Increase relative joystick movement based on input update time

For relative mouse movement in SDL, the `SDL_GetRelativeMouseState` function always returns distance that the mouse moved since the last call of this function.

For joysticks, we only have access to the current axis values and no accumulated values.
This made the relative joystick movement speed decrease a lot when the client's refresh rate is low.
This is now counteracted by measuring the average time between calls of `IInput::Update` and multiplying the joystick movement by this number.

Closes #6296.

src/engine/client/input.cpp

@@ -46,6 +46,9 @@ CInput::CInput()
 	mem_zero(m_aInputCount, sizeof(m_aInputCount));
 	mem_zero(m_aInputState, sizeof(m_aInputState));
 
+	m_LastUpdate = 0;
+	m_UpdateTime = 0.0f;
+
 	m_InputCounter = 1;
 	m_InputGrabbed = false;
 
@@ -220,7 +223,7 @@ bool CInput::CJoystick::Relative(float *pX, float *pY)
 	const float DeadZone = Input()->GetJoystickDeadzone();
 	if(Len > DeadZone)
 	{
-		const float Factor = 0.1f * maximum((Len - DeadZone) / (1 - DeadZone), 0.001f) / Len;
+		const float Factor = 2500.0f * Input()->GetUpdateTime() * maximum((Len - DeadZone) / (1.0f - DeadZone), 0.001f) / Len;
 		*pX = RawJoystickPos.x * Factor;
 		*pY = RawJoystickPos.y * Factor;
 		return true;
@@ -562,6 +565,14 @@ void CInput::SetEditingPosition(float X, float Y)
 
 int CInput::Update()
 {
+	const int64_t Now = time_get();
+	if(m_LastUpdate != 0)
+	{
+		const float Diff = (Now - m_LastUpdate) / (float)time_freq();
+		m_UpdateTime = m_UpdateTime == 0.0f ? Diff : (m_UpdateTime * 0.8f + Diff * 0.2f);
+	}
+	m_LastUpdate = Now;
+
 	// keep the counter between 1..0xFFFF, 0 means not pressed
 	m_InputCounter = (m_InputCounter % 0xFFFF) + 1;
 

src/engine/input.h

@@ -35,6 +35,8 @@ protected:
 	// quick access to events
 	int m_NumEvents;
 	IInput::CEvent m_aInputEvents[INPUT_BUFFER_SIZE];
+	int64_t m_LastUpdate;
+	float m_UpdateTime;
 
 public:
 	enum
@@ -66,6 +68,12 @@ public:
 	CEvent *GetEventsRaw() { return m_aInputEvents; }
 	int *GetEventCountRaw() { return &m_NumEvents; }
 
+	/**
+	 * @return Rolling average of the time in seconds between
+	 * calls of the Update function.
+	 */
+	float GetUpdateTime() const { return m_UpdateTime; }
+
 	// keys
 	virtual bool ModifierIsPressed() const = 0;
 	virtual bool ShiftIsPressed() const = 0;