feat: pan & zoom motion presets

Ken Burns-style motion effects (zoom in/out, pan left/right/up/down) that
drag onto clips like regular effects. Instead of shader passes they
evaluate a per-frame transform offset in resolveVisualState, so they
stack with keyframed transforms and work in preview and export.

- intensity param (0-100%, keyframable) scales the whole effect
- easing select maps progress through the graph editor's bezier presets
- supportsStandalone: false hides them from effect-track creation
- empty shader pass groups are filtered out so pass-less effects and
  zero-intensity blur no longer crash the compositor

1 files changed, 104 insertions, 2 deletions

diff --git a/apps/web/src/effects/components/assets-view.tsx b/apps/web/src/effects/components/assets-view.tsx
index 000af7e6..8c2ec85b 100644
--- a/apps/web/src/effects/components/assets-view.tsx
+++ b/apps/web/src/effects/components/assets-view.tsx
@@ -53,6 +53,102 @@ function EffectPreviewCanvas({ effectType }: { effectType: string }) {
 	return <canvas ref={canvasRef} className="size-full" />;
 }
 
+const MOTION_ARROW_DIRECTIONS: Record<string, [number, number]> = {
+	"pan-left": [-1, 0],
+	"pan-right": [1, 0],
+	"pan-up": [0, -1],
+	"pan-down": [0, 1],
+};
+
+function drawArrow({
+	context,
+	fromX,
+	fromY,
+	toX,
+	toY,
+}: {
+	context: CanvasRenderingContext2D;
+	fromX: number;
+	fromY: number;
+	toX: number;
+	toY: number;
+}) {
+	const headLength = 10;
+	const angle = Math.atan2(toY - fromY, toX - fromX);
+	context.beginPath();
+	context.moveTo(fromX, fromY);
+	context.lineTo(toX, toY);
+	context.moveTo(toX, toY);
+	context.lineTo(
+		toX - headLength * Math.cos(angle - Math.PI / 6),
+		toY - headLength * Math.sin(angle - Math.PI / 6),
+	);
+	context.moveTo(toX, toY);
+	context.lineTo(
+		toX - headLength * Math.cos(angle + Math.PI / 6),
+		toY - headLength * Math.sin(angle + Math.PI / 6),
+	);
+	context.stroke();
+}
+
+function MotionPreviewCanvas({ effectType }: { effectType: string }) {
+	const canvasRef = useRef<HTMLCanvasElement>(null);
+
+	useEffect(() => {
+		const canvas = canvasRef.current;
+		const context = canvas?.getContext("2d");
+		if (!canvas || !context) return;
+
+		const size = canvas.width;
+		const center = size / 2;
+		context.clearRect(0, 0, size, size);
+		context.fillStyle = "#17171c";
+		context.fillRect(0, 0, size, size);
+		context.strokeStyle = "rgba(255, 255, 255, 0.35)";
+		context.lineWidth = 2;
+		context.strokeRect(size * 0.2, size * 0.28, size * 0.6, size * 0.44);
+		context.strokeStyle = "#ffffff";
+		context.lineWidth = 4;
+		context.lineCap = "round";
+
+		const panDirection = MOTION_ARROW_DIRECTIONS[effectType];
+		if (panDirection) {
+			const [dx, dy] = panDirection;
+			drawArrow({
+				context,
+				fromX: center - dx * size * 0.18,
+				fromY: center - dy * size * 0.18,
+				toX: center + dx * size * 0.18,
+				toY: center + dy * size * 0.18,
+			});
+			return;
+		}
+
+		const inward = effectType === "zoom-out";
+		const spread = size * 0.16;
+		const reach = size * 0.3;
+		for (const [dx, dy] of [
+			[1, 1],
+			[-1, -1],
+		] as const) {
+			const innerX = center + dx * (inward ? reach : spread);
+			const innerY = center + dy * (inward ? reach : spread) * 0.7;
+			const outerX = center + dx * (inward ? spread : reach);
+			const outerY = center + dy * (inward ? spread : reach) * 0.7;
+			drawArrow({ context, fromX: innerX, fromY: innerY, toX: outerX, toY: outerY });
+		}
+	}, [effectType]);
+
+	return (
+		<canvas
+			ref={canvasRef}
+			width={effectPreviewService.PREVIEW_SIZE}
+			height={effectPreviewService.PREVIEW_SIZE}
+			className="size-full"
+		/>
+	);
+}
+
 function EffectItem({ effect }: { effect: EffectDefinition }) {
 	const editor = useEditor();
 
@@ -69,7 +165,11 @@ function EffectItem({ effect }: { effect: EffectDefinition }) {
 		});
 	}, [editor, effect.type]);
 
-	const preview = <EffectPreviewCanvas effectType={effect.type} />;
+	const preview = effect.motion ? (
+		<MotionPreviewCanvas effectType={effect.type} />
+	) : (
+		<EffectPreviewCanvas effectType={effect.type} />
+	);
 
 	return (
 		<DraggableItem
@@ -82,7 +182,9 @@ function EffectItem({ effect }: { effect: EffectDefinition }) {
 				effectType: effect.type,
 				targetElementTypes: EFFECT_TARGET_ELEMENT_TYPES,
 			}}
-			onAddToTimeline={handleAddToTimeline}
+			onAddToTimeline={
+				effect.supportsStandalone === false ? undefined : handleAddToTimeline
+			}
 			aspectRatio={1}
 			isRounded
 			variant="card"