I'm trying to implement the https://gafferongames.com/post/fix_your_timestep article but I have jitter on the position interpolation.
I have the following PhysX manager class update method :
const float fixedTimeStep = 1.0f / 60.0f; // 60Hz float deltaTime = TimeManager::GetInstance()->DeltaTimeF(); if (deltaTime > 0.25f) deltaTime = 0.25f; accumulator += deltaTime; static std::unordered_map<PxRigidDynamic*, PhysXState> statesBefore{}; static std::unordered_map<PxRigidDynamic*, PhysXState> statesAfter{}; if (statesBefore.empty()) { RetrieveCurrentState(statesBefore); RetrieveCurrentState(statesAfter); } while (accumulator >= fixedTimeStep) { statesBefore = statesAfter; mScene->simulate(fixedTimeStep, nullptr, GSimulateScratchMemory, GSimulateScratchMemorySize); accumulator = std::max(accumulator - fixedTimeStep, 0.f); mScene->fetchResults(true); RetrieveCurrentState(statesAfter); } // Calculate the interpolation factor for rendering float alpha = accumulator / fixedTimeStep; for (const auto& [body, stateBefore] : statesBefore) { if (statesAfter.find(body) != statesAfter.end()) { const auto& stateAfter = statesAfter.at(body); PhysXState interpolatedState{}; InterpolateStates(stateBefore, stateAfter, alpha, interpolatedState); // Update the interpolated state in the body userptr moveable body auto userPtr = static_cast<CollisionParam*>(body->userData); if (userPtr && userPtr->Body) { userPtr->Body->SetInterpolatedState(interpolatedState); } } } This is how I retrieve the current state:
void RetrieveCurrentState(std::unordered_map<PxRigidDynamic*, PhysXState>& states) { states.clear(); for (auto rigidBody : mRigidBodies) { PhysXState state; physx::PxTransform transform = rigidBody->getGlobalPose(); state.Position = glm::vec3(transform.p.x, transform.p.y, transform.p.z); state.Orientation = glm::quat(transform.q.w, transform.q.x, transform.q.y, transform.q.z); physx::PxVec3 linearVelocity = rigidBody->getLinearVelocity(); state.Velocity = glm::vec3(linearVelocity.x, linearVelocity.y, linearVelocity.z); physx::PxVec3 angularVelocity = rigidBody->getAngularVelocity(); state.AngularVelocity = glm::vec3(angularVelocity.x, angularVelocity.y, angularVelocity.z); states[rigidBody] = state; } } And here is how I interpolate:
void InterpolateStates(const PhysXState& previous, const PhysXState& current, float alpha, PhysXState& interpolated) { interpolated.Position = glm::mix(previous.Position, current.Position, alpha); interpolated.Orientation = glm::slerp(previous.Orientation, current.Orientation, alpha); interpolated.Velocity = glm::mix(previous.Velocity, current.Velocity, alpha); interpolated.AngularVelocity = glm::mix(previous.AngularVelocity, current.AngularVelocity, alpha); } Finally here is how I retrieve the interpolated position (currently using only the position as a test phase) to feed it into the graphics module:
prop.Transform.setLocalPosition(prop.MoveableBody->GetInterpolatedPosition()); What could be wrong and the movement is shaky/jittery ? Let me know if you need to see more code.
