1 files changed, 90 insertions, 0 deletions
diff --git a/apps/web/src/timeline/zoom-utils.ts b/apps/web/src/timeline/zoom-utils.ts
new file mode 100644
index 00000000..39090d92
--- /dev/null
+++ b/apps/web/src/timeline/zoom-utils.ts
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+import {
+	BASE_TIMELINE_PIXELS_PER_SECOND,
+	TIMELINE_ZOOM_MAX,
+} from "@/timeline/scale";
+import { TICKS_PER_SECOND } from "@/wasm";
+
+const PADDING_MAX_RATIO = 0.75;
+const PADDING_MIN_RATIO = 0.15;
+const PADDING_MIN_AT_ZOOM_PERCENT = 0.2;
+
+export function getTimelineZoomMin({
+	duration,
+	containerWidth,
+}: {
+	duration: number;
+	containerWidth: number | null | undefined;
+}): number {
+	const safeDurationSeconds = Math.max(duration / TICKS_PER_SECOND, 1);
+	const safeContainerWidth = containerWidth ?? 1000;
+	const contentRatioAtMinZoom = 1 - PADDING_MAX_RATIO;
+	const availableWidth = safeContainerWidth * contentRatioAtMinZoom;
+	const zoomToFit =
+		availableWidth / (safeDurationSeconds * BASE_TIMELINE_PIXELS_PER_SECOND);
+
+	return Math.min(TIMELINE_ZOOM_MAX, zoomToFit);
+}
+
+export function getTimelinePaddingPx({
+	containerWidth,
+	zoomLevel,
+	minZoom,
+}: {
+	containerWidth: number;
+	zoomLevel: number;
+	minZoom: number;
+}): number {
+	const zoomPercent = getZoomPercent({ zoomLevel, minZoom });
+	const paddingTransitionPercent = Math.min(
+		zoomPercent / PADDING_MIN_AT_ZOOM_PERCENT,
+		1,
+	);
+	const paddingRatio =
+		PADDING_MAX_RATIO -
+		(PADDING_MAX_RATIO - PADDING_MIN_RATIO) * paddingTransitionPercent;
+
+	return containerWidth * paddingRatio;
+}
+
+export function getZoomPercent({
+	zoomLevel,
+	minZoom,
+}: {
+	zoomLevel: number;
+	minZoom: number;
+}): number {
+	return (zoomLevel - minZoom) / (TIMELINE_ZOOM_MAX - minZoom);
+}
+
+/**
+ * convert linear slider position (0-1) to exponential zoom level.
+ * at low slider values, zoom changes are small. at high values, changes are large.
+ */
+export function sliderToZoom({
+	sliderPosition,
+	minZoom,
+	maxZoom = TIMELINE_ZOOM_MAX,
+}: {
+	sliderPosition: number;
+	minZoom: number;
+	maxZoom?: number;
+}): number {
+	const clampedPosition = Math.max(0, Math.min(1, sliderPosition));
+	return minZoom * (maxZoom / minZoom) ** clampedPosition;
+}
+
+/**
+ * convert exponential zoom level to linear slider position (0-1).
+ */
+export function zoomToSlider({
+	zoomLevel,
+	minZoom,
+	maxZoom = TIMELINE_ZOOM_MAX,
+}: {
+	zoomLevel: number;
+	minZoom: number;
+	maxZoom?: number;
+}): number {
+	const clampedZoom = Math.max(minZoom, Math.min(maxZoom, zoomLevel));
+	return Math.log(clampedZoom / minZoom) / Math.log(maxZoom / minZoom);
+}