From 69b8976c661a79007e29332a12f6afca95a02c5f Mon Sep 17 00:00:00 2001
From: Christoph Oelckers <coelckers@users.noreply.github.com>
Date: Sat, 11 Apr 2020 23:43:29 +0200
Subject: [PATCH] - GZDoom timer code added.

This may come in handy later.
---
 source/core/utility/i_time.cpp | 115 ++++++++++++++++++++++++++++++++-
 source/core/utility/i_time.h   |  23 +++++++
 2 files changed, 135 insertions(+), 3 deletions(-)

diff --git a/source/core/utility/i_time.cpp b/source/core/utility/i_time.cpp
index d43dc1b7a..a4177e191 100644
--- a/source/core/utility/i_time.cpp
+++ b/source/core/utility/i_time.cpp
@@ -36,8 +36,6 @@
 #include <chrono>
 #include <thread>
 #include "i_time.h"
-#include "c_cvars.h"
-#include "printf.h"
 
 //==========================================================================
 //
@@ -45,7 +43,12 @@
 //
 //==========================================================================
 
-static double TimeScale = 1.0;
+static uint64_t FirstFrameStartTime;
+static uint64_t CurrentFrameStartTime;
+static uint64_t FreezeTime;
+int GameTicRate;
+
+double TimeScale = 1.0;
 
 static uint64_t GetClockTimeNS()
 {
@@ -53,11 +56,82 @@ static uint64_t GetClockTimeNS()
 	return (uint64_t)((duration_cast<microseconds>(steady_clock::now().time_since_epoch()).count()) * (uint64_t)(TimeScale * 1000));
 }
 
+static uint64_t MSToNS(unsigned int ms)
+{
+	return static_cast<uint64_t>(ms) * 1'000'000;
+}
+
 static uint64_t NSToMS(uint64_t ns)
 {
 	return static_cast<uint64_t>(ns / 1'000'000);
 }
 
+static int NSToTic(uint64_t ns)
+{
+	return static_cast<int>(ns * GameTicRate / 1'000'000'000);
+}
+
+static uint64_t TicToNS(int tic)
+{
+	return static_cast<uint64_t>(tic) * 1'000'000'000 / GameTicRate;
+}
+
+void I_SetFrameTime()
+{
+	// Must only be called once per frame/swapbuffers.
+	//
+	// Caches all timing information for the current rendered frame so that any
+	// calls to I_GetTime or I_GetTimeFrac will return
+	// the same time.
+
+	if (FreezeTime == 0)
+	{
+		CurrentFrameStartTime = GetClockTimeNS();
+		if (FirstFrameStartTime == 0)
+			FirstFrameStartTime = CurrentFrameStartTime;
+	}
+}
+
+void I_WaitVBL(int count)
+{
+	// I_WaitVBL is never used to actually synchronize to the vertical blank.
+	// Instead, it's used for delay purposes. Doom used a 70 Hz display mode,
+	// so that's what we use to determine how long to wait for.
+
+	std::this_thread::sleep_for(std::chrono::milliseconds(1000 * count / 70));
+	I_SetFrameTime();
+}
+
+int I_WaitForTic(int prevtic)
+{
+	// Waits until the current tic is greater than prevtic. Time must not be frozen.
+
+	int time;
+	while ((time = I_GetTime()) <= prevtic)
+	{
+		// Windows-specific note:
+		// The minimum amount of time a thread can sleep is controlled by timeBeginPeriod.
+		// We set this to 1 ms in DoMain.
+
+		const uint64_t next = FirstFrameStartTime + TicToNS(prevtic + 1);
+		const uint64_t now = I_nsTime();
+
+		if (next > now)
+		{
+			const uint64_t sleepTime = NSToMS(next - now);
+
+			if (sleepTime > 2)
+			{
+				std::this_thread::sleep_for(std::chrono::milliseconds(sleepTime - 2));
+			}
+		}
+
+		I_SetFrameTime();
+	}
+
+	return time;
+}
+
 uint64_t I_nsTime()
 {
 	return GetClockTimeNS();
@@ -68,3 +142,38 @@ uint64_t I_msTime()
 	return NSToMS(I_nsTime());
 }
 
+uint64_t I_msTimeFS() // from "start"
+{
+	return (FirstFrameStartTime == 0) ? 0 : NSToMS(I_nsTime() - FirstFrameStartTime);
+}
+
+int I_GetTime()
+{
+	return NSToTic(CurrentFrameStartTime - FirstFrameStartTime);
+}
+
+double I_GetTimeFrac()
+{
+	int currentTic = NSToTic(CurrentFrameStartTime - FirstFrameStartTime);
+	uint64_t ticStartTime = FirstFrameStartTime + TicToNS(currentTic);
+	uint64_t ticNextTime = FirstFrameStartTime + TicToNS(currentTic + 1);
+
+	return (CurrentFrameStartTime - ticStartTime) / (double)(ticNextTime - ticStartTime);
+}
+
+void I_FreezeTime(bool frozen)
+{
+	if (frozen)
+	{
+		assert(FreezeTime == 0);
+		FreezeTime = GetClockTimeNS();
+	}
+	else
+	{
+		assert(FreezeTime != 0);
+		FirstFrameStartTime += GetClockTimeNS() - FreezeTime;
+		FreezeTime = 0;
+		I_SetFrameTime();
+	}
+}
+
diff --git a/source/core/utility/i_time.h b/source/core/utility/i_time.h
index 8c4274942..47d726de7 100644
--- a/source/core/utility/i_time.h
+++ b/source/core/utility/i_time.h
@@ -2,8 +2,31 @@
 
 #include <stdint.h>
 
+extern int GameTicRate;
+extern double TimeScale;
+
+// Called by D_DoomLoop, sets the time for the current frame
+void I_SetFrameTime();
+
+// Called by D_DoomLoop, returns current time in tics.
+int I_GetTime();
+
+double I_GetTimeFrac();
+
+// like I_GetTime, except it waits for a new tic before returning
+int I_WaitForTic(int);
+
+// Freezes tic counting temporarily. While frozen, calls to I_GetTime()
+// will always return the same value.
+// You must also not call I_WaitForTic() while freezing time, since the
+// tic will never arrive (unless it's the current one).
+void I_FreezeTime(bool frozen);
+
 // [RH] Returns millisecond-accurate time
 uint64_t I_msTime();
 
+// [SP] Returns millisecond-accurate time from start
+uint64_t I_msTimeFS();
+
 // Nanosecond-accurate time
 uint64_t I_nsTime();