fix: smooth scrubber end seeking (#386)

* fix: smooth scrubber end seeking

* fix: stop timeline auto-scroll in fit mode

* feat: use percentage-based timeline zoom

* fix: sync timeline playhead on zoom changes

* fix: reset timeline scroll when returning to fit

* fix: keep timeline controls pinned

packages/studio/src/player/components/timelineZoom.test.ts

@@ -0,0 +1,62 @@
+import { describe, expect, it } from "vitest";
+import {
+  clampTimelineZoomPercent,
+  getNextTimelineZoomPercent,
+  getTimelinePixelsPerSecond,
+  getTimelineZoomPercent,
+  MAX_TIMELINE_ZOOM_PERCENT,
+  MIN_TIMELINE_ZOOM_PERCENT,
+} from "./timelineZoom";
+
+describe("clampTimelineZoomPercent", () => {
+  it("defaults invalid values to 100", () => {
+    expect(clampTimelineZoomPercent(Number.NaN)).toBe(100);
+  });
+
+  it("clamps to the supported percent bounds", () => {
+    expect(clampTimelineZoomPercent(1)).toBe(MIN_TIMELINE_ZOOM_PERCENT);
+    expect(clampTimelineZoomPercent(5000)).toBe(MAX_TIMELINE_ZOOM_PERCENT);
+  });
+});
+
+describe("getTimelineZoomPercent", () => {
+  it("treats fit mode as 100 percent", () => {
+    expect(getTimelineZoomPercent("fit", 375)).toBe(100);
+  });
+
+  it("returns the clamped manual zoom percent", () => {
+    expect(getTimelineZoomPercent("manual", 125.2)).toBe(125);
+  });
+});
+
+describe("getTimelinePixelsPerSecond", () => {
+  it("uses fit pixels per second in fit mode", () => {
+    expect(getTimelinePixelsPerSecond(144, "fit", 250)).toBe(144);
+  });
+
+  it("scales from fit pixels per second in manual mode", () => {
+    expect(getTimelinePixelsPerSecond(144, "manual", 125)).toBe(180);
+  });
+});
+
+describe("getNextTimelineZoomPercent", () => {
+  it("zooms out from fit relative to 100 percent", () => {
+    expect(getNextTimelineZoomPercent("out", "fit", 375)).toBe(80);
+  });
+
+  it("zooms in from fit relative to 100 percent", () => {
+    expect(getNextTimelineZoomPercent("in", "fit", 375)).toBe(125);
+  });
+
+  it("clamps the lower bound", () => {
+    expect(getNextTimelineZoomPercent("out", "manual", MIN_TIMELINE_ZOOM_PERCENT)).toBe(
+      MIN_TIMELINE_ZOOM_PERCENT,
+    );
+  });
+
+  it("clamps the upper bound", () => {
+    expect(getNextTimelineZoomPercent("in", "manual", MAX_TIMELINE_ZOOM_PERCENT)).toBe(
+      MAX_TIMELINE_ZOOM_PERCENT,
+    );
+  });
+});