpecialFunc

15. Event Handling: Mouse Registration
void glutMouseFunc (void (*func) (int button, int state, int x, int y))
Button value:
GLUT_LEFT_BUTTON, GLUT_MIDDLE_BUTTON, or GLUT_RIGHT_BUTTON.
State Value:
GLUT_UP or GLUT_DOWN: Represents that the event happened because of press or release.
void glutMotionFunc (void (*func) (int x, int y))
Is called whenever the mouse moves within the window while one or more mouse buttons are pressed.
void glutPassiveMotionFunc (void (*func) (int x, int y))
Is called whenever the mouse moves within the window while no mouse buttons are pressed.

16. Idle Function Even sitting Idle is an event Handling Idle event
glutIdleFunc (void (*func) (void))
Most useful for creating animations

17. Example
Download the “Keyboard Event” sample code from the course website.
Let’s explain the code
Add an arbitrary mouse event to the code

18. Double Buffering Using Two buffers Is specified in initialization step
Front Buffer
Back Buffer
Is specified in initialization step
glutInitDisplayMode (GLUT_DOUBLE)
Replace glFlush() with glSwapBuffers()
Increases the performance
It’s NOT free, you have to pay: memory

19. Example
Download the “Double Buffer Example” sample code from the course website.
Compare the performance of Single buffer and Double buffer
Try to add events to the program.

20. Animation Algorithm Initialize GLUT windowing system
Initialize Event Handlers
Display
Reshape
Mouse, Keyboard, etc
Idle
Single/Double Buffering
glFlush or glSwapBuffers

21. Conclusion What we covered today: Color Modes Event Driven Programming
Registering Callback Functions
Double Buffering
Animation

22. QUESTIONS?

23. Next Week Basic 3D Graphics Basic Camera Setup and Control
Orthographic Projection
Perspective Projection
Drawing 3D Objects
GLUT solid and wireframe objects

24. END