add comment for hooks

1 files changed, 38 insertions, 2 deletions

diff --git a/apps/web/src/hooks/use-timeline-playhead.ts b/apps/web/src/hooks/use-timeline-playhead.ts
index 8aee5b1f..de3f8ccf 100644
--- a/apps/web/src/hooks/use-timeline-playhead.ts
+++ b/apps/web/src/hooks/use-timeline-playhead.ts
@@ -11,6 +11,13 @@ interface UseTimelinePlayheadProps {
   rulerScrollRef: React.RefObject<HTMLDivElement>;

 }

 

+/**

+ * useTimelinePlayhead

+ *

+ * Custom hook to manage playhead (scrubbing) logic for a timeline editor.

+ * Handles mouse interaction for timeline ruler, calculates time from mouse,

+ * and enables smooth scrubbing without unnecessary re-renders.

+ */

 export function useTimelinePlayhead({

   currentTime,

   duration,

@@ -19,17 +26,35 @@ export function useTimelinePlayhead({
   rulerRef,

   rulerScrollRef,

 }: UseTimelinePlayheadProps) {

+  // Get current project info (especially FPS) from global store

   const { activeProject } = useProjectStore();

 

+  // Ref to track if currently scrubbing

   const isScrubbingRef = useRef(false);

+

+  // Ref to hold the playhead time while scrubbing (does not trigger re-render)

   const scrubTimeRef = useRef<number | null>(null);

+

+  // State to force re-render when scrubbing ends

   const [_, forceRerender] = useState(0);

 

+  /**

+   * Determines the actual playhead position:

+   * - If scrubbing, use the value in scrubTimeRef

+   * - Otherwise, use the currentTime (controlled by external state)

+   */

   const playheadPosition =

     isScrubbingRef.current && scrubTimeRef.current !== null

       ? scrubTimeRef.current

       : currentTime;

 

+  /**

+   * Calculate timeline time (in seconds) based on mouse X position.

+   * - Gets bounding rect of the ruler

+   * - Adjusts for scroll position if ruler is scrollable

+   * - Converts X pixel offset to seconds using current zoom level

+   * - Snaps to nearest frame using FPS

+   */

   const getTimeFromMouse = useCallback(

     (e: MouseEvent | React.MouseEvent) => {

       const ruler = rulerRef.current;

@@ -43,6 +68,7 @@ export function useTimelinePlayhead({
       const scrollLeft = scrollArea.scrollLeft;

       const x = e.clientX - rect.left + scrollLeft;

 

+      // Calculate how many pixels represent one second, depending on zoom

       const pixelsPerSecond = 50 * zoomLevel;

       const rawTime = Math.max(0, Math.min(duration, x / pixelsPerSecond));

       const time = snapTimeToFrame(rawTime, activeProject?.fps || 30);

@@ -51,6 +77,13 @@ export function useTimelinePlayhead({
     [rulerRef, rulerScrollRef, duration, zoomLevel, activeProject?.fps]

   );

 

+  /**

+   * Handle mouse down event on the ruler:

+   * - Starts scrubbing and updates playhead immediately

+   * - Registers mousemove/mouseup events to allow scrubbing

+   * - Updates time as mouse moves and seeks to new time

+   * - Cleans up listeners and triggers re-render when scrubbing ends

+   */

   const handleRulerMouseDown = useCallback(

     (e: React.MouseEvent) => {

       e.preventDefault();

@@ -61,6 +94,7 @@ export function useTimelinePlayhead({
       scrubTimeRef.current = time;

       seek(time);

 

+      // Mouse move handler: update playhead and seek to new time

       const onMouseMove = (e: MouseEvent) => {

         const t = getTimeFromMouse(e);

         if (t !== scrubTimeRef.current) {

@@ -69,6 +103,7 @@ export function useTimelinePlayhead({
         }

       };

 

+      // Mouse up handler: stop scrubbing, cleanup, and force re-render

       const onMouseUp = () => {

         isScrubbingRef.current = false;

         window.removeEventListener("mousemove", onMouseMove);

@@ -76,6 +111,7 @@ export function useTimelinePlayhead({
         forceRerender((v) => v + 1);

       };

 

+      // Attach listeners to window for drag outside the ruler area

       window.addEventListener("mousemove", onMouseMove);

       window.addEventListener("mouseup", onMouseUp);

     },

@@ -83,7 +119,7 @@ export function useTimelinePlayhead({
   );

 

   return {

-    playheadPosition,

-    handleRulerMouseDown,

+    playheadPosition, // Current playhead position (real-time while scrubbing)

+    handleRulerMouseDown, // Attach to the ruler's onMouseDown

   };

 }