From 395d833dd62e7a02ec7b2f2bf306eff884779fb4 Mon Sep 17 00:00:00 2001
From: Thomas Chandelle <thomas.chandelle@1spatial.com>
Date: Thu, 5 Jan 2017 14:43:54 +0100
Subject: [PATCH 1/2] Constrain the center in zoomByDelta

---
 src/ol/interaction/interaction.js            | 17 ++++++
 test/spec/ol/interaction/interaction.test.js | 63 ++++++++++++++++++++
 2 files changed, 80 insertions(+)

diff --git a/src/ol/interaction/interaction.js b/src/ol/interaction/interaction.js
index 6ce00e740e..ffe39ca86b 100644
--- a/src/ol/interaction/interaction.js
+++ b/src/ol/interaction/interaction.js
@@ -180,6 +180,23 @@ ol.interaction.Interaction.zoom = function(view, resolution, opt_anchor, opt_dur
 ol.interaction.Interaction.zoomByDelta = function(view, delta, opt_anchor, opt_duration) {
   var currentResolution = view.getResolution();
   var resolution = view.constrainResolution(currentResolution, delta, 0);
+
+  // If we have a constraint on center, we need to change the anchor so that the
+  // new center is within the extent. We first calculate the new center, apply
+  // the constraint to it, and then calculate back the anchor
+  if (opt_anchor && resolution !== undefined && resolution !== currentResolution) {
+    var currentCenter = view.getCenter();
+    var center = view.calculateCenterZoom(resolution, opt_anchor);
+    center = view.constrainCenter(center);
+
+    opt_anchor = [
+      (resolution * currentCenter[0] - currentResolution * center[0]) /
+          (resolution - currentResolution),
+      (resolution * currentCenter[1] - currentResolution * center[1]) /
+          (resolution - currentResolution)
+    ];
+  }
+
   ol.interaction.Interaction.zoomWithoutConstraints(
       view, resolution, opt_anchor, opt_duration);
 };
diff --git a/test/spec/ol/interaction/interaction.test.js b/test/spec/ol/interaction/interaction.test.js
index 7c38d9a29f..b9cbf62e01 100644
--- a/test/spec/ol/interaction/interaction.test.js
+++ b/test/spec/ol/interaction/interaction.test.js
@@ -58,4 +58,67 @@ describe('ol.interaction.Interaction', function() {
 
   });
 
+  describe('zoomByDelta()', function() {
+
+    it('changes view resolution', function() {
+      var view = new ol.View({
+        resolution: 1,
+        resolutions: [4, 2, 1, 0.5, 0.25]
+      });
+
+      ol.interaction.Interaction.zoomByDelta(view, 1);
+      expect(view.getResolution()).to.be(0.5);
+
+      ol.interaction.Interaction.zoomByDelta(view, -1);
+      expect(view.getResolution()).to.be(1);
+
+      ol.interaction.Interaction.zoomByDelta(view, 2);
+      expect(view.getResolution()).to.be(0.25);
+
+      ol.interaction.Interaction.zoomByDelta(view, -2);
+      expect(view.getResolution()).to.be(1);
+    });
+
+    it('changes view resolution and center relative to the anchor', function() {
+      var view = new ol.View({
+        center: [0, 0],
+        resolution: 1,
+        resolutions: [4, 2, 1, 0.5, 0.25]
+      });
+
+      ol.interaction.Interaction.zoomByDelta(view, 1, [10, 10]);
+      expect(view.getCenter()).to.eql([5, 5]);
+
+      ol.interaction.Interaction.zoomByDelta(view, -1, [0, 0]);
+      expect(view.getCenter()).to.eql([10, 10]);
+
+      ol.interaction.Interaction.zoomByDelta(view, 2, [0, 0]);
+      expect(view.getCenter()).to.eql([2.5, 2.5]);
+
+      ol.interaction.Interaction.zoomByDelta(view, -2, [0, 0]);
+      expect(view.getCenter()).to.eql([10, 10]);
+    });
+
+    it('changes view resolution and center relative to the anchor, while respecting the extent', function() {
+      var view = new ol.View({
+        center: [0, 0],
+        extent: [-2.5, -2.5, 2.5, 2.5],
+        resolution: 1,
+        resolutions: [4, 2, 1, 0.5, 0.25]
+      });
+
+      ol.interaction.Interaction.zoomByDelta(view, 1, [10, 10]);
+      expect(view.getCenter()).to.eql([2.5, 2.5]);
+
+      ol.interaction.Interaction.zoomByDelta(view, -1, [0, 0]);
+      expect(view.getCenter()).to.eql([2.5, 2.5]);
+
+      ol.interaction.Interaction.zoomByDelta(view, 2, [10, 10]);
+      expect(view.getCenter()).to.eql([2.5, 2.5]);
+
+      ol.interaction.Interaction.zoomByDelta(view, -2, [0, 0]);
+      expect(view.getCenter()).to.eql([2.5, 2.5]);
+    });
+  });
+
 });

From 7f1f3fd6fec3705e6e05110e6dfa66a68963bccf Mon Sep 17 00:00:00 2001
From: Thomas Chandelle <thomas.chandelle@1spatial.com>
Date: Fri, 6 Jan 2017 15:28:38 +0100
Subject: [PATCH 2/2] Constraint center when using trackpad to zoom

---
 src/ol/interaction/mousewheelzoom.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/ol/interaction/mousewheelzoom.js b/src/ol/interaction/mousewheelzoom.js
index 98039aa36e..c4ca25b3fc 100644
--- a/src/ol/interaction/mousewheelzoom.js
+++ b/src/ol/interaction/mousewheelzoom.js
@@ -183,7 +183,7 @@ ol.interaction.MouseWheelZoom.handleEvent = function(mapBrowserEvent) {
     }
     if (this.lastAnchor_) {
       var center = view.calculateCenterZoom(resolution, this.lastAnchor_);
-      view.setCenter(center);
+      view.setCenter(view.constrainCenter(center));
     }
     view.setResolution(resolution);
     if (rebound > 0) {