fix: two-pass start, depth cap, cssText restore on stop

lib/gravity-engine.ts

@@ -15,7 +15,7 @@ interface PhysicsBody {
 
 export class GravityEngine {
   private bodies: PhysicsBody[] = [];
-  private dirtyElements: HTMLElement[] = [];
+  private dirtyElements: Array<{ el: HTMLElement; originalCssText: string }> = [];
   private animationFrameId: number | null = null;
   private isRunning = false;
 
@@ -26,51 +26,65 @@ export class GravityEngine {
     this.isRunning = true;
     this.dirtyElements = [];
 
+    const MAX_DEPTH = 3;
     const containers = document.querySelectorAll(".gravity-body");
     const leafElements: HTMLElement[] = [];
+    const intermediates: { el: HTMLElement; w: number; h: number }[] = [];
+
+    // READ-ONLY traversal: classify all elements and snapshot sizes.
+    // No DOM writes here — one layout flush for the entire traversal.
+    const collectElements = (el: HTMLElement, depth: number) => {
+      // Skip purely decorative elements (e.g. background images).
+      if (el.classList.contains("pointer-events-none")) return;
 
-    // Phase 1 — Size-lock: freeze intermediate container dimensions
-    // so they don't collapse when children become position:fixed.
-    const extractLeaves = (el: HTMLElement) => {
       const isSolid = ["SVG", "IMG", "BUTTON", "IFRAME", "A"].includes(
         el.tagName.toUpperCase(),
       );
 
-      if (isSolid || el.children.length === 0) {
+      // Treat as a leaf if solid, childless, or at the depth cap.
+      if (isSolid || el.children.length === 0 || depth >= MAX_DEPTH) {
         if (el.offsetWidth > 0 && el.offsetHeight > 0) {
           leafElements.push(el);
         }
         return;
       }
 
-      el.style.width = `${el.offsetWidth}px`;
-      el.style.height = `${el.offsetHeight}px`;
-      this.dirtyElements.push(el);
-
+      intermediates.push({ el, w: el.offsetWidth, h: el.offsetHeight });
       Array.from(el.children).forEach((child) =>
-        extractLeaves(child as HTMLElement),
+        collectElements(child as HTMLElement, depth + 1),
       );
     };
 
+    const rootSizes: { el: HTMLElement; w: number; h: number }[] = [];
     containers.forEach((container) => {
       const htmlContainer = container as HTMLElement;
-      htmlContainer.style.width = `${htmlContainer.offsetWidth}px`;
-      htmlContainer.style.height = `${htmlContainer.offsetHeight}px`;
-      this.dirtyElements.push(htmlContainer);
-
+      rootSizes.push({
+        el: htmlContainer,
+        w: htmlContainer.offsetWidth,
+        h: htmlContainer.offsetHeight,
+      });
       Array.from(htmlContainer.children).forEach((child) =>
-        extractLeaves(child as HTMLElement),
+        collectElements(child as HTMLElement, 0),
       );
     });
 
-    // Phase 2 — Read: batch all getBoundingClientRect() before any writes.
+    // WRITE PASS 1: size-lock roots and intermediates so they don't collapse
+    // when their children become position:fixed.
+    [...rootSizes, ...intermediates].forEach(({ el, w, h }) => {
+      this.dirtyElements.push({ el, originalCssText: el.style.cssText });
+      el.style.width = `${w}px`;
+      el.style.height = `${h}px`;
+    });
+
+    // READ PASS 2: batch all getBoundingClientRect calls before any leaf writes.
     const snapshots = leafElements.map((el) => ({
       el,
       rect: el.getBoundingClientRect(),
     }));
 
-    // Phase 3 — Write: apply fixed positioning using snapshotted rects.
+    // WRITE PASS 2: apply fixed positioning to leaves using snapshotted rects.
     this.bodies = snapshots.map(({ el, rect }) => {
+      this.dirtyElements.push({ el, originalCssText: el.style.cssText });
       el.style.width = `${rect.width}px`;
       el.style.height = `${rect.height}px`;
       el.style.margin = "0px";
@@ -78,7 +92,6 @@ export class GravityEngine {
       el.style.left = "0px";
       el.style.top = "0px";
       el.style.transform = `translate(${rect.left}px, ${rect.top}px)`;
-      this.dirtyElements.push(el);
 
       const body: PhysicsBody = {
         el,
@@ -117,22 +130,16 @@ export class GravityEngine {
       body.el.style.transform = `translate(${body.originX}px, ${body.originY}px)`;
     });
 
-    // After the transition completes, clear all inline styles from every
-    // element we touched so the document flow is fully restored.
+    // After the transition completes, restore every element's original inline
+    // styles so document flow is fully recovered — including elements that had
+    // pre-existing inline styles we must not erase (e.g. Next.js fill images).
     const elementsToClear = [...this.dirtyElements];
     this.bodies = [];
     this.dirtyElements = [];
 
     setTimeout(() => {
-      elementsToClear.forEach((el) => {
-        el.style.transform = "";
-        el.style.transition = "";
-        el.style.position = "";
-        el.style.left = "";
-        el.style.top = "";
-        el.style.width = "";
-        el.style.height = "";
-        el.style.margin = "";
+      elementsToClear.forEach(({ el, originalCssText }) => {
+        el.style.cssText = originalCssText;
       });
     }, DURATION);
   }