Avoid accidental zooms while drawing beeline

js/util/ClickTolerantBoxZoom.js

@@ -0,0 +1,55 @@
+/**
+ * Avoids conflict between shift-click and shift-drag.
+ * Extends BoxZoom to support a small click tolerance like in Draggable and
+ * a larger drag tolerance as a "neutral zone" before starting with box zoom dragging,
+ * to avoid accidental zooms.
+ */
+BR.ClickTolerantBoxZoom = L.Map.BoxZoom.extend({
+    clickTolerance: L.Draggable.prototype.options.clickTolerance,
+    // use more than clickTolerance before starting box zoom to surely avoid accidental zooms
+    dragTolerance: 15,
+    // flag to enable or disable click/drag tolerance, classic BoxZoom behaviour when false
+    tolerant: true,
+
+    // "neutral zone", state between clickTolerance and dragTolerance,
+    // already signals dragging to map and thus prevents click
+    _preMoved: false,
+
+    moved: function () {
+        return this._preMoved || this._moved;
+    },
+
+    _resetState: function () {
+        L.Map.BoxZoom.prototype._resetState.call(this);
+        this._preMoved = false;
+    },
+
+    _onMouseMove: function (e) {
+        if (!this._moved) {
+            const point = this._map.mouseEventToContainerPoint(e);
+
+            // derived from L.Draggable._onMove
+            var offsetPoint = point.clone()._subtract(this._startPoint);
+            var offset = Math.abs(offsetPoint.x || 0) + Math.abs(offsetPoint.y || 0);
+
+            if (this.tolerant && offset < this.dragTolerance) {
+                if (!this._preMoved && offset >= this.clickTolerance) {
+                    this._preMoved = true;
+                }
+
+                return;
+            }
+        }
+
+        L.Map.BoxZoom.prototype._onMouseMove.call(this, e);
+    },
+
+    _onMouseUp: function (e) {
+        L.Map.BoxZoom.prototype._onMouseUp.call(this, e);
+
+        if (!this._moved && this._preMoved) {
+            this._clearDeferredResetState();
+            this._resetStateTimeout = setTimeout(L.Util.bind(this._resetState, this), 0);
+        }
+    },
+});