Vsync makes character walk weirdly

[LHLaurini]

I've made a character controller from scratch. It's kinda simple, but works fine, except for when Vsync is on. I can't post the entire code because it would take about 200 lines, but it works like this:

• It is a normal btRigidBody, NOT kinematic.
• Gravity pulls it down like any btRigidBody
• Movement is made by btRigidBody::setLinearVelocity

This is the "core" function (it's not very organized, but does the trick):

Code: Select all

void ThirdPersonCharacter::ProcessInputInternal(XMFLOAT2& Move, XMFLOAT2& Look, bool Jump, bool Sprint)
{
	XMFLOAT3 Focus;
	XMStoreFloat3(&Focus, CharacterCamera.FocusPosition);
	CharacterCamera.SetCamera(Focus, CameraDistance, CharacterCamera.Rotation + XMFLOAT3(Look.y, Look.x, 0.0f));

	if (CharacterBody->getLinearVelocity().getY() <= 0)
	{
		CharacterState = OnGround ? Resting : Falling;
	}

	btScalar Friction(0), Damping(0);

	if (OnGround)
	{
		State LastCharacterState = CharacterState;
		btVector3 Velocity(0, 0, 0);

		Friction = 1000;
		Damping = LastCharacterState == Jumping ? 0 : 1;

		if (CharacterState != Jumping)
			CharacterState = Resting;

		if ((Move != XMFLOAT2(0, 0)) && (LastCharacterState != Jumping))
		{
			Friction = 1.0f;
			Damping = 0.0f;
			Velocity = btVector3(Move.x, 0, Move.y).rotate(btVector3(0, 1, 0), CharacterCamera.Rotation.y).normalize()
				* (Sprint ? 5 : 2.5);
			MeshRotation = CharacterCamera.Rotation.y;
			CharacterState = Walking;
		}

		if (Jump)
		{
			Friction = 1.0f;
			Damping = 0.0f;
			Velocity.setY(Velocity.getY() + 5);
			CharacterState = Jumping;
		}

		if (Velocity != btVector3(0, 0, 0))
			CharacterBody->setLinearVelocity(Velocity);
	}

	CharacterBody->setFriction(Friction);
	CharacterBody->setDamping(Damping, 0);
}

When Vsync is off everything seems to be fine. But when it's on, the problem varies (or doesn't happens) based on a single line of code. When...

• Code: Select all

  DynamicsWorld.stepSimulation(FrameTime, 10);

  Walking velocity is normal at the start, then it gets slower and slower until it stops and goes back to normal (and it goes on over again...)

• Code: Select all

  DynamicsWorld.stepSimulation(FrameTime, 0);

  Works perfectly fine, but I don't know if it's safe to do this. The docs say it disables the fixed timestep and uses the actual timestep, but I think that would be bad if the framerate drops (some objects could pass through others). Am I wrong?

• Code: Select all

  DynamicsWorld.stepSimulation(1.f / 60.f);

  This would not be a good thing, but I tried it only for testing purposes. It seems that whenever timeStep is equal to fixedTimeStep my character doesn't move at all (doesn't walk nor fall)

I'm very confused. These changes only seem to affect the character itself. Can someone help me? Please ask for more details if you need more.