[Example]Add linePattern in line.dart

Author: Kevin Li

example/lib/line.dart

@@ -3,8 +3,10 @@
 // found in the LICENSE file.
 
 import 'dart:async';
+import 'dart:typed_data';
 
 import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
 import 'package:mapbox_gl/mapbox_gl.dart';
 
 import 'main.dart';
@@ -34,6 +36,7 @@ class LineBodyState extends State<LineBody> {
   MapboxMapController? controller;
   int _lineCount = 0;
   Line? _selectedLine;
+  final String _linePatternImage = "assets/fill/cat_silhouette_pattern.png";
 
   void _onMapCreated(MapboxMapController controller) {
     this.controller = controller;
@@ -46,6 +49,13 @@ class LineBodyState extends State<LineBody> {
     super.dispose();
   }
 
+  /// Adds an asset image to the currently displayed style
+  Future<void> addImageFromAsset(String name, String assetName) async {
+    final ByteData bytes = await rootBundle.load(assetName);
+    final Uint8List list = bytes.buffer.asUint8List();
+    return controller!.addImage(name, list);
+  }
+
   _onLineTapped(Line line) async {
     await _updateSelectedLine(
       LineOptions(lineColor: "#ff0000"),
@@ -100,6 +110,14 @@ class LineBodyState extends State<LineBody> {
     });
   }
 
+  Future<void> _changeLinePattern() async {
+    String? current =
+        _selectedLine!.options.linePattern == null ? "assetImage" : null;
+    await _updateSelectedLine(
+      LineOptions(linePattern: current),
+    );
+  }
+
   Future<void> _changeAlpha() async {
     double? current = _selectedLine!.options.lineOpacity;
     if (current == null) {
@@ -124,6 +142,7 @@ class LineBodyState extends State<LineBody> {
   }
 
   _onStyleLoadedCallback() async {
+    addImageFromAsset("assetImage", _linePatternImage);
     await controller!.addLine(
       LineOptions(
         geometry: [LatLng(37.4220, -122.0841), LatLng(37.4240, -122.0941)],
@@ -179,6 +198,12 @@ class LineBodyState extends State<LineBody> {
                                   await _move();
                                 },
                         ),
+                        TextButton(
+                          child: const Text('change line-pattern'),
+                          onPressed: (_selectedLine == null)
+                              ? null
+                              : _changeLinePattern,
+                        ),
                       ],
                     ),
                     Row(