Flutter 将阴影应用于 CustomPainted 小部件

Question

介绍

我使用 Flutter 的 CustomPaint Widget 绘制了一个自定义标签栏，它看起来像这样:

此外，这是我用来绘制小部件的代码:

class TabBarPainter extends CustomPainter {
  final Color paintColor = Colors.redAccent 
  @override
  void paint(Canvas canvas, Size size) {
    /// the thing that I called as a deleter circle is an imaginary circle that I used to delete a semicircle from my rectangular shape

    var diameter = 80; /// X value is the diameter(R) of the deleter circle;
    double topSpace = 2;
    double startCurve = (size.width-diameter)/2; /// Start point of the curve
    double endCurve = startCurve+diameter; // End Point of the curve


     /// Some math about my cubic bezier curve
    double xValueInset = diameter * 0.05; 
    double yValueOffset = (diameter/2) * 4.0 / 3.0; 

    Path path = Path();

    Paint paint = Paint();

    /// Points to make a semicircle approximation using Bezier Curve
    var firstendPoint = new Offset(endCurve, topSpace);
    var controlPoint1  = new Offset(startCurve+xValueInset,yValueOffset+topSpace);
    var controlPoint2  = new Offset((diameter-xValueInset)+startCurve,yValueOffset+topSpace);

    //! Start sketching Shape
    path.moveTo(0.0,topSpace);
    path.lineTo(startCurve, topSpace);
    path.cubicTo(controlPoint1.dx, controlPoint1.dy,
    controlPoint2.dx, controlPoint2.dy,
    firstendPoint.dx, firstendPoint.dy);
    path.lineTo(size.width, topSpace);
    path.lineTo(size.width, size.height);
    path.lineTo(0.0, size.height);
    path.close();
    //! End sketching Shape

    paint.color = paintColor;

    canvas.drawPath(path, paint);

  }

  @override
  bool shouldRepaint(TabBarPainter oldDelegate) =>  oldDelegate != this;
}

实验

我想在我的 CustomDrawen Shape 上应用一个 shodow，所以我尝试了 2 种方法:

第一种方法:我使用了经典的容器和 boxshadow 对其进行阴影处理，它看起来像这样: 我使用了以下代码:

Container(
  decoration: BoxDecoration(
    boxShadow: [
      BoxShadow(
        color : Colors.black.withOpacity(0.30),
        blurRadius: 3,
        ffset: new Offset(0, -3)
      )
    ]
  ),
  child: CustomPaint(           
    painter: TabBarPainter(),
  ),

第二种方法:我画了一个类似的黑色(不透明度(0.15))形状 它看起来像这样:

我将以下代码添加到我的 CustomPainter 中以绘制此形状:

final Color shadowColor = Colors.black.withOpacity(0.15);

Path shadowPath = Path();
Paint shadowPaint = Paint();

/// Points to make a semicircle approximation using Bezier Curve

var shadowfirstendPoint = new Offset(endCurve-topSpace, 0.0);
var shadowcontrolPoint1  = new Offset(startCurve+xValueInset+topSpace,yValueOffset);
var shadowcontrolPoint2  = new Offset((diameter-xValueInset)+startCurve-topSpace,yValueOffset);

//! Start sketching Shadow   
shadowPath.lineTo(startCurve+topSpace, 0.0);
shadowPath.cubicTo(shadowcontrolPoint1.dx, shadowcontrolPoint1.dy,
shadowcontrolPoint2.dx, shadowcontrolPoint2.dy,
shadowfirstendPoint.dx, shadowfirstendPoint.dy);
shadowPath.lineTo(size.width, 0.0);
shadowPath.lineTo(size.width, size.height);
shadowPath.lineTo(0.0, size.height);
shadowPath.close();

//! End Sketching Shadow
shadowPaint.color = shadowColor;
canvas.drawPath(shadowPath, shadowPaint);

问题

在第一种方法中，空白区域 - 在小部件的顶部中心 - 被阴影填充

在第二种方法中，阴影不真实，因为即使它具有低不透明度，它也没有模糊，我找不到使它模糊的方法

结论

我需要另一种方法来正确地为我的小部件添加阴影或为我的类似阴影的自定义绘制形状添加模糊

由于 flutter 对他们创建的每种类型的小部件都这样做，所以这似乎是可能的

我会感谢任何帮助

问候

Answer 1

我发现一个更简单的方法是偏移路径

canvas.drawShadow(path.shift(Offset(0, -5)), Colors.black, 2.0, true);