The problem with btKinematicCharacterController is that it doesn't take advantage of bullet's MotionState interpolation system. When you run your physics with fixed timestep, occasionally it can miss a frame, and the result is visible stutter. In my case I was using SDL's built-in timer, which reports time with a millisecond resolution and for 60 FPS it will report 16 or 17. Which means a slight desync between bullet's internal time and my vsync-based time. The solution is rather simple - keep previous character position and interpolate between it and the current one manually. The code is rather minimal. First we need a btKinematicCharacterController hack that keeps the previous, current positions and bullet's local time (the code is C++11):
Code:
class MyCharacterController : public btKinematicCharacterController {public: float local_time {0.0f}; Vec3 prev_pos; Vec3 cur_pos; MyCharacterController(btPairCachingGhostObject *ghost, btConvexShape *shape, btScalar step): btKinematicCharacterController(ghost, shape, step) {} void updateAction(btCollisionWorld *world, btScalar delta) override { btKinematicCharacterController::updateAction(world, delta); local_time += delta; prev_pos = cur_pos; cur_pos = ToVec3(m_ghostObject->getWorldTransform().getOrigin()); }};Code:
void Update(float delta) { btworld->stepSimulation(delta, 10); // will run character's updateAction zero or more times if (player->local_time > local_time) { // here we simply reset the time if we can, to avoid floating point precision issues player->local_time -= local_time; local_time = 0.0f; } local_time += delta; // this local_time is vsync-based time float diff = 1.0f - (local_time - player->local_time) / (1.f / 60.f); // 'player' is our MyCharacterController camera.position = player->prev_pos * diff + player->cur_pos * (1.0f - diff);}Also I would like to add a couple of things. If you do collision detection using a ray that starts from a camera - use the actual ghost object's position instead of interpolated one. Another thing that is worth mentioning is that you don't have to lag/interpolate the camera's orientation.
I hope it's useful for somebody at least.
Statistics: Posted by nsf — Thu Oct 24, 2013 5:55 pm
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