From 58e447d8d01d5eb915ba58a8735e4dfffb942b77 Mon Sep 17 00:00:00 2001
From: RoosterDragon <RoosterDragon@outlook.com>
Date: Mon, 13 Nov 2023 18:12:05 +0000
Subject: [PATCH] Change FPS counter behaviour.

Calculate a rolling average of FPS over the last second. This allows the FPS counter to be updated every frame - and in particular means it can display a rough figure immediately rather than needing to wait one second to collect information at the start of a game.
---
 .../Widgets/Logic/PerfDebugLogic.cs           | 24 ++++++++++---------
 1 file changed, 13 insertions(+), 11 deletions(-)

diff --git a/OpenRA.Mods.Common/Widgets/Logic/PerfDebugLogic.cs b/OpenRA.Mods.Common/Widgets/Logic/PerfDebugLogic.cs
index ab6f44c012..f6e76719fb 100644
--- a/OpenRA.Mods.Common/Widgets/Logic/PerfDebugLogic.cs
+++ b/OpenRA.Mods.Common/Widgets/Logic/PerfDebugLogic.cs
@@ -9,6 +9,8 @@
  */
 #endregion
 
+using System;
+using System.Collections.Generic;
 using System.Diagnostics;
 using OpenRA.Graphics;
 using OpenRA.Support;
@@ -28,22 +30,22 @@ namespace OpenRA.Mods.Common.Widgets.Logic
 			perfText.IsVisible = () => Game.Settings.Debug.PerfText;
 
 			var fpsTimer = Stopwatch.StartNew();
-			var fpsReferenceFrame = Game.RenderFrame;
-			var fps = 0;
+			var frameTimings = new List<(int Frame, TimeSpan Time)>(32) { (Game.RenderFrame, TimeSpan.Zero) };
 			perfText.GetText = () =>
 			{
-				var elapsed = fpsTimer.ElapsedMilliseconds;
-				if (elapsed > 1000)
-				{
-					// Round to closest integer
-					fps = (int)(1000.0f * (Game.RenderFrame - fpsReferenceFrame) / fpsTimer.ElapsedMilliseconds + 0.5f);
-					fpsTimer.Restart();
-					fpsReferenceFrame = Game.RenderFrame;
-				}
+				// Calculate FPS as a rolling average over the last ~1 second of frames.
+				frameTimings.Add((Game.RenderFrame, fpsTimer.Elapsed));
+				var cutoffTime = frameTimings[^1].Time - TimeSpan.FromSeconds(1);
+				var firstIndexPastCutoff = frameTimings.FindIndex(ft => ft.Time >= cutoffTime);
+				if (frameTimings.Count - firstIndexPastCutoff >= 2) // Keep at least 2 items for comparing.
+					frameTimings.RemoveRange(0, firstIndexPastCutoff);
+				var (oldestFrame, oldestTime) = frameTimings[0];
+				var (newestFrame, newestTime) = frameTimings[^1];
+				var fps = (newestFrame - oldestFrame) / (newestTime - oldestTime).TotalSeconds;
 
 				var wfbSize = Game.Renderer.WorldFrameBufferSize;
 				var viewportSize = worldRenderer.Viewport.Rectangle.Size;
-				return $"FPS: {fps}\nTick {Game.LocalTick} @ {PerfHistory.Items["tick_time"].Average(Game.Settings.Debug.Samples):F1} ms\n" +
+				return $"FPS: {fps:0}\nTick {Game.LocalTick} @ {PerfHistory.Items["tick_time"].Average(Game.Settings.Debug.Samples):F1} ms\n" +
 					$"Render {Game.RenderFrame} @ {PerfHistory.Items["render"].Average(Game.Settings.Debug.Samples):F1} ms\n" +
 					$"Batches: {PerfHistory.Items["batches"].LastValue}\n" +
 					$"Viewport Size: {viewportSize.Width} x {viewportSize.Height} / {Game.Renderer.WorldDownscaleFactor}\n" +