Refactor constraints static methods to module functions

src/ol/resolutionconstraint.js

@@ -0,0 +1,66 @@
+/**
+ * @module ol/resolutionconstraint
+ */
+import {linearFindNearest} from './array.js';
+import {clamp} from './math.js';
+
+/**
+ * @param {Array.<number>} resolutions Resolutions.
+ * @return {ol.ResolutionConstraintType} Zoom function.
+ */
+export function createSnapToResolutions(resolutions) {
+  return (
+    /**
+     * @param {number|undefined} resolution Resolution.
+     * @param {number} delta Delta.
+     * @param {number} direction Direction.
+     * @return {number|undefined} Resolution.
+     */
+    function(resolution, delta, direction) {
+      if (resolution !== undefined) {
+        let z = linearFindNearest(resolutions, resolution, direction);
+        z = clamp(z + delta, 0, resolutions.length - 1);
+        const index = Math.floor(z);
+        if (z != index && index < resolutions.length - 1) {
+          const power = resolutions[index] / resolutions[index + 1];
+          return resolutions[index] / Math.pow(power, z - index);
+        } else {
+          return resolutions[index];
+        }
+      } else {
+        return undefined;
+      }
+    }
+  );
+}
+
+
+/**
+ * @param {number} power Power.
+ * @param {number} maxResolution Maximum resolution.
+ * @param {number=} opt_maxLevel Maximum level.
+ * @return {ol.ResolutionConstraintType} Zoom function.
+ */
+export function createSnapToPower(power, maxResolution, opt_maxLevel) {
+  return (
+    /**
+     * @param {number|undefined} resolution Resolution.
+     * @param {number} delta Delta.
+     * @param {number} direction Direction.
+     * @return {number|undefined} Resolution.
+     */
+    function(resolution, delta, direction) {
+      if (resolution !== undefined) {
+        const offset = -direction / 2 + 0.5;
+        const oldLevel = Math.floor(
+          Math.log(maxResolution / resolution) / Math.log(power) + offset);
+        let newLevel = Math.max(oldLevel + delta, 0);
+        if (opt_maxLevel !== undefined) {
+          newLevel = Math.min(newLevel, opt_maxLevel);
+        }
+        return maxResolution / Math.pow(power, newLevel);
+      } else {
+        return undefined;
+      }
+    });
+}