Animation is created by rapidly displaying a sequence of images to create the illusion of movement. There are two main methods for automated animation updates in a window: the idle callback, which is invoked when no other events are happening, and the timer callback, which is invoked after a specified time period. A simple line animation example is provided using single buffer rendering, but it is hardware dependent and inconsistently speeds up and slows down. Using double buffering and a timer callback that redraws and reschedules itself every 30 milliseconds results in a smoother animated line.

1. Presented By: Kiran Munir 08-SE-59

2. Animation is the rapid display of a sequence of images of 2-D or 3-D artwork or model positions in order to create an illusion of movement. "Animation" would be the technique of giving "soul" to objects and drawings

3. For animation We can explicitly force the display callback to be invoked by issuing the command glutPostRedisplay() .

4. For automated simulation We need a mechanism for the window to be continually updated automatically. Idle Callback ( glutIdleFunc() ) Timer Callback ( glutTimerFunc() ).

5. The Idle Callback specifies a function that is invoked whenever the system is not handling any other callbacks or events. Timer Callback specifies a function that is invoked after a specified time period.

6. A Simple Animation

8. float X=0.0; float deltaX=0.01;

9. Void draw(void) { glClear (GL_COLOR_BUFFER_BIT); glBegin (GL_LINES); glVertex3f ( X, 0.25,0.0); glVertex3f ( 1.0-X , 0.75,0.0); glEnd ( ); glFlush (); X+=deltaX; if(X>=1.0 || X<=0.0){ deltaX=-deltaX; } glutPostRedisplay(); }

11. Single Buffer Rendering Hardware Dependence Inconsistent speed

12. A Smooth Animation

19. Now to compile and execute we see a smooth animated line segment Double buffering is insignificant In this case, but is important in drawing complex scenes.

20. No real solution Make faster computers slow Important for consistency

21. Animation Delay Select the minimal hardware configuration Set a time delay for animation

22. Glut Timed Callback GlutTimerFunc();

23. glutTimerFunc(time,function,arg) This causes function() to be called after time milliseconds with arg as an argument to function()

24. void Timer(int unused) { glutPostRedisplay(); glutTimerFunc(30,Timer,0); }

26. At the end of 30 milliseconds the function timer is called again and dispatches the redisplay and timer messages. To compile and execute the program we see a much smoother animation. Simultaneously running applications can slow down your animation.

28. http://xoax.net/ http://nehe.gamedev.net