Box2D Forums

Hi all.
I'm building some stuff with Qt and Box2D. I just follow the Hello Box2D with some of my customization, here is the screen:

The application hase the timer, each time the timer tick , I call world->Step(B2_TIMESTEP, B2_VELOCITY_ITERATIONS, B2_POSITION_ITERATIONS);

I get some trouble with set the value for TIMER_INTERVAL and B2_TIMESTEP.
About: B2_TIMESTEP, if I increase it let say 1000 times the movement of the green-box is different. When B2_TIMESTEP = 1.0f / 60.0f the small box jump out of the second ground-box, and when B2_TIMESTEP = 1000.0f / 60.0f the green-box land on the second ground-box. Why?

I think TIMER_INTERVAL around 16-20 is ok, right?
Thanks for your time.

The timeStep argument you supply to the Step function uses seconds as a unit (most values in Box2D use meters, kilograms, seconds, or radians for units). The timeStep value basically tells Box2D how long a single "frame" in your application is, and it should not vary as your program runs.

16-17 milliseconds is roughly 1/60th of a second (60Hz), which is appropriate. 60Hz is a typical frame rate.

Note that I don't know much about Qt, but there's a possibility that its timer does not have a very good resolution, which may make the Box2D simulation appear jittery. But it is my understanding that timing and timer APIs is outside of the scope of the Box2D library, so I'm not sure if you can get help with that here.

Hope I've been of help!