qcommon: never sleep with common.framerate.max -2

src/engine/qcommon/common.cpp

@@ -883,6 +883,8 @@ void Com_Frame()
 		Sys::Error( "Shutting down to prevent time overflow" );
 	}
 
+	bool sleep = true;
+
 	// we may want to spin here if things are going too fast
 	if ( !cvar_demo_timedemo.Get() )
 	{
@@ -907,11 +909,10 @@ void Com_Frame()
 				max = maxfps.Get();
 			}
 
-			// A positive maxfps caps the fps to the given number, with an implicit
-			// cap at 333fps to avoid bugs. Above 333fps minMsec is less than 3.
-			// At 1 or 2 minMsec, the game still runs but exhibits various issues
-			// such as first-person weapon model flickering, or client having
-			// connection issues with server.
+			/* A positive maxfps caps the fps to the given number, with an implicit
+			cap at 333fps to avoid bugs. Above 333fps minMsec is less than 3 and with
+			minMsec being 2 or less some variables may become zero and some code may
+			experience division by zero. */
 			if ( max > 0 )
 			{
 				minMsec = std::max( 1000 / max, 3 );
@@ -921,11 +922,18 @@ void Com_Frame()
 			{
 				minMsec = 3;
 			}
-			// A negative maxfps really unlocks fps (and bugs).
-			else
+			/* A negative maxfps unlocks fps more (and unfortunate bugs) but cap
+			it to 1000 (because of a remaining sleep it's a bit less than that). */
+			else if ( max == -1 )
 			{
 				minMsec = 1;
 			}
+			// A maxfps smaller than -1 unlocks all remaining fps (and expected bugs). 
+			else
+			{
+				minMsec = 0;
+				sleep = false;
+			}
 		}
 	}
 	else
@@ -949,15 +957,18 @@ void Com_Frame()
 
 	IN_Frame(); // must be called at least once
 
-	while ( msec < minMsec )
+	if ( sleep )
 	{
-		//give cycles back to the OS
-		Sys::SleepFor(std::chrono::milliseconds(std::min(minMsec - msec, 50)));
-		IN_Frame();
+		while ( msec < minMsec )
+		{
+			//give cycles back to the OS
+			Sys::SleepFor(std::chrono::milliseconds(std::min(minMsec - msec, 50)));
+			IN_Frame();
 
-		Com_EventLoop();
-		com_frameTime = Sys::Milliseconds();
-		msec = com_frameTime - lastTime;
+			Com_EventLoop();
+			com_frameTime = Sys::Milliseconds();
+			msec = com_frameTime - lastTime;
+		}
 	}
 
 	IN_FrameEnd();