Lecture 3 OpenGL

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

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

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

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)

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 http://www.cse.yorku.ca/~alireza/courses/540/rgba.pdf

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

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)

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

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.

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)

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

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;

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

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.

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

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

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

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.

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

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

QUESTIONS?

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

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