View / apply constraints when an interaction starts

Previously, an interaction could begin while target values
(center/resolution) were out of the allowed range, causing a
glitch where the view zoom/position would jump suddenly.

src/ol/View.js

@@ -1325,10 +1325,14 @@ class View extends BaseObject {
 
   /**
    * Notify the View that an interaction has started.
+   * The view state will be resolved to a stable one if needed
+   * (depending on its constraints).
    * @api
    */
   beginInteraction() {
     this.setHint(ViewHint.INTERACTING, 1);
+
+    this.resolveConstraints(0);
   }
 
   /**

src/ol/control/Zoom.js

@@ -114,6 +114,7 @@ class Zoom extends Control {
       // upon it
       return;
     }
+    view.resolveConstraints(0);
     const currentZoom = view.getZoom();
     if (currentZoom !== undefined) {
       const newZoom = view.getConstrainedZoom(currentZoom + delta);

src/ol/interaction/Interaction.js

@@ -135,6 +135,7 @@ export function zoomByDelta(view, delta, opt_anchor, opt_duration) {
   const newZoom = view.getConstrainedZoom(currentZoom + delta);
   const newResolution = view.getResolutionForZoom(newZoom);
 
+  view.resolveConstraints(0);
   if (view.getAnimating()) {
     view.cancelAnimations();
   }

test/spec/ol/view.test.js

@@ -1801,6 +1801,52 @@ describe('ol.View', function() {
   });
 });
 
+describe('does not start unexpected animations during interaction', function() {
+  let map;
+  beforeEach(function() {
+    map = new Map({
+      target: createMapDiv(512, 256)
+    });
+  });
+  afterEach(function() {
+    disposeMap(map);
+  });
+
+  it('works when initialized with #setCenter() and #setZoom()', function(done) {
+    const view = map.getView();
+    let callCount = 0;
+    view.on('change:resolution', function() {
+      ++callCount;
+    });
+    view.setCenter([0, 0]);
+    view.setZoom(0);
+    view.beginInteraction();
+    view.endInteraction();
+    setTimeout(function() {
+      expect(callCount).to.be(1);
+      done();
+    }, 500);
+  });
+
+  it('works when initialized with #animate()', function(done) {
+    const view = map.getView();
+    let callCount = 0;
+    view.on('change:resolution', function() {
+      ++callCount;
+    });
+    view.animate({
+      center: [0, 0],
+      zoom: 0
+    });
+    view.beginInteraction();
+    view.endInteraction();
+    setTimeout(function() {
+      expect(callCount).to.be(1);
+      done();
+    }, 500);
+  });
+});
+
 describe('ol.View.isNoopAnimation()', function() {
 
   const cases = [{