Add foreground FPS limit

config.h

@@ -18,5 +18,7 @@
 #define CFG_VID_DEFDISPLAY "-1"
 #define CFG_VID_DEFFULLSCREEN "0"
 #define CFG_VID_DEFRESIZABLE "0"
+#define CFG_VID_DEFFGFPS "30"
+#define CFG_VID_DEFBGFPS "5"
 #define CFG_VID_MINWIDTH 1080
 #define CFG_VID_MINHEIGHT 720

engine/core/core_video.cpp

@@ -48,6 +48,8 @@ class core_video_c: public core_IVideo, public conCmdHandler_c {
 	conVar_c* vid_fullscreen;
 	conVar_c* vid_resizable;
 	conVar_c* vid_last;
+	conVar_c* vid_fgfps;
+	conVar_c* vid_bgfps;
 
 	void	C_Vid_Apply(IConsole* conHnd, args_c &args);
 	void	C_Vid_ModeList(IConsole* conHnd, args_c &args);
@@ -71,6 +73,8 @@ core_video_c::core_video_c(sys_IMain* sysHnd)
 	vid_fullscreen	= sys->con->Cvar_Add("vid_fullscreen", CV_ARCHIVE, CFG_VID_DEFFULLSCREEN);
 	vid_resizable	= sys->con->Cvar_Add("vid_resizable", CV_ARCHIVE|CV_CLAMP, CFG_VID_DEFRESIZABLE, 0, 3);
 	vid_last		= sys->con->Cvar_Add("vid_last", CV_ARCHIVE, "");
+	vid_fgfps		= sys->con->Cvar_Add("vid_fgfps", CV_ARCHIVE|CV_CLAMP, CFG_VID_DEFFGFPS, 5, 120);
+	vid_bgfps		= sys->con->Cvar_Add("vid_bgfps", CV_ARCHIVE|CV_CLAMP, CFG_VID_DEFBGFPS, 5, 120);
 
 	Cmd_Add("vid_apply", 0, "", this, &core_video_c::C_Vid_Apply);
 	Cmd_Add("vid_modeList", 0, "", this, &core_video_c::C_Vid_ModeList);
@@ -111,6 +115,8 @@ void core_video_c::Apply(bool shown)
 	set.depth = 0;
 	set.minSize[0] = CFG_VID_MINWIDTH;
 	set.minSize[1] = CFG_VID_MINHEIGHT;
+	set.fgfps = vid_fgfps->intVal;
+	set.bgfps = vid_bgfps->intVal;
 	sys->video->Apply(&set);
 }
 

engine/system/sys_video.h

@@ -22,6 +22,8 @@ struct sys_vidSave_s {
 	int		size[2] = {};
 	int		pos[2] = {};
 	bool	maximised = false;
+	int		fgfps = 0;
+	int		bgfps = 0;
 };
 
 // Video settings structure
@@ -32,6 +34,8 @@ struct sys_vidSet_s {
 	int		mode[2] = {};	// Resolution or window size
 	int		depth = 0;		// Bit depth
 	int		minSize[2] = {};	// Minimum size for resizable windows
+	int		fgfps = 0;		// Foreground FPS limit
+	int		bgfps = 0;		// Background FPS limit
 	sys_vidSave_s save; // Saved state
 };
 

engine/system/win/sys_video.cpp

@@ -275,6 +275,9 @@ int sys_video_c::Apply(sys_vidSet_s* set)
 	vid.size[0] = wrec.right;
 	vid.size[1] = wrec.bottom;
 
+	vid.fgfps = cur.fgfps;
+	vid.bgfps = cur.bgfps;
+
 	// Process any messages generated during application
 	sys->RunMessages();
 

ui_main.cpp

@@ -6,6 +6,9 @@
 
 #include "ui_local.h"
 
+#include <chrono>
+#include <thread>
+
 // ======
 // Locals
 // ======
@@ -373,15 +376,16 @@ void ui_main_c::ScriptInit()
 
 void ui_main_c::Frame()
 {
+	const auto frameStart = std::chrono::high_resolution_clock::now();
+	auto fpsLimit = sys->video->vid.fgfps;
 	if (!sys->video->IsVisible() || sys->conWin->IsVisible() || restartFlag || didExit) {
 		framesSinceWindowHidden = 0;
 	}
 	else if (framesSinceWindowHidden <= 10) {
 		framesSinceWindowHidden++;
 	}
 	else if (!sys->video->IsActive() && !sys->video->IsCursorOverWindow()) {
-		sys->Sleep(100);
-		return;
+		fpsLimit = sys->video->vid.bgfps;
 	}	
 
 	if (renderer) {
@@ -425,8 +429,8 @@ void ui_main_c::Frame()
 	}
 
 	//sys->con->Printf("Finishing up...\n");
-	if ( !sys->video->IsActive() ) {
-		sys->Sleep(100);
+	if ( sys->video->IsActive() ) {
+		fpsLimit = sys->video->vid.fgfps;
 	}
 
 	while (restartFlag) {
@@ -436,6 +440,14 @@ void ui_main_c::Frame()
 		}
 		ScriptInit();
 	}
+
+	using FpMilliseconds = std::chrono::duration<float, std::chrono::milliseconds::period>;
+	const auto minimumFrameDuration = FpMilliseconds(1000.0f / fpsLimit);
+	const auto frameEnd = std::chrono::high_resolution_clock::now();
+	const auto frameDuration = std::chrono::duration_cast<FpMilliseconds>(frameEnd - frameStart);
+	if (frameDuration < minimumFrameDuration) {
+	  std::this_thread::sleep_for(minimumFrameDuration - frameDuration);
+	}
 }
 
 void ui_main_c::ScriptShutdown()