Physics time-step function in Flick a' Fruit

gistfile1.j

- (void) step:(ccTime)elapsedTime
{   
    // Do physics time-stepping.
    _dtAccumulator += elapsedTime;

    while (_dtAccumulator >= _dt) {
        // Take the actual physics step with step-size _dt
        cpSpaceStep(_space, _dt);

        _dtAccumulator -= _dt;
    }

    // Note that accumulator will not be zero at the end of this, it will
    // most likely be < FIXED_TIMESTEP. This indicates that the Physics is
    // ahead of the rendered frame. To fix this, we need to interpolate
    // the sprites for each object between their previous positions (before the
    // timestep) and their current position based on the fractional value
    // stored in the accumulator. This is only for display purposes so that we
    // don't get temporal aliasing.
    float alpha = _dtAccumulator / _dt;


    // The following function will for each physical object, 
    // interpolate the position of the sprite based on:
    // previousPhysicsPosition * (1 - alpha) + currentPhysicsPosition * (alpha)
    cpSpaceEachBody(_space, interpolateSprites, &alpha);
}