之前做了一个Android的颜色选择器，不过没开源，闲暇时间做了个flutter颜色选择器，废话不多说先看效果：

                                                   

这个可以显示任意位置，大小，但是大小不能超过屏幕。

直接上代码吧：

import 'package:flutter/material.dart';
import 'package:flutter/widgets.dart';
import 'dart:math';

typedef SelectColor = Color Function(Color color);

class ColorPickView extends StatefulWidget {
  Size size;
  double selectRadius;
  double padding;
  Color selectColor;
  Color selectRingColor;
  final SelectColor selectColorCallBack;

  ColorPickView(
      {this.size,
      this.selectColorCallBack,
      this.selectRadius,
      this.padding,
      this.selectRingColor,
      this.selectColor}) {
    assert(size == null || (size != null && size.height == size.width),
        '控件宽高必须相等');
  }

  @override
  State<StatefulWidget> createState() {
    return ColorPickState();
  }
}

class ColorPickState extends State<ColorPickView> {
  double radius;
  Color currentColor = Color(0xff00ff);
  Offset currentOffset;
  Offset topLeftPosition;
  Offset selectPosition;
  Size screenSize;
  GlobalKey globalKey = new GlobalKey();
  bool isTap = false;

  @override
  Widget build(BuildContext context) {
    screenSize ??= MediaQuery.of(context).size;
    widget.size ??= screenSize;
    widget.selectRadius ??= 10;
    widget.padding ??= 40;
    widget.selectRingColor ??= Colors.black;
    assert(
        widget.size == null ||
            (widget.size != null && screenSize.width >= widget.size.width),
        '控件宽度太宽');
    radius = widget.size.width / 2 - widget.padding;
    currentOffset ??= Offset(radius, radius);
    if (widget.selectColor != null && selectPosition == null)
      _setColor(widget.selectColor);
    _initLeftTop();
    return GestureDetector(
      key: globalKey,
      child: Container(
        width: widget.size.width,
        height: widget.size.width,
        child: Stack(
          alignment: Alignment.center,
          children: <Widget>[
            CustomPaint(
              painter: ColorPick(radius: radius),
              size: widget.size,
            ),
            Positioned(
              left: isTap
                  ? currentOffset.dx -
                      (topLeftPosition == null ? 0 : (topLeftPosition.dx+widget.selectRadius/2))
                  : (selectPosition == null ? radius : selectPosition.dx+widget.selectRadius/2),
              top: isTap
                  ? currentOffset.dy -
                      (topLeftPosition == null ? 0 : (topLeftPosition.dy+widget.selectRadius/2))
                  : (selectPosition == null ? radius : selectPosition.dy+widget.selectRadius/2),
              //这里减去80，是因为上下边距各40 所以需要减去还有半径
              child: Container(
                width: widget.selectRadius,
                height: widget.selectRadius,
                decoration: BoxDecoration(
                  borderRadius: BorderRadius.circular(widget.selectRadius),
                  border: Border.fromBorderSide(
                      BorderSide(color: widget.selectRingColor)),
                ),
                child: ClipOval(
                  child: Container(
                    color: currentColor,
                  ),
                ),
              ),
            ),
          ],
        ),
      ),
      onTapDown: (e) {
        setState(() {
          isTap = true;
          _initLeftTop();
          if (!isOutSide(e.globalPosition.dx, e.globalPosition.dy)) {
            currentColor =
                getColorAtPoint(e.globalPosition.dx, e.globalPosition.dy);
            currentOffset = e.globalPosition;
            if (widget.selectColorCallBack != null) {
              widget.selectColorCallBack(currentColor);
            }
          }
        });
      },
      onPanUpdate: (e) {
        isTap = true;
        _initLeftTop();
        setState(() {
          if (!isOutSide(e.globalPosition.dx, e.globalPosition.dy)) {
            currentOffset = e.globalPosition;
            currentColor =
                getColorAtPoint(e.globalPosition.dx, e.globalPosition.dy);
            if (widget.selectColorCallBack != null) {
              widget.selectColorCallBack(currentColor);
            }
          }
        });
      },
    );
  }

  void _initLeftTop() {
    if (globalKey.currentContext != null && topLeftPosition == null) {
      final RenderBox box = globalKey.currentContext.findRenderObject();
      topLeftPosition = box.localToGlobal(Offset.zero);
    }
  }

  bool isOutSide(double eventX, double eventY) {
    double x = eventX - (topLeftPosition.dx + radius + widget.padding);
    double y = eventY - (topLeftPosition.dy + radius + widget.padding);
    double r = sqrt(x * x + y * y);
    if (r >= radius) return true;
    return false;
  }

  void _setColor(Color color) {
    //设置颜色值
    var hsvColor = HSVColor.fromColor(color);
    double r = hsvColor.saturation * radius;
    double radian = hsvColor.hue / -180.0 * pi;
    _updateSelector(r * cos(radian), -r * sin(radian));
    currentColor = color;
  }

  void _updateSelector(double eventX, double eventY) {
    //更新选中颜色值
    double r = sqrt(eventX * eventX + eventY * eventY);
    double x = eventX, y = eventY;
    if (r > radius) {
      x *= radius / r;
      y *= radius / r;
    }
    selectPosition =
        new Offset(x + radius + widget.padding, y + radius + widget.padding);
  }

  Color getColorAtPoint(double eventX, double eventY) {
    //获取坐标在色盘中的颜色值
    double x = eventX - (topLeftPosition.dx + radius + widget.padding);
    double y = eventY - (topLeftPosition.dy + radius + widget.padding);
    double r = sqrt(x * x + y * y);
    List<double> hsv = [0.0, 0.0, 1.0];
    hsv[0] = (atan2(-y, -x) / pi * 180).toDouble() + 180;
    hsv[1] = max(0, min(1, (r / radius)));
    return HSVColor.fromAHSV(1.0, hsv[0], hsv[1], hsv[2]).toColor();
  }
}

class ColorPick extends CustomPainter {
  Paint mPaint;
  Paint saturationPaint;
  final List<Color> mCircleColors = new List();
  final List<Color> mStatColors = new List();
  SweepGradient hueShader;
  final radius;
  RadialGradient saturationShader;

  ColorPick({this.radius}) {
    _init();
  }

  void _init() {
    //{Color.RED, Color.YELLOW, Color.GREEN, Color.CYAN, Color.BLUE, Color.MAGENTA, Color.RED}
    mPaint = new Paint();
    saturationPaint = new Paint();
    mCircleColors.add(Color.fromARGB(255, 255, 0, 0));
    mCircleColors.add(Color.fromARGB(255, 255, 255, 0));
    mCircleColors.add(Color.fromARGB(255, 0, 255, 0));
    mCircleColors.add(Color.fromARGB(255, 0, 255, 255));
    mCircleColors.add(Color.fromARGB(255, 0, 0, 255));
    mCircleColors.add(Color.fromARGB(255, 255, 0, 255));
    mCircleColors.add(Color.fromARGB(255, 255, 0, 0));

    mStatColors.add(Color.fromARGB(255, 255, 255, 255));
    mStatColors.add(Color.fromARGB(0, 255, 255, 255));
    hueShader = new SweepGradient(colors: mCircleColors);
    saturationShader = new RadialGradient(colors: mStatColors);
  }

  @override
  void paint(Canvas canvas, Size size) {
    final rect = Rect.fromLTRB(0.0, 0.0, size.width, size.height);
    mPaint.shader = hueShader.createShader(rect);
    saturationPaint.shader = saturationShader.createShader(rect);
    // 注意这一句
    canvas.clipRect(rect);
    canvas.drawCircle(Offset(size.width / 2, size.height / 2), radius, mPaint);
    canvas.drawCircle(
        Offset(size.width / 2, size.height / 2), radius, saturationPaint);
  }

  @override
  bool shouldRepaint(CustomPainter oldDelegate) {
    return false;
  }
}

主页面类：

import 'package:flutter/material.dart';

import 'color_pick.dart';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  final String title;

  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  Color currentColor = Color(0xff0000ff);

  @override
  void initState() {
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: Text(widget.title),
      ),
      body: Column(
        children: <Widget>[
          ColorPickView(
            selectColor: Color(0xff0000ff),
            selectColorCallBack: (color) {
              print(color);
              setState(() {
                currentColor = color;
              });
            },
          ),
          Container(
            color: currentColor,
            height: 100,
            width: 100,
            child: SizedBox(),
          )
        ],
      ),
    );
  }
}

 

其实这里面主要的是绘制和颜色渐变问题，自行绘制这里直接继承CustomPainter，这个继承类里面有两个paint，一个是绘制颜色域的  mPaint，另一个是绘制亮度的saturationPaint，主要用的是SweepGradient扫描/梯度渲染，需要确认圆心坐标。其实就是我们控件宽高的一半。RadialGradient环形渲染。

其实这里绘制比Android简单许多，主要是颜色值获取和选中区域跟随手指移动的问题。

颜色获取：

我们颜色可以分为H、S、V 可以这么解释直接百度如下：

色调H

用角度度量，取值范围为0°～360°，从红色开始按逆时针方向计算，红色为0°，绿色为120°,蓝色为240°。它们的补色是：黄色为60°，青色为180°,品红为300°；

饱和度S

饱和度S表示颜色接近光谱色的程度。一种颜色，可以看成是某种光谱色与白色混合的结果。其中光谱色所占的比例愈大，颜色接近光谱色的程度就愈高，颜色的饱和度也就愈高。饱和度高，颜色则深而艳。光谱色的白光成分为0，饱和度达到最高。通常取值范围为0~1，值越大，颜色越饱和。

亮度V

明度表示颜色明亮的程度，对于光源色，明度值与发光体的光亮度有关；对于物体色，此值和物体的透射比或反射比有关。通常取值范围为0~1。

因此我们可以根据点到圆心距离算出角度代表H  点到圆心的距离与半径比为 S，亮度默认最大不用管。就会有如下算法：

Color getColorAtPoint(double eventX, double eventY) {
    //获取坐标在色盘中的颜色值
    double x = eventX - (topLeftPosition.dx + radius + widget.padding);
    double y = eventY - (topLeftPosition.dy + radius + widget.padding);
    double r = sqrt(x * x + y * y);
    List<double> hsv = [0.0, 0.0, 1.0];
    hsv[0] = (atan2(-y, -x) / pi * 180).toDouble() + 180;
    hsv[1] = max(0, min(1, (r / radius)));
    return HSVColor.fromAHSV(1.0, hsv[0], hsv[1], hsv[2]).toColor();
  }

这个其实就是高中学的数学知识，只不过基本都忘了。这里还支持反选，颜色值确定位置，其实这也就是上面的方法逆向过程，如下：

 void _setColor(Color color) {
    _initLeftTop();
    //设置颜色值
    var hsvColor = HSVColor.fromColor(color);
    double r = hsvColor.saturation * radius;
    double radian = hsvColor.hue / -180.0 * pi;
    _updateSelector(r * cos(radian), -r * sin(radian));
    currentColor = color;
  }

  void _updateSelector(double eventX, double eventY) {
    //更新选中颜色值
    double r = sqrt(eventX * eventX + eventY * eventY);
    double x = eventX, y = eventY;
    if (r > radius) {
      x *= radius / r;
      y *= radius / r;
    }
    currentOffset = new Offset(x + topLeftPosition.dx + radius + widget.padding,
        y + topLeftPosition.dy + radius + widget.padding);
  }

但是这里就需要确定一个问题，就是控件x，y做标，这里用到了这个方法获取x、y做标：

  final RenderBox box = globalKey.currentContext.findRenderObject();
      topLeftPosition = box.localToGlobal(Offset.zero);

不过这个方法有个缺点就是必须渲染完成才能用。

因为选中圈是根据当前控件布局的，而这个触发事件随手指移动的坐标是根据整个屏幕的，因此这个控件的x、y做标需要获取当前控件的x、y坐标，再用触发事件坐标减去当前坐标才能得到选中圈真正的坐标。

github

pub地址