Reader core parity

src/lib/core/reader/zoomHelpers.ts

@@ -0,0 +1,30 @@
+export const ZOOM_MIN = 0.25;
+export const ZOOM_MAX = 4.0;
+export const ZOOM_STEP = 0.1;
+
+/**
+ * Clamp a zoom value between the reader's min/max bounds.
+ */
+export function clampZoom(value: number, min = ZOOM_MIN, max = ZOOM_MAX): number {
+    return Math.max(min, Math.min(max, value));
+}
+
+/**
+ * Return the next zoom level after applying a delta, clamped to valid bounds.
+ * Rounded to avoid floating point drift.
+ */
+export function adjustZoom(current: number, delta: number): number {
+    return clampZoom(Math.round((current + delta) * 1000) / 1000);
+}
+
+/**
+ * Snap to a list of named presets (0.25, 0.5, 0.75, 1.0, 1.5, 2.0, 3.0, 4.0).
+ * Returns the nearest preset value to the given zoom.
+ */
+export const ZOOM_PRESETS = [0.25, 0.5, 0.75, 1.0, 1.5, 2.0, 3.0, 4.0] as const;
+
+export function snapToPreset(value: number): number {
+    return ZOOM_PRESETS.reduce((best, preset) =>
+        Math.abs(preset - value) < Math.abs(best - value) ? preset : best
+    );
+}