feat(file-loading): Improve FPS counter accuracy and video retention Enhance FPS counter stability by implementing a warmup period and explicit reset of appState.fps`, preventing erroneous spikes after new file loads.

Resolve infinite p5.js auto-draw loop during file processing by ensuring comprehensive UI cleanup and correct p5 instance lifecycle management (`redraw` instead of `lo`).

Introduce conditional video retention in `resetUIForNewLoad`, allowing the loaded video to persist when only new JSON data is supplied.

steps/src/dom.js

@@ -104,21 +104,36 @@ export const explorerBtn = document.getElementById("explorer-btn");
 
 //----------------------Reset UI for New file Load----------------------//
 // Resets the UI to make sure everything is clean before new files load.
-export function resetUIForNewLoad() {
-    console.log("Resetting UI for new file load.");
+// @param {boolean} isNewVideo - If true, the video player will be reset. If false, existing video is preserved.
+export function resetUIForNewLoad(isNewVideo = true) {
+    console.log(`Resetting UI for new file load. New Video: ${isNewVideo}`);
 
     // Hide feature toggles
     featureToggles.classList.add("hidden");
 
-    // Show placeholders
+    // Reset the FPS counter state to prevent incorrect calculations on reload
+    appState.fps = 0;
+
+    // --- Conditional Video Reset ---
+    if (isNewVideo || !videoPlayer.src) {
+        // Reset video UI: Show placeholder, hide player, clear source
+        videoPlaceholder.classList.remove('hidden');
+        videoPlayer.classList.add('hidden');
+        videoPlayer.src = ''; // Clear the video source
+        videoInfoOverlay.classList.add('hidden');
+    } else {
+        // Preserve video UI: Ensure player is visible, placeholder hidden
+        videoPlaceholder.classList.add('hidden');
+        videoPlayer.classList.remove('hidden');
+        // Do NOT clear videoPlayer.src
+        videoInfoOverlay.classList.remove('hidden');
+    }
+
+    // Show canvas placeholder (will be hidden later if data loads)
     canvasPlaceholder.style.display = 'flex';
-    videoPlaceholder.classList.remove('hidden');
     
-    // Hide video player and overlays
-    videoPlayer.classList.add('hidden');
-    videoPlayer.src = ''; // Clear the video source
+    // Always hide radar overlay initially
     radarInfoOverlay.classList.add('hidden');
-    videoInfoOverlay.classList.add('hidden');
     
     // Remove the p5 sketches completely
     if (appState.p5_instance) {

steps/src/fileLoader.js

@@ -30,6 +30,7 @@ import {
   speedSlider,
   updatePersistentOverlays,
   updateDebugOverlay,
+  resetUIForNewLoad,
 } from "./dom.js";
 
 /**
@@ -58,6 +59,11 @@ export function handleFiles(files, fromCache = false) {
 }
 
 async function processFilePipeline(jsonFile, videoFile, fromCache) {
+  // 0. Reset the UI to a clean state before processing anything.
+  // Pass 'true' if a new video is present, 'false' if we should try to keep the old one.
+  const isNewVideo = !!videoFile;
+  resetUIForNewLoad(isNewVideo);
+
   // 1. Show the unified loading modal.
   showLoadingModal("Processing files...");
 
@@ -298,8 +304,9 @@ function finalizeSetup() {
   if (!appState.p5_instance) {
     appState.p5_instance = new p5(radarSketch);
   } else {
-    // If it existed, ensure it's looping/active
-     appState.p5_instance.loop();
+    // If it existed, ensure it's up to date. 
+    // CRITICAL: Do NOT call .loop(). The app uses a custom animationLoop in sync.js.
+    appState.p5_instance.redraw();
   }
 
   if (!appState.zoomSketchInstance) {

steps/src/p5/radarSketch.js

@@ -48,6 +48,7 @@ export const radarSketch = function (p) {
 
   // --- START: FPS Calculation Variables ---
   let lastFrameTime = 0;
+  let framesDrawn = 0;
   // --- END: FPS Calculation Variables ---
 
   // Helper function to allow other sketches to access the static background
@@ -126,6 +127,10 @@ export const radarSketch = function (p) {
     p.drawTrackLegendToBuffer(); // Call the new function to draw the legend
 
     drawStaticRegionsToBuffer(p, staticBackgroundBuffer, plotScales);
+    
+    // Reset FPS state to prevent stale values from previous sessions
+    appState.fps = 0; 
+    
     p.noLoop();
     // Disable continuous looping, redraw will be called manually
   };
@@ -136,18 +141,28 @@ export const radarSketch = function (p) {
     }
 
     // --- START: FPS Calculation & Display ---
+    framesDrawn++;
     const currentTime = p.millis();
-    if (lastFrameTime > 0) {
+    
+    // Skip FPS calculation during the first few frames to avoid initialization spikes.
+    // This prevents the "300+ FPS" bug caused by the race between auto-draw and first redraw.
+    if (framesDrawn < 10) {
+      lastFrameTime = currentTime;
+    } else {
       const delta = currentTime - lastFrameTime;
       if (delta > 0) {
         const currentFps = 1000 / delta;
-        // Use exponential moving average for smoothing
-        const smoothingFactor = 0.95;
-        appState.fps =
-          appState.fps * smoothingFactor + currentFps * (1 - smoothingFactor);
+        // On the first valid calculation, snap to the current FPS to avoid slow ramp-up.
+        // Otherwise, use exponential moving average for smoothing.
+        if (framesDrawn === 10 || appState.fps === 0) {
+          appState.fps = currentFps;
+        } else {
+          const smoothingFactor = 0.95;
+          appState.fps = appState.fps * smoothingFactor + currentFps * (1 - smoothingFactor);
+        }
       }
+      lastFrameTime = currentTime;
     }
-    lastFrameTime = currentTime;
     // --- END: FPS Calculation & Display ---
 
     // Set background color based on current theme (dark/light)