Only call fmt::format_to when the FPS value updates

Don't even need to initialise the buffer since the last update time is set when DiabloInit is called, then as long as the loading screen takes more than a second the threshold gets hit to call format_to on the first frame of gameplay.

Source/engine/render/scrollrt.cpp

@@ -209,9 +209,7 @@ uint32_t sgdwCursHgtOld;
  */
 Bitset2d<MAXDUNX, MAXDUNY> dRendered;
 
-int frameend;
-int framerate;
-int framestart;
+int lastFpsUpdateInMs;
 
 const char *const PlayerModeNames[] = {
 	"standing",
@@ -1322,23 +1320,24 @@ void DrawView(const Surface &out, Point startPosition)
  */
 void DrawFPS(const Surface &out)
 {
-	char buf[12];
+	static int framesSinceLastUpdate = 0;
+	static fmt::memory_buffer buf {};
 
 	if (!frameflag || !gbActive) {
 		return;
 	}
 
-	frameend++;
-	uint32_t tc = SDL_GetTicks();
-	uint32_t frames = tc - framestart;
-	if (tc - framestart >= 1000) {
-		framestart = tc;
-		framerate = 1000 * frameend / frames;
-		frameend = 0;
-	}
-	const char *end = fmt::format_to_n(buf, sizeof(buf), FMT_COMPILE("{} FPS"), framerate).out;
-	string_view str { buf, static_cast<string_view::size_type>(end - buf) };
-	DrawString(out, str, Point { 8, 68 }, UiFlags::ColorRed);
+	framesSinceLastUpdate++;
+	uint32_t runtimeInMs = SDL_GetTicks();
+	uint32_t msSinceLastUpdate = runtimeInMs - lastFpsUpdateInMs;
+	if (msSinceLastUpdate >= 1000) {
+		lastFpsUpdateInMs = runtimeInMs;
+		int framerate = 1000 * framesSinceLastUpdate / msSinceLastUpdate;
+		framesSinceLastUpdate = 0;
+		buf.clear();
+		fmt::format_to(std::back_inserter(buf), FMT_COMPILE("{} FPS"), framerate);
+	};
+	DrawString(out, { buf.data(), buf.size() }, Point { 8, 68 }, UiFlags::ColorRed);
 }
 
 /**
@@ -1654,7 +1653,7 @@ void ScrollView()
 void EnableFrameCount()
 {
 	frameflag = true;
-	framestart = SDL_GetTicks();
+	lastFpsUpdateInMs = SDL_GetTicks();
 }
 
 void scrollrt_draw_game_screen()