Merge #5787

5787: Allow spectator mode to be changed while demo is paused r=def- a=Robyt3

By updating and rendering the current tick again when changing the spectator mode while the demo playback is paused. Closes #1843.

Refactoring: Extract `IDemoPlayer::ETickOffset`, `IDemoPlayer::SeekTick` and `CMenus::DemoSeekTick`.

## Checklist

- [X] Tested the change ingame
- [ ] Provided screenshots if it is a visual change
- [ ] Tested in combination with possibly related configuration options
- [ ] Written a unit test (especially base/) or added coverage to integration test
- [ ] Considered possible null pointers and out of bounds array indexing
- [ ] Changed no physics that affect existing maps
- [ ] Tested the change with [ASan+UBSan or valgrind's memcheck](https://github.com/ddnet/ddnet/#using-addresssanitizer--undefinedbehavioursanitizer-or-valgrinds-memcheck) (optional)


Co-authored-by: Robert Müller <robytemueller@gmail.com>

src/engine/demo.h

@@ -75,11 +75,19 @@ public:
 		DEMOTYPE_SERVER,
 	};
 
+	enum ETickOffset
+	{
+		TICK_CURRENT = 1, // update the current tick again
+		TICK_PREVIOUS = 0, // go to the previous tick
+		TICK_NEXT = 3, // go to the next tick
+	};
+
 	~IDemoPlayer() {}
 	virtual void SetSpeed(float Speed) = 0;
 	virtual void SetSpeedIndex(int Offset) = 0;
 	virtual int SeekPercent(float Percent) = 0;
 	virtual int SeekTime(float Seconds) = 0;
+	virtual int SeekTick(ETickOffset TickOffset) = 0;
 	virtual int SetPos(int WantedTick) = 0;
 	virtual void Pause() = 0;
 	virtual void Unpause() = 0;

src/engine/shared/demo.cpp

@@ -934,6 +934,11 @@ int CDemoPlayer::SeekTime(float Seconds)
 	return SetPos(WantedTick);
 }
 
+int CDemoPlayer::SeekTick(ETickOffset TickOffset)
+{
+	return SetPos(m_Info.m_Info.m_CurrentTick + (int)TickOffset);
+}
+
 int CDemoPlayer::SetPos(int WantedTick)
 {
 	if(!m_File)

src/engine/shared/demo.h

@@ -139,6 +139,7 @@ public:
 	void SetSpeedIndex(int Offset) override;
 	int SeekPercent(float Percent) override;
 	int SeekTime(float Seconds) override;
+	int SeekTick(ETickOffset TickOffset) override;
 	int SetPos(int WantedTick) override;
 	const CInfo *BaseInfo() const override { return &m_Info.m_Info; }
 	void GetDemoName(char *pBuffer, int BufferSize) const override;

src/game/client/components/menus.h

@@ -633,6 +633,7 @@ public:
 	int DoButton_CheckBox_Tristate(const void *pID, const char *pText, TRISTATE Checked, const CUIRect *pRect);
 	std::vector<CDemoItem> m_vDemos;
 	void DemolistPopulate();
+	void DemoSeekTick(IDemoPlayer::ETickOffset TickOffset);
 	bool m_Dummy;
 
 	const char *GetCurrentDemoFolder() const { return m_aCurrentDemoFolder; }

src/game/client/components/menus_demo.cpp

@@ -94,6 +94,16 @@ void CMenus::HandleDemoSeeking(float PositionToSeek, float TimeToSeek)
 	}
 }
 
+void CMenus::DemoSeekTick(IDemoPlayer::ETickOffset TickOffset)
+{
+	m_pClient->m_SuppressEvents = true;
+	DemoPlayer()->SeekTick(TickOffset);
+	m_pClient->m_SuppressEvents = false;
+	DemoPlayer()->Pause();
+	m_pClient->m_MapLayersBackGround.EnvelopeUpdate();
+	m_pClient->m_MapLayersForeGround.EnvelopeUpdate();
+}
+
 void CMenus::RenderDemoPlayer(CUIRect MainView)
 {
 	const IDemoPlayer::CInfo *pInfo = DemoPlayer()->BaseInfo();
@@ -270,12 +280,7 @@ void CMenus::RenderDemoPlayer(CUIRect MainView)
 		const bool TickBackwards = Input()->KeyPress(KEY_COMMA);
 		if(TickForwards || TickBackwards)
 		{
-			m_pClient->m_SuppressEvents = true;
-			DemoPlayer()->SetPos(pInfo->m_CurrentTick + (TickForwards ? 3 : 0));
-			m_pClient->m_SuppressEvents = false;
-			DemoPlayer()->Pause();
-			m_pClient->m_MapLayersBackGround.EnvelopeUpdate();
-			m_pClient->m_MapLayersForeGround.EnvelopeUpdate();
+			DemoSeekTick(TickForwards ? IDemoPlayer::TICK_NEXT : IDemoPlayer::TICK_PREVIOUS);
 		}
 	}
 

src/game/client/components/spectator.cpp

@@ -424,6 +424,9 @@ void CSpectator::Spectate(int SpectatorID)
 	if(Client()->State() == IClient::STATE_DEMOPLAYBACK)
 	{
 		m_pClient->m_DemoSpecID = clamp(SpectatorID, (int)SPEC_FOLLOW, MAX_CLIENTS - 1);
+		// The tick must be rendered for the spectator mode to be updated, so we do it manually when demo playback is paused
+		if(DemoPlayer()->BaseInfo()->m_Paused)
+			GameClient()->m_Menus.DemoSeekTick(IDemoPlayer::TICK_CURRENT);
 		return;
 	}