Handle the sleep at the end of D_SRB2Loop instead of the start

Simplifies logic in the other parts of the loop, and fixes problems with it frequently waiting too long.

src/d_main.c

@@ -687,29 +687,6 @@ static void D_Display(void)
 	}
 }
 
-static boolean D_CheckFrameCap(void)
-{
-	static boolean init = false;
-	static precise_t startCap = 0;
-	precise_t endCap = 0;
-
-	endCap = I_GetPreciseTime();
-
-	if (init == false)
-	{
-		startCap = endCap;
-		init = true;
-	}
-	else if (I_CheckFrameCap(startCap, endCap))
-	{
-		// Framerate should be capped.
-		return true;
-	}
-
-	startCap = endCap;
-	return false;
-}
-
 // =========================================================================
 // D_SRB2Loop
 // =========================================================================
@@ -720,10 +697,13 @@ void D_SRB2Loop(void)
 {
 	tic_t oldentertics = 0, entertic = 0, realtics = 0, rendertimeout = INFTICS;
 	static lumpnum_t gstartuplumpnum;
-	boolean ticked;
-	boolean interp;
+
+	boolean ticked = false;
+	boolean interp = false;
 	boolean doDisplay = false;
-	boolean frameCap = false;
+
+	precise_t frameTime = 0;
+	int frameElapsed = 0;
 
 	if (dedicated)
 		server = true;
@@ -775,6 +755,9 @@ void D_SRB2Loop(void)
 
 	for (;;)
 	{
+		frameTime = I_GetPreciseTime();
+		frameElapsed = 0;
+
 		if (lastwipetic)
 		{
 			oldentertics = lastwipetic;
@@ -804,19 +787,6 @@ void D_SRB2Loop(void)
 		doDisplay = false;
 		ticked = false;
 
-		frameCap = D_CheckFrameCap();
-
-		// Moved to here from I_FinishUpdate.
-		// It doesn't track fades properly anymore by being here (might be easy fix),
-		// but it's a little more accurate for actual rendering when its here.
-		SCR_CalculateFPS();
-
-		if (!realtics && !singletics)
-		{
-			if (frameCap)
-				continue;
-		}
-
 #ifdef HW3SOUND
 		HW3S_BeginFrameUpdate();
 #endif
@@ -872,15 +842,6 @@ void D_SRB2Loop(void)
 				tictime = entertime;
 			}
 
-			// Handle interp sleep / framerate cap here.
-			// TryRunTics needs ran if possible to prevent lagged map changes,
-			// (and if that runs, the code above needs to also run)
-			// so this is done here after TryRunTics.
-			if (frameCap)
-			{
-				continue;
-			}
-
 			if (!(paused || P_AutoPause()))
 			{
 #if 0
@@ -912,11 +873,6 @@ void D_SRB2Loop(void)
 		}
 		else
 		{
-			if (frameCap)
-			{
-				continue;
-			}
-
 			renderdeltatics = realtics * FRACUNIT;
 			rendertimefrac = FRACUNIT;
 		}
@@ -940,6 +896,19 @@ void D_SRB2Loop(void)
 #endif
 
 		LUA_Step();
+
+		// Moved to here from I_FinishUpdate.
+		// It doesn't track fades properly anymore by being here (might be easy fix),
+		// but it's a little more accurate for actual rendering when its here.
+		SCR_CalculateFPS();
+
+		// Fully completed frame made, handle frame cap delay.
+		frameElapsed = I_PreciseToMicros(I_GetPreciseTime() - frameTime);
+
+		if (!singletics)
+		{
+			I_FrameCapSleep(frameElapsed);
+		}
 	}
 }
 

src/i_system.h

@@ -58,13 +58,17 @@ precise_t I_GetPreciseTime(void);
   */
 int I_PreciseToMicros(precise_t d);
 
-/**	\brief	The I_Sleep function
+/**	\brief	Sleeps by the value of cv_sleep
 
 	\return	void
 */
 void I_Sleep(void);
 
-boolean I_CheckFrameCap(precise_t start, precise_t end);
+/**	\brief	Sleeps for a variable amount of time, depending on how much time the last frame took.
+
+	\return	void
+*/
+boolean I_FrameCapSleep(const int elapsed);
 
 /**	\brief Get events
 

src/screen.c

@@ -509,7 +509,7 @@ void SCR_DisplayTicRate(void)
 	INT32 ticcntcolor = 0;
 	const INT32 h = vid.height-(8*vid.dupy);
 	UINT32 cap = R_GetFramerateCap();
-	double fps = ceil(averageFPS);
+	double fps = round(averageFPS);
 
 	if (gamestate == GS_NULL)
 		return;
@@ -525,10 +525,11 @@ void SCR_DisplayTicRate(void)
 		ticcntcolor = V_GREENMAP;
 	}
 
-
 	if (cv_ticrate.value == 2) // compact counter
-		V_DrawString(vid.width-(32*vid.dupx), h,
-			ticcntcolor|V_NOSCALESTART|V_USERHUDTRANS, va("%04.0f", fps));
+	{
+		V_DrawRightAlignedString(vid.width, h,
+			ticcntcolor|V_NOSCALESTART|V_USERHUDTRANS, va("%04.2f", averageFPS)); // use averageFPS directly
+	}
 	else if (cv_ticrate.value == 1) // full counter
 	{
 		if (cap > 0)

src/sdl/i_system.c

@@ -2167,6 +2167,10 @@ float I_GetTimeFrac(void)
 	return elapsed_tics;
 }
 
+//
+// I_GetPreciseTime
+// returns time in precise_t
+//
 precise_t I_GetPreciseTime(void)
 {
 	return SDL_GetPerformanceCounter();
@@ -2184,7 +2188,7 @@ int I_PreciseToMicros(precise_t d)
 }
 
 //
-//I_StartupTimer
+// I_StartupTimer
 //
 void I_StartupTimer(void)
 {
@@ -2195,71 +2199,82 @@ void I_StartupTimer(void)
 	elapsed_tics    = 0.0;
 }
 
+//
+// I_Sleep
+// Sleeps by the value of cv_sleep
+//
 void I_Sleep(void)
 {
 	if (cv_sleep.value != -1)
 		SDL_Delay(cv_sleep.value);
 }
 
-boolean I_CheckFrameCap(precise_t start, precise_t end)
+//
+// I_FrameCapSleep
+// Sleeps for a variable amount of time, depending on how much time the last frame took.
+//
+boolean I_FrameCapSleep(const int elapsed)
 {
+	const INT64 delayGranularity = 2000;
+	// I picked 2ms as it's what GZDoom uses before it stops trying to sleep,
+	// but maybe other values might work better.
+
 	const UINT32 capFrames = R_GetFramerateCap();
 	int capMicros = 0;
 
-	int elapsed;
-
 	if (capFrames == 0)
 	{
 		// We don't want to cap.
 		return false;
 	}
 
-	elapsed = I_PreciseToMicros(end - start);
 	capMicros = 1000000 / capFrames;
 
 	if (elapsed < capMicros)
 	{
-		// Experimental variable delay code.
-		if (cv_sleep.value > 0)
+		const INT64 error = capMicros / 40;
+		// 2.5% ... How much we might expect the framerate to flucuate.
+		// No exact logic behind this number, simply tried stuff until the framerate
+		// reached the cap 300 more often and only overshot it occasionally.
+
+		INT64 wait = (capMicros - elapsed) - error;
+
+		while (wait > 0)
 		{
-			const INT64 delayGranularity = 2000; // 2ms, I picked this as it's what GZDoom uses before it stops trying to sleep.
-			INT64 wait = (capMicros - elapsed);
+			precise_t sleepStart = I_GetPreciseTime();
+			precise_t sleepEnd = sleepStart;
+			int sleepElasped = 0;
 
-			while (wait > 0)
+			if (wait > delayGranularity && cv_sleep.value != -1)
 			{
-				precise_t sleepStart = I_GetPreciseTime();
-				precise_t sleepEnd = sleepStart;
-				int sleepElasped = 0;
+				// Wait 1ms at a time (on default settings)
+				// until we're close enough.
+				SDL_Delay(cv_sleep.value);
 
-				if (wait > delayGranularity)
+				sleepEnd = I_GetPreciseTime();
+				sleepElasped = I_PreciseToMicros(sleepEnd - sleepStart);
+			}
+			else
+			{
+				// When we have an extremely fine wait,
+				// we do this to spin-lock the remaining time.
+				while (sleepElasped < wait)
 				{
-					// Wait 1ms at a time (on default settings)
-					// until we're close enough.
-					SDL_Delay(cv_sleep.value);
-
 					sleepEnd = I_GetPreciseTime();
 					sleepElasped = I_PreciseToMicros(sleepEnd - sleepStart);
 				}
-				else
-				{
-					// When we have an extremely fine wait,
-					// we do this to spin-lock the remaining time.
 
-					while (sleepElasped < wait)
-					{
-						sleepEnd = I_GetPreciseTime();
-						sleepElasped = I_PreciseToMicros(sleepEnd - sleepStart);
-					}
-				}
-
-				wait -= sleepElasped;
+				break;
 			}
+
+			wait -= sleepElasped;
 		}
 
+		// We took our nap.
 		return true;
 	}
 
-	// Waited enough to draw again.
+	// We're lagging behind.
 	return false;
 }