import'dart:ui';
import'package:flutter/material.dart';
import'package:flutter_colorpicker/flutter_colorpicker.dart';
voidmain() =>runApp(constMyApp());
classMyAppextendsStatelessWidget {
constMyApp({super.key});
@overrideWidgetbuild(BuildContextcontext) {
returnconstMaterialApp(
home: DrawingBoard(),
    );
  }
}
/// 画板应用的主页 [StatefulWidget]。classDrawingBoardextendsStatefulWidget {
constDrawingBoard({super.key});
@overrideState<DrawingBoard>createState() =>_DrawingBoardState();
}
/// [DrawingBoard] 的状态类，负责管理用户绘制的功能和界面。class_DrawingBoardStateextendsState<DrawingBoard> {
List<DrawObject>drawObjects= [];
ColorselectedColor=Colors.black;
boolisFirstDraw=true;
/// 显示颜色选择对话框的方法。voidselectColor() {
showDialog(
context: context,
builder: (BuildContextcontext) {
ColornewColor=selectedColor;
returnAlertDialog(
title: constText('选择颜色'),
content: SingleChildScrollView(
child: ColorPicker(
pickerColor: selectedColor,
onColorChanged: (color) {
newColor=color;
              },
            ),
          ),
actions: <Widget>[
TextButton(
onPressed: () {
setState(() {
selectedColor=newColor;
                });
Navigator.of(context).pop();
              },
child: constText('确定'),
            ),
          ],
        );
      },
    );
  }
@overrideWidgetbuild(BuildContextcontext) {
// 创建一个鼠标光标，使用Icons.draw_outlined图标constmouseCursor=SystemMouseCursors.click;
returnScaffold(
appBar: AppBar(
title: constText('Jack Lee 的画板'),
actions: [
IconButton(
icon: constIcon(Icons.color_lens),
onPressed: () {
selectColor();
            },
          ),
        ],
      ),
body: MouseRegion(
cursor: mouseCursor, // 使用自定义光标child: GestureDetector(
onPanUpdate: (details) {
setState(() {
RenderBoxrenderBox=context.findRenderObject() asRenderBox;
finaloffset=renderBox.globalToLocal(details.localPosition);
if (isFirstDraw) {
drawObjects.add(DrawObject([], selectedColor));
isFirstDraw=false;
              }
if (drawObjects.isNotEmpty) {
drawObjects.last.points.add(offset);
              }
            });
          },
onPanEnd: (details) {
setState(() {
drawObjects.add(DrawObject([], selectedColor));
isFirstDraw=true;
            });
          },
child: CustomPaint(
painter: MyPainter(drawObjects),
size: Size.infinite,
          ),
        ),
      ),
    );
  }
}
/// 自定义画板的绘制器 [CustomPainter]。classMyPainterextendsCustomPainter {
finalList<DrawObject>drawObjects;
MyPainter(this.drawObjects);
@overridevoidpaint(Canvascanvas, Sizesize) {
for (finaldrawObjectindrawObjects) {
finalpaint=Paint()
        ..color=drawObject.color        ..strokeCap=StrokeCap.round        ..strokeWidth=5.0;
if (drawObject.points.length>1) {
for (inti=0; i<drawObject.points.length-1; i++) {
if (drawObject.points[i] !=null&&drawObject.points[i+1] !=null) {
canvas.drawLine(
drawObject.points[i]!, drawObject.points[i+1]!, paint);
          }
        }
      } elseif (drawObject.points.isNotEmpty) {
canvas.drawPoints(
PointMode.points, drawObject.points.cast<Offset>(), paint);
      }
    }
  }
@overrideboolshouldRepaint(CustomPainteroldDelegate) {
returntrue;
  }
}
/// 用户绘制的对象类，包括点和颜色。classDrawObject {
finalList<Offset?>points;
finalColorcolor;
DrawObject(this.points, this.color);
}