View Full Version : Moving a circle across

12-26-2009, 11:10 AM
hi all.
I want to draw a circle on the push of a particular key and make it move across the screen. Heres the snippet:
This is the function to catch the key press:

void keyPressed(unsigned char key, int x, int y)
/* avoid thrashing this procedure */

/* If escape is pressed, kill everything. */
if (key == ESCAPE)
/* shut down our window */

/* exit the program...normal termination. */

if(key == 102 || key == 70)

And this is the function to draw the circle which is not registered as a display function:

void foo(){
glTranslatef(3.0f,0.0f,0.0f); // Move Right 3 Units

int j;
float x = 0.05f * cos(359 * PI/180.0f);
float y = 0.05f * sin(359 * PI/180.0f);
for(j = 0; j < 360; j++)
x = 0.05f * cos(j * PI/180.0f);
y = 0.05f * sin(j * PI/180.0f);


Now since the above function is not registered as a display function, it is not redrawn and i want it to be redrawn. The circle is displayed and disappears. Recursion is bit messy(in processing terms) and i am not looking at it now.

Any suggestions?
Thank you.

12-27-2009, 02:28 AM
I cant understand what you exactly want to do.

How do you expect the scene to be redrawn if it is not registered as a display callback?

If you want to see the circle drawn in steps I suggest the following:

- declare a static counter variable ( say i)
- iterate over i after every callback to foo();
- use a timer function glutTimerfunc(*timer_func,value,1); value = 30ms or whatever.
- and register your display func. That is necessary!
- Check if you have enabled Double buffering, otherwise when you swap buffers the result will be a blank screen as you mentioned.

hope this helped.