From 5e778431c3ff0bbbade5de7382699aa4377a455f Mon Sep 17 00:00:00 2001
From: "Stephen C. Wills" <staphen@gmail.com>
Date: Tue, 29 Aug 2023 07:46:49 -0400
Subject: [PATCH] Deterministic timer simulation for shrine messages in demo
 mode (#6516)

---
 Source/CMakeLists.txt      |  1 +
 Source/engine/demomode.cpp | 19 ++++++++++++++-----
 Source/engine/demomode.h   |  6 ++++++
 Source/error.cpp           |  5 +++--
 Source/minitext.cpp        |  5 +++--
 Source/utils/timer.cpp     | 10 ++++++++++
 Source/utils/timer.hpp     |  7 +++++++
 7 files changed, 44 insertions(+), 9 deletions(-)
 create mode 100644 Source/utils/timer.cpp
 create mode 100644 Source/utils/timer.hpp

diff --git a/Source/CMakeLists.txt b/Source/CMakeLists.txt
index 40e2e2396..112b45692 100644
--- a/Source/CMakeLists.txt
+++ b/Source/CMakeLists.txt
@@ -166,6 +166,7 @@ set(libdevilutionx_SRCS
   utils/str_cat.cpp
   utils/str_case.cpp
   utils/surface_to_clx.cpp
+  utils/timer.cpp
   utils/utf8.cpp)
 
 if(SUPPORTS_MPQ)
diff --git a/Source/engine/demomode.cpp b/Source/engine/demomode.cpp
index da025765a..02ad8182f 100644
--- a/Source/engine/demomode.cpp
+++ b/Source/engine/demomode.cpp
@@ -715,6 +715,9 @@ bool FetchMessage(SDL_Event *event, uint16_t *modState)
 void RecordGameLoopResult(bool runGameLoop)
 {
 	WriteDemoMsgHeader(runGameLoop ? DemoMsg::GameTick : DemoMsg::Rendering);
+
+	if (runGameLoop && !IsRunning())
+		LogicTick++;
 }
 
 void RecordMessage(const SDL_Event &event, uint16_t modState)
@@ -790,6 +793,12 @@ void RecordMessage(const SDL_Event &event, uint16_t modState)
 
 void NotifyGameLoopStart()
 {
+	LogicTick = 0;
+
+	if (IsRunning()) {
+		StartTime = SDL_GetTicks();
+	}
+
 	if (IsRecording()) {
 		const std::string path = StrCat(paths::PrefPath(), "demo_", RecordNumber, ".dmo");
 		DemoRecording = OpenFile(path.c_str(), "wb");
@@ -803,11 +812,6 @@ void NotifyGameLoopStart()
 		WriteLE32(DemoRecording, gSaveNumber);
 		WriteSettings(DemoRecording);
 	}
-
-	if (IsRunning()) {
-		StartTime = SDL_GetTicks();
-		LogicTick = 0;
-	}
 }
 
 void NotifyGameLoopEnd()
@@ -843,6 +847,11 @@ void NotifyGameLoopEnd()
 	}
 }
 
+uint32_t SimulateMillisecondsSinceStartup()
+{
+	return LogicTick * 50;
+}
+
 } // namespace demo
 
 } // namespace devilution
diff --git a/Source/engine/demomode.h b/Source/engine/demomode.h
index a18040635..59629c9d1 100644
--- a/Source/engine/demomode.h
+++ b/Source/engine/demomode.h
@@ -28,6 +28,8 @@ void RecordMessage(const SDL_Event &event, uint16_t modState);
 
 void NotifyGameLoopStart();
 void NotifyGameLoopEnd();
+
+uint32_t SimulateMillisecondsSinceStartup();
 #else
 inline void OverrideOptions()
 {
@@ -60,6 +62,10 @@ inline void NotifyGameLoopStart()
 inline void NotifyGameLoopEnd()
 {
 }
+inline uint32_t SimulateMillisecondsSinceStartup()
+{
+	return 0;
+}
 #endif
 
 } // namespace demo
diff --git a/Source/error.cpp b/Source/error.cpp
index c3ac72abc..5368d7adf 100644
--- a/Source/error.cpp
+++ b/Source/error.cpp
@@ -16,6 +16,7 @@
 #include "stores.h"
 #include "utils/algorithm/container.hpp"
 #include "utils/language.h"
+#include "utils/timer.hpp"
 
 namespace devilution {
 
@@ -30,7 +31,7 @@ const int LineWidth = 418;
 
 void InitNextLines()
 {
-	msgdelay = SDL_GetTicks();
+	msgdelay = GetMillisecondsSinceStartup();
 	TextLines.clear();
 
 	const std::string paragraphs = WordWrapString(DiabloMessages.front(), LineWidth, GameFont12, 1);
@@ -172,7 +173,7 @@ void DrawDiabloMsg(const Surface &out)
 		lineNumber += 1;
 	}
 
-	if (msgdelay > 0 && msgdelay <= SDL_GetTicks() - 3500) {
+	if (msgdelay > 0 && msgdelay <= GetMillisecondsSinceStartup() - 3500) {
 		msgdelay = 0;
 	}
 	if (msgdelay == 0) {
diff --git a/Source/minitext.cpp b/Source/minitext.cpp
index c67032e7e..46cfaba0f 100644
--- a/Source/minitext.cpp
+++ b/Source/minitext.cpp
@@ -20,6 +20,7 @@
 #include "playerdat.hpp"
 #include "textdat.h"
 #include "utils/language.h"
+#include "utils/timer.hpp"
 
 namespace devilution {
 
@@ -81,7 +82,7 @@ uint32_t CalculateTextSpeed(int nSFX)
 
 int CalculateTextPosition()
 {
-	uint32_t currTime = SDL_GetTicks();
+	uint32_t currTime = GetMillisecondsSinceStartup();
 
 	int y = (currTime - ScrollStart) / qtextSpd - 260;
 
@@ -165,7 +166,7 @@ void InitQTextMsg(_speech_id m)
 		LoadText(_(Speeches[m].txtstr));
 		qtextflag = true;
 		qtextSpd = CalculateTextSpeed(sfxnr);
-		ScrollStart = SDL_GetTicks();
+		ScrollStart = GetMillisecondsSinceStartup();
 	}
 	PlaySFX(sfxnr);
 }
diff --git a/Source/utils/timer.cpp b/Source/utils/timer.cpp
new file mode 100644
index 000000000..a9665d9ed
--- /dev/null
+++ b/Source/utils/timer.cpp
@@ -0,0 +1,10 @@
+#include "engine/demomode.h"
+
+namespace devilution {
+
+uint32_t GetMillisecondsSinceStartup()
+{
+	return (demo::IsRunning() || demo::IsRecording()) ? demo::SimulateMillisecondsSinceStartup() : SDL_GetTicks();
+}
+
+} // namespace devilution
diff --git a/Source/utils/timer.hpp b/Source/utils/timer.hpp
new file mode 100644
index 000000000..1bc7cde91
--- /dev/null
+++ b/Source/utils/timer.hpp
@@ -0,0 +1,7 @@
+#pragma once
+
+namespace devilution {
+
+uint32_t GetMillisecondsSinceStartup();
+
+}