Updated Fps counter

source/funkin/backend/system/framerate/FramerateCounter.hx

@@ -1,17 +1,26 @@
 package funkin.backend.system.framerate;
 
+import haxe.ds.Vector;
 import openfl.display.Sprite;
 import openfl.text.TextField;
 import openfl.text.TextFormat;
 
+inline final FRAME_TIME_HISTORY = 20;
+
 class FramerateCounter extends Sprite {
 	public var fpsNum:TextField;
 	public var fpsLabel:TextField;
-	public var lastFPS:Float = 0;
+
+	public var fpsHistoryIndex:Int = 0;
+	public var fpsHistory:Vector<Float>;
 
 	public function new() {
 		super();
 
+		fpsHistory = new Vector(FRAME_TIME_HISTORY);
+		// Initialize to 60 FPS, so that the initial estimation until we get enough data is always reasonable.
+		fpsHistory.fill(1000.0 / 60.0);
+
 		fpsNum = new TextField();
 		fpsLabel = new TextField();
 
@@ -30,8 +39,20 @@ class FramerateCounter extends Sprite {
 		if (alpha <= 0.05) return;
 		super.__enterFrame(t);
 
-		lastFPS = CoolUtil.fpsLerp(lastFPS, FlxG.elapsed == 0 ? 0 : (1 / FlxG.elapsed), 0.25);
-		fpsNum.text = Std.string(Math.floor(lastFPS));
+		// todo use gpu time
+		fpsHistory[fpsHistoryIndex] = FlxG.elapsed * 1000;
+		fpsHistoryIndex = (fpsHistoryIndex + 1) % FRAME_TIME_HISTORY;
+
+		// Calculate average CPU time.
+		// Code based on Godot's FPS counter.
+		var cpuTime = 0.0;
+		for(i in 0...FRAME_TIME_HISTORY) {
+			cpuTime += fpsHistory[i];
+		}
+		cpuTime /= FRAME_TIME_HISTORY;
+		cpuTime = Math.max(0.01, cpuTime); // Prevent unrealistically low values.
+
+		fpsNum.text = Std.string(Math.floor(1000.0 / cpuTime));
 		fpsLabel.x = fpsNum.x + fpsNum.width;
 		fpsLabel.y = (fpsNum.y + fpsNum.height) - fpsLabel.height;
 	}