From f1043734438c8518a302f698d9ae6583a75f0c14 Mon Sep 17 00:00:00 2001
From: cashmere <cashmere@autistici.org>
Date: Sun, 16 Aug 2026 06:16:56 +0200
Subject: feat: add transitions, track mixing, and voiceover controls

---
 apps/web/src/timeline/components/drop-target.ts | 90 +++++++++++++++++++++++--
 1 file changed, 85 insertions(+), 5 deletions(-)

(limited to 'apps/web/src/timeline/components/drop-target.ts')

diff --git a/apps/web/src/timeline/components/drop-target.ts b/apps/web/src/timeline/components/drop-target.ts
index f68a4b72..e22c8af9 100644
--- a/apps/web/src/timeline/components/drop-target.ts
+++ b/apps/web/src/timeline/components/drop-target.ts
@@ -1,5 +1,9 @@
-import type { TimelineTrack, TimelineElement } from "@/timeline";
-import type { ComputeDropTargetParams, DropTarget } from "@/timeline";
+import type {
+	ComputeDropTargetParams,
+	DropTarget,
+	TimelineElement,
+	TimelineTrack,
+} from "@/timeline";
 import { resolveTrackPlacement } from "@/timeline/placement";
 import { TIMELINE_TRACK_GAP_PX } from "./layout";
 import { getTrackHeight } from "./track-layout";
@@ -97,6 +101,71 @@ function fallbackNewTrackDropTarget({
 		insertPosition: null,
 		xPosition,
 		targetElement: EMPTY_TARGET_ELEMENT,
+		targetCut: null,
+	};
+}
+
+export function computeTransitionCutDropTarget({
+	mouseX,
+	mouseY,
+	tracks,
+	pixelsPerSecond,
+	zoomLevel,
+}: {
+	mouseX: number;
+	mouseY: number;
+	tracks: ComputeDropTargetParams["tracks"];
+	pixelsPerSecond: number;
+	zoomLevel: number;
+}): DropTarget | null {
+	const orderedTracks = [...tracks.overlay, tracks.main, ...tracks.audio];
+	const trackAtMouse = getTrackAtY({ mouseY, tracks: orderedTracks });
+	if (!trackAtMouse) return null;
+
+	const track = orderedTracks[trackAtMouse.trackIndex];
+	if (!track || track.type !== "video") return null;
+
+	const elements = track.elements
+		.filter((element) => element.type === "video" || element.type === "image")
+		.slice()
+		.sort((left, right) => left.startTime - right.startTime);
+	let nearest: {
+		outgoingElementId: string;
+		incomingElementId: string;
+		time: MediaTime;
+		distance: number;
+	} | null = null;
+
+	for (let index = 1; index < elements.length; index += 1) {
+		const outgoing = elements[index - 1];
+		const incoming = elements[index];
+		const cutTime = incoming.startTime;
+		if (outgoing.startTime + outgoing.duration !== cutTime) continue;
+
+		const cutX = (cutTime / TICKS_PER_SECOND) * pixelsPerSecond * zoomLevel;
+		const distance = Math.abs(mouseX - cutX);
+		if (distance > 12 || (nearest && nearest.distance <= distance)) continue;
+		nearest = {
+			outgoingElementId: outgoing.id,
+			incomingElementId: incoming.id,
+			time: cutTime,
+			distance,
+		};
+	}
+
+	if (!nearest) return null;
+	return {
+		trackIndex: trackAtMouse.trackIndex,
+		isNewTrack: false,
+		insertPosition: null,
+		xPosition: nearest.time,
+		targetElement: null,
+		targetCut: {
+			trackId: track.id,
+			outgoingElementId: nearest.outgoingElementId,
+			incomingElementId: nearest.incomingElementId,
+			time: nearest.time,
+		},
 	};
 }
 
@@ -133,7 +202,9 @@ export function computeDropTarget({
 		const placementResult = resolveTrackPlacement({
 			tracks,
 			elementType,
-			timeSpans: [{ startTime: xPosition, duration: elementDuration, excludeElementId }],
+			timeSpans: [
+				{ startTime: xPosition, duration: elementDuration, excludeElementId },
+			],
 			strategy: {
 				type: "preferIndex",
 				trackIndex: 0,
@@ -153,6 +224,7 @@ export function computeDropTarget({
 			insertPosition: emptyTimelineResult.insertPosition,
 			xPosition,
 			targetElement: EMPTY_TARGET_ELEMENT,
+			targetCut: null,
 		};
 	}
 
@@ -168,7 +240,9 @@ export function computeDropTarget({
 		const placementResult = resolveTrackPlacement({
 			tracks,
 			elementType,
-			timeSpans: [{ startTime: xPosition, duration: elementDuration, excludeElementId }],
+			timeSpans: [
+				{ startTime: xPosition, duration: elementDuration, excludeElementId },
+			],
 			strategy: {
 				type: "preferIndex",
 				trackIndex: isAboveAllTracks ? 0 : orderedTracks.length - 1,
@@ -188,6 +262,7 @@ export function computeDropTarget({
 			insertPosition: outOfBoundsResult.insertPosition,
 			xPosition,
 			targetElement: EMPTY_TARGET_ELEMENT,
+			targetCut: null,
 		};
 	}
 
@@ -210,6 +285,7 @@ export function computeDropTarget({
 				insertPosition: null,
 				xPosition,
 				targetElement,
+				targetCut: null,
 			};
 		}
 	}
@@ -218,7 +294,9 @@ export function computeDropTarget({
 	const placementResult = resolveTrackPlacement({
 		tracks,
 		elementType,
-		timeSpans: [{ startTime: xPosition, duration: elementDuration, excludeElementId }],
+		timeSpans: [
+			{ startTime: xPosition, duration: elementDuration, excludeElementId },
+		],
 		strategy: {
 			type: "preferIndex",
 			trackIndex,
@@ -242,6 +320,7 @@ export function computeDropTarget({
 			insertPosition: null,
 			xPosition: adjustedXPosition,
 			targetElement: EMPTY_TARGET_ELEMENT,
+			targetCut: null,
 		};
 	}
 
@@ -251,6 +330,7 @@ export function computeDropTarget({
 		insertPosition: placementResult.insertPosition,
 		xPosition,
 		targetElement: EMPTY_TARGET_ELEMENT,
+		targetCut: null,
 	};
 }
 
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