Merge branch 'fix-inaccurate-fps-counter' into 'next'

Fix inaccuracies in FPS counter

Closes #1047

See merge request STJr/SRB2!2047

src/screen.c

@@ -478,11 +478,11 @@ double averageFPS = 0.0f;
 #define USE_FPS_SAMPLES
 
 #ifdef USE_FPS_SAMPLES
-#define FPS_SAMPLE_RATE (0.05) // How often to update FPS samples, in seconds
+#define MAX_FRAME_TIME 0.05
 #define NUM_FPS_SAMPLES (16) // Number of samples to store
 
-static double fps_samples[NUM_FPS_SAMPLES];
-static double updateElapsed = 0.0;
+static double total_frame_time = 0.0;
+static int frame_index;
 #endif
 
 static boolean fps_init = false;
@@ -505,34 +505,12 @@ void SCR_CalculateFPS(void)
 	fps_enter = fps_finish;
 
 #ifdef USE_FPS_SAMPLES
-	updateElapsed += frameElapsed;
-
-	if (updateElapsed >= FPS_SAMPLE_RATE)
-	{
-		static int sampleIndex = 0;
-		int i;
-
-		fps_samples[sampleIndex] = frameElapsed;
-
-		sampleIndex++;
-		if (sampleIndex >= NUM_FPS_SAMPLES)
-			sampleIndex = 0;
-
-		averageFPS = 0.0;
-		for (i = 0; i < NUM_FPS_SAMPLES; i++)
-		{
-			averageFPS += fps_samples[i];
-		}
-
-		if (averageFPS > 0.0)
-		{
-			averageFPS = 1.0 / (averageFPS / NUM_FPS_SAMPLES);
-		}
-	}
-
-	while (updateElapsed >= FPS_SAMPLE_RATE)
+	total_frame_time += frameElapsed;
+	if (frame_index++ >= NUM_FPS_SAMPLES || total_frame_time >= MAX_FRAME_TIME)
 	{
-		updateElapsed -= FPS_SAMPLE_RATE;
+		averageFPS = 1.0 / (total_frame_time / frame_index);
+		total_frame_time = 0.0;
+		frame_index = 0;
 	}
 #else
 	// Direct, unsampled counter.