From f3ce8e23b47cc98da0472303c62b2f3568b5a568 Mon Sep 17 00:00:00 2001
From: Andreas Hocevar <andreas.hocevar@gmail.com>
Date: Fri, 14 Feb 2020 13:49:08 +0100
Subject: [PATCH] Fractional zoom changes in WHEEL mode

---
 src/ol/interaction/MouseWheelZoom.js            | 15 +++++++++++----
 test/spec/ol/interaction/mousewheelzoom.test.js |  4 ++--
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/src/ol/interaction/MouseWheelZoom.js b/src/ol/interaction/MouseWheelZoom.js
index 1ed762bc17..92c57b1ad7 100644
--- a/src/ol/interaction/MouseWheelZoom.js
+++ b/src/ol/interaction/MouseWheelZoom.js
@@ -130,7 +130,7 @@ class MouseWheelZoom extends Interaction {
      * @private
      * @type {number}
      */
-    this.trackpadDeltaPerZoom_ = 300;
+    this.deltaPerZoom_ = 300;
 
   }
 
@@ -220,7 +220,7 @@ class MouseWheelZoom extends Interaction {
         view.beginInteraction();
       }
       this.trackpadTimeoutId_ = setTimeout(this.endInteraction_.bind(this), this.trackpadEventGap_);
-      view.adjustZoom(-delta / this.trackpadDeltaPerZoom_, this.lastAnchor_);
+      view.adjustZoom(-delta / this.deltaPerZoom_, this.lastAnchor_);
       this.startTime_ = now;
       return false;
     }
@@ -244,8 +244,15 @@ class MouseWheelZoom extends Interaction {
     if (view.getAnimating()) {
       view.cancelAnimations();
     }
-    const delta = clamp(this.totalDelta_, -this.maxDelta_, this.maxDelta_);
-    zoomByDelta(view, -delta, this.lastAnchor_, this.duration_);
+    let delta = -clamp(this.totalDelta_, -this.maxDelta_ * this.deltaPerZoom_, this.maxDelta_ * this.deltaPerZoom_) / this.deltaPerZoom_;
+    const currentZoom = view.getZoom();
+    const newZoom = view.getConstrainedZoom(currentZoom + delta);
+    if (currentZoom === newZoom) {
+      // view has a zoom constraint, zoom by 1
+      delta = delta ? delta > 0 ? 1 : -1 : 0;
+    }
+    zoomByDelta(view, delta, this.lastAnchor_, this.duration_);
+
     this.mode_ = undefined;
     this.totalDelta_ = 0;
     this.lastAnchor_ = null;
diff --git a/test/spec/ol/interaction/mousewheelzoom.test.js b/test/spec/ol/interaction/mousewheelzoom.test.js
index ee1858bf5d..8f0343446d 100644
--- a/test/spec/ol/interaction/mousewheelzoom.test.js
+++ b/test/spec/ol/interaction/mousewheelzoom.test.js
@@ -121,7 +121,7 @@ describe('ol.interaction.MouseWheelZoom', function() {
         const event = new MapBrowserEvent('wheel', map, {
           type: 'wheel',
           deltaMode: WheelEvent.DOM_DELTA_LINE,
-          deltaY: 3.714599609375,
+          deltaY: 20,
           target: map.getViewport(),
           preventDefault: Event.prototype.preventDefault
         });
@@ -140,7 +140,7 @@ describe('ol.interaction.MouseWheelZoom', function() {
 
         const event = new MapBrowserEvent('wheel', map, {
           type: 'wheel',
-          deltaY: 120,
+          deltaY: 300,
           target: map.getViewport(),
           preventDefault: Event.prototype.preventDefault
         });