feat(studio): scale GSAP positions on clip resize + shift on drag + diamond fixes (#1448)

Resize: proportionally scale all GSAP animation positions and durations
to fit the new clip duration via scalePositionsInScript. This preserves
clip-relative keyframe percentages — diamonds don't move during resize,
nothing disappears. Modeled after After Effects Time Stretch behavior.

Drag: shift all GSAP positions by the time delta (unchanged from before).

Diamond rendering:
- Clamp diamonds at 0%/100% so they stay fully visible at clip edges
- Filter out-of-range keyframes using predicted percentages during resize
- Clamp connection lines to clip boundaries
- PropertyRows: same edge clamping for SVG diamonds

Parser: scalePositionsInScript (proportional position + duration scaling),
shiftPositionsInScript (rigid shift), scale-positions + shift-positions
mutation types, 5 shift tests passing.

packages/core/src/parsers/gsapParser.test.ts

@@ -19,6 +19,8 @@ import {
   addAnimationWithKeyframesToScript,
   splitAnimationsInScript,
   splitIntoPropertyGroups,
+  shiftPositionsInScript,
+  scalePositionsInScript,
 } from "./gsapParser.js";
 import type { GsapAnimation } from "./gsapParser.js";
 import { classifyPropertyGroup, classifyTweenPropertyGroup } from "./gsapConstants.js";
@@ -2275,3 +2277,113 @@ describe("splitIntoPropertyGroups", () => {
     }
   });
 });
+
+describe("shiftPositionsInScript", () => {
+  it("shifts all numeric positions for the target selector", () => {
+    const script = `const tl = gsap.timeline({ paused: true });
+tl.from("#hero", { opacity: 0, duration: 1 }, 0);
+tl.to("#hero", { opacity: 0, duration: 0.5 }, 2.5);
+tl.from("#bg", { scale: 0, duration: 1 }, 1);`;
+    const result = shiftPositionsInScript(script, "#hero", 3);
+    const parsed = parseGsapScript(result);
+    const hero = parsed.animations.filter((a) => a.targetSelector === "#hero");
+    expect(hero[0].position).toBe(3);
+    expect(hero[1].position).toBe(5.5);
+    const bg = parsed.animations.find((a) => a.targetSelector === "#bg");
+    expect(bg!.position).toBe(1);
+  });
+
+  it("clamps negative-going positions to zero", () => {
+    const script = `const tl = gsap.timeline({ paused: true });
+tl.to("#el", { x: 100, duration: 1 }, 0.3);
+tl.to("#el", { y: 50, duration: 1 }, 1.5);`;
+    const result = shiftPositionsInScript(script, "#el", -1.0);
+    const parsed = parseGsapScript(result);
+    const anims = parsed.animations.filter((a) => a.targetSelector === "#el");
+    expect(anims[0].position).toBe(0);
+    expect(anims[1].position).toBe(0.5);
+  });
+
+  it("returns the original script when delta is zero", () => {
+    const script = `const tl = gsap.timeline({ paused: true });
+tl.to("#el", { x: 100, duration: 1 }, 2);`;
+    expect(shiftPositionsInScript(script, "#el", 0)).toBe(script);
+  });
+
+  it("does not collide when two tweens have adjacent positions", () => {
+    const script = `const tl = gsap.timeline({ paused: true });
+tl.to("#burst", { opacity: 1, duration: 0.5 }, 1.0);
+tl.to("#burst", { opacity: 0, duration: 0.5 }, 1.5);`;
+    const result = shiftPositionsInScript(script, "#burst", 0.5);
+    const parsed = parseGsapScript(result);
+    const burst = parsed.animations.filter((a) => a.targetSelector === "#burst");
+    expect(burst[0].position).toBe(1.5);
+    expect(burst[1].position).toBe(2);
+  });
+
+  it("skips string positions", () => {
+    const script = `const tl = gsap.timeline({ paused: true });
+tl.to("#el", { x: 100, duration: 1 }, 2);
+tl.to("#el", { y: 50, duration: 1 }, "+=0.5");`;
+    const result = shiftPositionsInScript(script, "#el", 1);
+    const parsed = parseGsapScript(result);
+    expect(parsed.animations[0].position).toBe(3);
+    expect(parsed.animations[1].position).toBe("+=0.5");
+  });
+});
+
+describe("scalePositionsInScript", () => {
+  it("scales positions and durations proportionally for the target selector", () => {
+    const script = `const tl = gsap.timeline({ paused: true });
+tl.from("#hero", { opacity: 0, duration: 1 }, 0);
+tl.to("#hero", { opacity: 0, duration: 0.5 }, 2.5);
+tl.from("#bg", { scale: 0, duration: 1 }, 1);`;
+    const result = scalePositionsInScript(script, "#hero", 0, 3, 0, 2);
+    const parsed = parseGsapScript(result);
+    const hero = parsed.animations.filter((a) => a.targetSelector === "#hero");
+    expect(hero[0].position).toBe(0);
+    expect(hero[0].duration).toBeCloseTo(0.667, 2);
+    expect(hero[1].position).toBeCloseTo(1.667, 2);
+    expect(hero[1].duration).toBeCloseTo(0.333, 2);
+    const bg = parsed.animations.find((a) => a.targetSelector === "#bg");
+    expect(bg!.position).toBe(1);
+    expect(bg!.duration).toBe(1);
+  });
+
+  it("handles start-edge resize (new start + shorter duration)", () => {
+    const script = `const tl = gsap.timeline({ paused: true });
+tl.from("#el", { opacity: 0, duration: 1 }, 0);
+tl.to("#el", { y: 50, duration: 0.5 }, 2.5);`;
+    const result = scalePositionsInScript(script, "#el", 0, 3, 1, 2);
+    const parsed = parseGsapScript(result);
+    const anims = parsed.animations.filter((a) => a.targetSelector === "#el");
+    expect(anims[0].position).toBe(1);
+    expect(anims[0].duration).toBeCloseTo(0.667, 2);
+    expect(anims[1].position).toBeCloseTo(2.667, 2);
+    expect(anims[1].duration).toBeCloseTo(0.333, 2);
+  });
+
+  it("clamps negative-going positions to zero", () => {
+    const script = `const tl = gsap.timeline({ paused: true });
+tl.to("#el", { x: 100, duration: 1 }, 2);`;
+    const result = scalePositionsInScript(script, "#el", 2, 1, 0, 0.5);
+    const parsed = parseGsapScript(result);
+    expect(parsed.animations[0].position).toBe(0);
+  });
+
+  it("returns the original script when old and new timing are identical", () => {
+    const script = `const tl = gsap.timeline({ paused: true });
+tl.to("#el", { x: 100, duration: 1 }, 2);`;
+    expect(scalePositionsInScript(script, "#el", 0, 3, 0, 3)).toBe(script);
+  });
+
+  it("skips string positions", () => {
+    const script = `const tl = gsap.timeline({ paused: true });
+tl.to("#el", { x: 100, duration: 1 }, 2);
+tl.to("#el", { y: 50, duration: 1 }, "+=0.5");`;
+    const result = scalePositionsInScript(script, "#el", 0, 3, 0, 2);
+    const parsed = parseGsapScript(result);
+    expect(parsed.animations[0].position).toBeCloseTo(1.333, 2);
+    expect(parsed.animations[1].position).toBe("+=0.5");
+  });
+});

packages/core/src/parsers/gsapParser.ts

@@ -1322,6 +1322,67 @@ export function updateAnimationInScript(
   return recast.print(parsed.ast).code;
 }
 
+export function shiftPositionsInScript(
+  script: string,
+  targetSelector: string,
+  delta: number,
+): string {
+  let parsed: ParsedGsapAst;
+  try {
+    parsed = parseGsapAst(script);
+  } catch (e) {
+    console.warn("[gsap-parser] shiftPositionsInScript parse failed:", e);
+    return script;
+  }
+  let changed = false;
+  for (const entry of parsed.located) {
+    if (entry.animation.targetSelector !== targetSelector) continue;
+    if (typeof entry.animation.position !== "number") continue;
+    const newPos = Math.max(0, Math.round((entry.animation.position + delta) * 1000) / 1000);
+    applyUpdatesToCall(entry.call, { position: newPos });
+    changed = true;
+  }
+  return changed ? recast.print(parsed.ast).code : script;
+}
+
+export function scalePositionsInScript(
+  script: string,
+  targetSelector: string,
+  oldStart: number,
+  oldDuration: number,
+  newStart: number,
+  newDuration: number,
+): string {
+  if (oldDuration <= 0 || newDuration <= 0) return script;
+  const ratio = newDuration / oldDuration;
+  let parsed: ParsedGsapAst;
+  try {
+    parsed = parseGsapAst(script);
+  } catch (e) {
+    console.warn("[gsap-parser] scalePositionsInScript parse failed:", e);
+    return script;
+  }
+  let changed = false;
+  for (const entry of parsed.located) {
+    if (entry.animation.targetSelector !== targetSelector) continue;
+    if (typeof entry.animation.position !== "number") continue;
+    const newPos = Math.max(
+      0,
+      Math.round((newStart + (entry.animation.position - oldStart) * ratio) * 1000) / 1000,
+    );
+    const updates: Partial<GsapAnimation> = { position: newPos };
+    if (typeof entry.animation.duration === "number" && entry.animation.duration > 0) {
+      updates.duration = Math.max(
+        0.001,
+        Math.round(entry.animation.duration * ratio * 1000) / 1000,
+      );
+    }
+    applyUpdatesToCall(entry.call, updates);
+    changed = true;
+  }
+  return changed ? recast.print(parsed.ast).code : script;
+}
+
 function updateAnimationSelector(script: string, animationId: string, newSelector: string): string {
   let parsed: ParsedGsapAst;
   try {

packages/core/src/studio-api/routes/files.ts

@@ -466,6 +466,19 @@ type GsapMutationRequest =
   | {
       type: "delete-all-for-selector";
       targetSelector: string;
+    }
+  | {
+      type: "shift-positions";
+      targetSelector: string;
+      delta: number;
+    }
+  | {
+      type: "scale-positions";
+      targetSelector: string;
+      oldStart: number;
+      oldDuration: number;
+      newStart: number;
+      newDuration: number;
     };
 
 // ── GSAP mutation executor ──────────────────────────────────────────────────
@@ -715,6 +728,35 @@ async function executeGsapMutation(
       const result = splitIntoPropertyGroups(block.scriptText, body.animationId);
       return result.script;
     }
+    case "shift-positions": {
+      const { targetSelector, delta } = body;
+      if (!targetSelector || !Number.isFinite(delta) || delta === 0) return block.scriptText;
+      const { shiftPositionsInScript } = parser;
+      return shiftPositionsInScript(block.scriptText, targetSelector, delta);
+    }
+    case "scale-positions": {
+      const { targetSelector, oldStart, oldDuration, newStart, newDuration } = body;
+      if (
+        !targetSelector ||
+        !Number.isFinite(oldStart) ||
+        !Number.isFinite(oldDuration) ||
+        !Number.isFinite(newStart) ||
+        !Number.isFinite(newDuration) ||
+        oldDuration <= 0 ||
+        newDuration <= 0
+      )
+        return block.scriptText;
+      if (oldStart === newStart && oldDuration === newDuration) return block.scriptText;
+      const { scalePositionsInScript } = parser;
+      return scalePositionsInScript(
+        block.scriptText,
+        targetSelector,
+        oldStart,
+        oldDuration,
+        newStart,
+        newDuration,
+      );
+    }
     default:
       return respond({ error: `unknown mutation type: ${(body as { type: string }).type}` }, 400);
   }