From 8d2745fc33352c84ad32664567c922a627040994 Mon Sep 17 00:00:00 2001
From: Muzychenko Andrey <33288308+k4zmu2a@users.noreply.github.com>
Date: Sun, 3 Oct 2021 18:06:19 +0300
Subject: [PATCH] Added support for sub-millisecond frame times.

---
 SpaceCadetPinball/pb.cpp      | 23 ++++++++++++++---------
 SpaceCadetPinball/pb.h        |  4 ++--
 SpaceCadetPinball/winmain.cpp | 15 +++++++--------
 3 files changed, 23 insertions(+), 19 deletions(-)

diff --git a/SpaceCadetPinball/pb.cpp b/SpaceCadetPinball/pb.cpp
index b484115..d27b35f 100644
--- a/SpaceCadetPinball/pb.cpp
+++ b/SpaceCadetPinball/pb.cpp
@@ -30,7 +30,7 @@
 TPinballTable* pb::MainTable = nullptr;
 DatFile* pb::record_table = nullptr;
 int pb::time_ticks = 0, pb::demo_mode = 0, pb::cheat_mode = 0, pb::game_mode = 2, pb::mode_countdown_;
-float pb::time_now, pb::time_next, pb::ball_speed_limit;
+float pb::time_now = 0, pb::time_next = 0, pb::ball_speed_limit, pb::time_ticks_remainder = 0;
 high_score_struct pb::highscore_table[5];
 bool pb::FullTiltMode = false;
 
@@ -209,26 +209,31 @@ void pb::ballset(int x, int y)
 	ball->Speed = maths::normalize_2d(&ball->Acceleration);
 }
 
-void pb::frame(int dtMilliSec)
+void pb::frame(float dtMilliSec)
 {
 	if (dtMilliSec > 100)
 		dtMilliSec = 100;
-	if (dtMilliSec <= 0)
+	if (dtMilliSec < 0)
 		return;
-	float dtMicroSec = dtMilliSec * 0.001f;
+	float dtSec = dtMilliSec * 0.001f;
 	if (!mode_countdown(dtMilliSec))
 	{
-		time_next = time_now + dtMicroSec;
-		timed_frame(time_now, dtMicroSec, true);
+		time_next = time_now + dtSec;
+		timed_frame(time_now, dtSec, true);
 		time_now = time_next;
-		time_ticks += dtMilliSec;
+
+		dtMilliSec += time_ticks_remainder;
+		auto dtWhole = static_cast<int>(dtMilliSec);
+		time_ticks_remainder = dtMilliSec - static_cast<float>(dtWhole);
+		time_ticks += dtWhole;
+
 		if (nudge::nudged_left || nudge::nudged_right || nudge::nudged_up)
 		{
-			nudge::nudge_count = dtMicroSec * 4.0f + nudge::nudge_count;
+			nudge::nudge_count = dtSec * 4.0f + nudge::nudge_count;
 		}
 		else
 		{
-			auto nudgeDec = nudge::nudge_count - dtMicroSec;
+			auto nudgeDec = nudge::nudge_count - dtSec;
 			if (nudgeDec <= 0.0f)
 				nudgeDec = 0.0;
 			nudge::nudge_count = nudgeDec;
diff --git a/SpaceCadetPinball/pb.h b/SpaceCadetPinball/pb.h
index 17bd97e..155deb7 100644
--- a/SpaceCadetPinball/pb.h
+++ b/SpaceCadetPinball/pb.h
@@ -33,7 +33,7 @@ class pb
 {
 public:
 	static int time_ticks;
-	static float ball_speed_limit, time_now, time_next;
+	static float ball_speed_limit, time_now, time_next, time_ticks_remainder;
 	static int cheat_mode, game_mode;
 	static DatFile* record_table;
 	static TPinballTable* MainTable;
@@ -48,7 +48,7 @@ public:
 	static void toggle_demo();
 	static void replay_level(int demoMode);
 	static void ballset(int x, int y);
-	static void frame(int dtMilliSec);
+	static void frame(float dtMilliSec);
 	static void timed_frame(float timeNow, float timeDelta, bool drawBalls);
 	static void window_size(int* width, int* height);
 	static void pause_continue();
diff --git a/SpaceCadetPinball/winmain.cpp b/SpaceCadetPinball/winmain.cpp
index 16ac96a..87a8d1d 100644
--- a/SpaceCadetPinball/winmain.cpp
+++ b/SpaceCadetPinball/winmain.cpp
@@ -154,8 +154,8 @@ int winmain::WinMain(LPCSTR lpCmdLine)
 	DWORD dtHistoryCounter = 300u, updateCounter = 0, frameCounter = 0;
 
 	auto frameStart = Clock::now();
-	double frameDuration = TargetFrameTime.count(), UpdateToFrameCounter = 0;
-	DurationMs sleepRemainder(0);
+	double UpdateToFrameCounter = 0;
+	DurationMs sleepRemainder(0), frameDuration(TargetFrameTime);
 	auto prevTime = frameStart;
 	while (true)
 	{
@@ -219,12 +219,12 @@ int winmain::WinMain(LPCSTR lpCmdLine)
 			}
 			if (!single_step)
 			{
-				auto deltaT = static_cast<int>(frameDuration);
-				frameDuration -= deltaT;
-				pb::frame(deltaT);
+				auto dt = static_cast<float>(frameDuration.count());
+				auto dtWhole = static_cast<int>(std::round(dt));
+				pb::frame(dt);
 				if (gfr_display)
 				{
-					auto deltaTPal = deltaT + 10;
+					auto deltaTPal = dtWhole + 10;
 					auto fillChar = static_cast<uint8_t>(deltaTPal);
 					if (deltaTPal > 236)
 					{
@@ -277,8 +277,7 @@ int winmain::WinMain(LPCSTR lpCmdLine)
 			}
 
 			// Limit duration to 2 * target time
-			frameDuration = std::min(frameDuration + DurationMs(frameEnd - frameStart).count(),
-			                         2 * TargetFrameTime.count());
+			frameDuration = std::min<DurationMs>(DurationMs(frameEnd - frameStart), 2 * TargetFrameTime);
 			frameStart = frameEnd;
 			UpdateToFrameCounter++;
 		}