fix(FlightMap): hide arrows on short legs

Direction arrows could become larger on screen than their underlying
mission legs, obscuring rather than clarifying the route.

They now hide whenever a leg's projected length is shorter than the
30-pixel width of the arrow canvas.

Author: rubenp02

src/FlightMap/MapItems/MapLineArrow.qml

@@ -8,14 +8,18 @@ import QGroundControl.Controls
 import QGroundControl.FlightMap
 
 MapQuickItem {
+    id: root
+
+    required property FlightMap mapControl
+
     property color  arrowColor:     "white"
     property var    fromCoord:      QtPositioning.coordinate()
     property var    toCoord:        QtPositioning.coordinate()
     property int    arrowPosition:  1 ///< 1: first quarter, 2: halfway, 3: last quarter
 
-    property var    _map:           parent
     property real   _arrowSize:     15
     property real   _arrowHeading:  0
+    property real   _screenLegLength: 0
 
     function _updateArrowDetails() {
         if (fromCoord && fromCoord.isValid && toCoord && toCoord.isValid) {
@@ -26,16 +30,38 @@ MapQuickItem {
             coordinate = QtPositioning.coordinate()
             _arrowHeading = 0
         }
+        _updateScreenLegLength()
+    }
+
+    function _updateScreenLegLength() {
+        if (mapControl && fromCoord && fromCoord.isValid && toCoord && toCoord.isValid) {
+            const fromPoint = mapControl.fromCoordinate(fromCoord, false)
+            const toPoint = mapControl.fromCoordinate(toCoord, false)
+            _screenLegLength = Math.hypot(toPoint.x - fromPoint.x, toPoint.y - fromPoint.y)
+        } else {
+            _screenLegLength = 0
+        }
     }
 
     onFromCoordChanged: _updateArrowDetails()
     onToCoordChanged:   _updateArrowDetails()
+    onMapControlChanged: _updateScreenLegLength()
+
+    Component.onCompleted: _updateArrowDetails()
+
+    Connections {
+        target: root.mapControl
+
+        function onCenterChanged() { root._updateScreenLegLength() }
+        function onZoomLevelChanged() { root._updateScreenLegLength() }
+    }
 
     sourceItem: Canvas {
         x:      -_arrowSize
         y:      0
         width:  _arrowSize * 2
         height: _arrowSize
+        visible: root._screenLegLength >= width
 
         onPaint: {
             var ctx = getContext("2d");

src/FlightMap/MapItems/PlanMapItems.qml

@@ -79,6 +79,7 @@ Item {
                     fromCoord:      object ? object.coordinate1 : undefined
                     toCoord:        object ? object.coordinate2 : undefined
                     arrowPosition:  3
+                    mapControl:     _root.map
                     z:              QGroundControl.zOrderWaypointLines + 1
                 }
             }

src/PlanView/PlanView.qml

@@ -349,6 +349,7 @@ Item {
                     fromCoord: object ? object.coordinate1 : undefined
                     toCoord: object ? object.coordinate2 : undefined
                     arrowPosition: 3
+                    mapControl: editorMap
                     z: QGroundControl.zOrderWaypointLines + 1
                 }
             }

src/PlanView/TransectStyleMapVisuals.qml

@@ -136,6 +136,7 @@ Item {
             fromCoord:      _transectPoints[_firstTrueTransectIndex]
             toCoord:        _transectPoints[_firstTrueTransectIndex + 1]
             arrowPosition:  1
+            mapControl:     _root.map
             visible:        _currentItem && !_vertexDrag
             opacity:        _root.opacity
         }
@@ -148,6 +149,7 @@ Item {
             fromCoord:      _transectPoints[nextTrueTransectIndex]
             toCoord:        _transectPoints[nextTrueTransectIndex + 1]
             arrowPosition:  1
+            mapControl:     _root.map
             visible:        _currentItem && _transectCount > 3 && !_vertexDrag
             opacity:        _root.opacity
 
@@ -162,6 +164,7 @@ Item {
             fromCoord:      _transectPoints[_lastTrueTransectIndex - 1]
             toCoord:        _transectPoints[_lastTrueTransectIndex]
             arrowPosition:  3
+            mapControl:     _root.map
             visible:        _currentItem && !_vertexDrag
             opacity:        _root.opacity
         }
@@ -174,6 +177,7 @@ Item {
             fromCoord:      _transectPoints[prevTrueTransectIndex - 1]
             toCoord:        _transectPoints[prevTrueTransectIndex]
             arrowPosition:  13
+            mapControl:     _root.map
             visible:        _currentItem && _transectCount > 3 && !_vertexDrag
             opacity:        _root.opacity