Change velocity at a particular point

I have created a body that moves in the windows of size 800,600
which moves with velocity(10,10). and that’s the init graphics function code
void InitGraphics(int argc, char *argv[]) {
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGBA | GLUT_DOUBLE);
glutInitWindowPosition(100, 100); //pass (-1, -1) for Window-Manager defaults
glutInitWindowSize(800, 800);
glutCreateWindow(“OpenGL Lab”);
body.P.Set(0, 0);



i want to change the velocity of the body to move in the o ppisite direction when it reach the point y=30

just check the offset of the body inside the function OnDisplay and change the velocity to the opposite direction when y = 30.

Make sure you call body.Update(0.01); inside OnDisplay as well (I assume this updates the position)