View / add a constrainResolution option

This introduces a breaking change.

This options replaces the various `constrainResolution` options on interactions
and the `fit` method.

Since constraints are now the responsibility of the View, the fact that intermediary
zoom levels are allowed or not is now set in the view options.

By default, the view resolution is unconstrained.

src/ol/View.js

@@ -23,6 +23,7 @@ import {createProjection, METERS_PER_UNIT} from './proj.js';
 import Units from './proj/Units.js';
 import {equals} from './coordinate';
 import {easeOut} from './easing';
+import {createMinMaxResolution} from './resolutionconstraint';
 
 
 /**
@@ -60,9 +61,8 @@ import {easeOut} from './easing';
  * @property {!Array<number>} [padding=[0, 0, 0, 0]] Padding (in pixels) to be
  * cleared inside the view. Values in the array are top, right, bottom and left
  * padding.
- * @property {boolean} [constrainResolution=true] Constrain the resolution.
- * @property {boolean} [nearest=false] If `constrainResolution` is `true`, get
- * the nearest extent instead of the closest that actually fits the view.
+ * @property {boolean} [nearest=false] If the view `constrainResolution` option is `true`,
+ * get the nearest extent instead of the closest that actually fits the view.
  * @property {number} [minResolution=0] Minimum resolution that we zoom to.
  * @property {number} [maxZoom] Maximum zoom level that we zoom to. If
  * `minResolution` is given, this property is ignored.
@@ -120,6 +120,9 @@ import {easeOut} from './easing';
  * resolution constraint. It is used together with `maxZoom` (or
  * `minResolution`) and `zoomFactor`.  Note that if `maxResolution` is also
  * provided, it is given precedence over `minZoom`.
+ * @property {boolean} [constrainResolution] If true, the view will always
+ * animate to the closest zoom level after an interaction; false means
+ * intermediary zoom levels are allowed. Default is false.
  * @property {import("./proj.js").ProjectionLike} [projection='EPSG:3857'] The
  * projection. The default is Spherical Mercator.
  * @property {number} [resolution] The initial resolution for the view. The
@@ -621,7 +624,7 @@ class View extends BaseObject {
     }
 
     if (!this.getAnimating()) {
-      this.resolveConstraints_();
+      setTimeout(this.resolveConstraints_.bind(this), 0);
     }
   }
 
@@ -790,6 +793,15 @@ class View extends BaseObject {
     this.applyOptions_(this.getUpdatedOptions_({minZoom: zoom}));
   }
 
+  /**
+   * Set whether the view shoud allow intermediary zoom levels.
+   * @param {boolean} enabled Whether the resolution is constrained.
+   * @api
+   */
+  setConstrainResolution(enabled) {
+    this.applyOptions_(this.getUpdatedOptions_({constrainResolution: enabled}));
+  }
+
   /**
    * Get the view projection.
    * @return {import("./proj/Projection.js").default} The projection of the view.
@@ -1001,8 +1013,6 @@ class View extends BaseObject {
     }
 
     const padding = options.padding !== undefined ? options.padding : [0, 0, 0, 0];
-    const constrainResolution = options.constrainResolution !== undefined ?
-      options.constrainResolution : true;
     const nearest = options.nearest !== undefined ? options.nearest : false;
     let minResolution;
     if (options.minResolution !== undefined) {
@@ -1038,9 +1048,7 @@ class View extends BaseObject {
       [size[0] - padding[1] - padding[3], size[1] - padding[0] - padding[2]]);
     resolution = isNaN(resolution) ? minResolution :
       Math.max(resolution, minResolution);
-    if (constrainResolution) {
-      resolution = this.getValidResolution(resolution, nearest ? 0 : 1);
-    }
+    resolution = this.getValidResolution(resolution, nearest ? 0 : 1);
 
     // calculate center
     sinAngle = -sinAngle; // go back to original rotation
@@ -1346,8 +1354,14 @@ export function createResolutionConstraint(options) {
     maxResolution = resolutions[minZoom];
     minResolution = resolutions[maxZoom] !== undefined ?
       resolutions[maxZoom] : resolutions[resolutions.length - 1];
-    resolutionConstraint = createSnapToResolutions(resolutions,
-      !options.constrainOnlyCenter && options.extent);
+
+    if (options.constrainResolution) {
+      resolutionConstraint = createSnapToResolutions(resolutions,
+        !options.constrainOnlyCenter && options.extent);
+    } else {
+      resolutionConstraint = createMinMaxResolution(maxResolution, minResolution,
+        !options.constrainOnlyCenter && options.extent);
+    }
   } else {
     // calculate the default min and max resolution
     const projection = createProjection(options.projection, 'EPSG:3857');
@@ -1391,9 +1405,14 @@ export function createResolutionConstraint(options) {
       Math.log(maxResolution / minResolution) / Math.log(zoomFactor));
     minResolution = maxResolution / Math.pow(zoomFactor, maxZoom - minZoom);
 
-    resolutionConstraint = createSnapToPower(
-      zoomFactor, maxResolution, minResolution,
-      !options.constrainOnlyCenter && options.extent);
+    if (options.constrainResolution) {
+      resolutionConstraint = createSnapToPower(
+        zoomFactor, maxResolution, minResolution,
+        !options.constrainOnlyCenter && options.extent);
+    } else {
+      resolutionConstraint = createMinMaxResolution(maxResolution, minResolution,
+        !options.constrainOnlyCenter && options.extent);
+    }
   }
   return {constraint: resolutionConstraint, maxResolution: maxResolution,
     minResolution: minResolution, minZoom: minZoom, zoomFactor: zoomFactor};