How to draw a custom rounded rectangle border (ShapeBorder), in Flutter?

I'm trying to extend the `ShapeBorder` class to add some functionality. But just playing around with the `paint` method, I found something that I did not expect:

[![enter image description here][1]][1]
The corners of the border and the corners of the rectangle do not seem to match. I used the following code:

class CustomRoundedRectangleBorder extends ShapeBorder {

final double borderWidth;
final BorderRadius borderRadius;

const CustomRoundedRectangleBorder({
this.borderWidth: 1.0,
this.borderRadius: BorderRadius.zero,
})
: assert(borderRadius != null);

@override
EdgeInsetsGeometry get dimensions {
return new EdgeInsets.all(borderWidth);
}

@override
ShapeBorder scale(double t) {
return new CustomRoundedRectangleBorder(
borderWidth: borderWidth * (t),
borderRadius: borderRadius * (t),
);
}

@override
ShapeBorder lerpFrom(ShapeBorder a, double t) {
assert(t != null);
if (a is CustomRoundedRectangleBorder) {
return new CustomRoundedRectangleBorder(
borderWidth: ui.lerpDouble(a.borderWidth, borderWidth, t),
borderRadius: BorderRadius.lerp(a.borderRadius, borderRadius, t),
);
}
return super.lerpFrom(a, t);
}

@override
ShapeBorder lerpTo(ShapeBorder b, double t) {
assert(t != null);
if (b is CustomRoundedRectangleBorder) {
return new CustomRoundedRectangleBorder(
borderWidth: ui.lerpDouble(borderWidth, b.borderWidth, t),
borderRadius: BorderRadius.lerp(borderRadius, b.borderRadius, t),
);
}
return super.lerpTo(b, t);
}

@override
Path getInnerPath(Rect rect, { TextDirection textDirection }) {
return new Path()
..addRRect(borderRadius.resolve(textDirection).toRRect(rect).deflate(
borderWidth));
}

@override
Path getOuterPath(Rect rect, { TextDirection textDirection }) {
return new Path()
..addRRect(borderRadius.resolve(textDirection).toRRect(rect));
}

@override
void paint(Canvas canvas, Rect rect, { TextDirection textDirection }) {
rect = rect.deflate(borderWidth / 2.0);

Paint paint;
final RRect borderRect = borderRadius.resolve(textDirection).toRRect(rect);
paint = new Paint()
..color = Colors.red
..style = PaintingStyle.stroke
..strokeWidth = borderWidth;
canvas.drawRRect(borderRect, paint);
}
}
And created the rectangle as follows:

new Container(
height: 100.0,
width: 200.0,
padding: new EdgeInsets.all(10.0),
decoration: new ShapeDecoration(
color: Colors.black,
shape: new CustomRoundedRectangleBorder(
borderRadius: new BorderRadius.all(new Radius.circular(20.0)),
borderWidth: 10.0,
),
// side: new BorderSide(color: Colors.white)
),
child: new Center(child: new Text("My Button"),),
),
I feel like the Flutter source code takes a similar approach, but perhaps I'm not seeing something.

**EDIT**
Changing the `style` of my `paint` to `PaintingStyle.fill` thus drawing a rectangle over the original rectangle instead of borders, I do seem to get the correct borders:

void paint(Canvas canvas, Rect rect, { TextDirection textDirection }) {

// rect = rect.deflate(borderWidth / 2.0);

Paint paint;
final RRect borderRect = borderRadius.resolve(textDirection).toRRect(rect);
paint = new Paint()
..color = Colors.red.withOpacity(0.25)
..style = PaintingStyle.fill
..strokeWidth = borderWidth;
canvas.drawRRect(borderRect, paint);
}
I'm still puzzled on how to do this...
[1]:

You should use canvas.drawPath not drawRect

Paint paint = new Paint()
..color = borderColor
..style = PaintingStyle.stroke
..strokeWidth = borderWidth;

canvas.drawPath(getOuterPath(rect), paint);

also if you just want a border, its enough to use

@override
Path getInnerPath(Rect rect, {TextDirection textDirection}) {
return new Path()
..fillType = PathFillType.evenOdd
..addPath(getOuterPath(rect), Offset.zero);
}

You can use `canvas.drawRRect` :

canvas.drawRRect(RRect.fromRectAndRadius(Rect.fromLTWH(size.width / 2 - gap - smallMarkWidth - 15,gap * 8,gap + 70,gap * 5,),Radius.circular(15.0)),backgroundPaint);

Draw custom rounded border with shadow.

new Container(

decoration:
new BoxDecoration(
borderRadius: new BorderRadius.circular(10.0),
color: Colors.white,

boxShadow: [
new BoxShadow(
color: Colors.grey,
blurRadius: 3.0,
offset: new Offset(1.0, 1.0))
],
),
)

Draw custom rounded border without shadow.

new Container(
decoration:
new BoxDecoration(
borderRadius: new BorderRadius.circular(10.0),
color: Colors.grey,


),
)

You can use [ClipRRect][1] widget instead of drawRect and it is simple to use.

ClipRRect(
borderRadius: BorderRadius.circular(10),
child: Container(),
),


[1]:

[To see links please register here]

I published a simple package based off @Bram Vanbilsen's code, which gives you control on how you want to draw the shape and it's border whichever way you want.

The package can be found on pub.dev here:

[To see links please register here]

This worked for me!


class MyButton extends StatelessWidget {
@override
Widget build(BuildContext context) {
return DecoratedBox(
decoration:
ShapeDecoration(
shape: RoundedRectangleBorder(
side:new BorderSide(color: Color(0xFF2A8068)),
borderRadius: new BorderRadius.all(new Radius.circular(4))),
color: Color(0xFF2A8068)),
child: Theme(
data: Theme.of(context).copyWith(
buttonTheme: ButtonTheme.of(context).copyWith(
materialTapTargetSize: MaterialTapTargetSize.shrinkWrap)),
child: OutlineButton(
shape: RoundedRectangleBorder(
side:new BorderSide(color: Color(0xFF2A8068)), //the outline color
borderRadius: new BorderRadius.all(new Radius.circular(4))),
child: Text(
"ابدأ", //your text here
style: new TextStyle(
color: Colors.white, //your textColor
),
),
onPressed: () => {},
),
),
);