CODEWITHSUNDEEP
copenglanimation
rofans91
rofans91

Reputation: 3010

How To Slow Down glutIdleFunc Animation Speed

Dear all I am trying to create animation using OpenGL through glutIdleFunc(). Below is my code:

float t = 0.0;

void idle (void)
{
    t += 0.1;
    if (t > 2*pi)  
    { 
        t = 0.0; 
    }
    glutPostRedisplay();
}

//in main function
glutIdleFunc(idle);

I have been trying to adjust the increment of t in order to slow down my animation. But somehow my animation keeps moving on too fast, until I can't catch it with my eye. Does anyone know how to slow down this kind of animation? Thank's

Upvotes: 1

Views: 4700

Answers (2)

Drew Hall
Drew Hall

Reputation: 29055

Rather than trying to find an artificial t value to use in your idle function, you'll probably be better off using a real timer such as C's time(). Then, simply advance your animation by the appropriate amount given the elapsed time since the last frame was drawn.

Here's how it might look:

time_t lastTime;

void draw() {
  const time_t now = time();
  const double dt_s = difftime(now, lastTime);

  // Update your frame based on the elapsed time.  For example, update an angle
  // based on a specified rotation rate (omega_deg_s):
  const double omega_deg_s = 10.0;
  angle += dt_s * omega_deg_s;
  angle = fmod(angle, 360.0);

  // Now draw something based on the new angle info:
  draw_my_scene(angle);

  // Record current time for next time:
  lastTime = now;
}

Upvotes: 2

Lexi
Lexi

Reputation: 1730

You need to use the time since the last function call rather than a straight value as your metric, since that time may vary.
For more information, read valkea's answer on GameDev, which suggests that you use glutGet(GLUT_ELAPSED_TIME) to calculate that value.

Upvotes: 2

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