我已经尝试使用Canvas.clipPath和GestureDetector，使其像画布上的橡皮擦一样。在Container内使用CustomPaint与设置了imageDecoration的Canvas.drawPath或许可以找到另一个解决方法。
final Paint _eraserPaint = Paint()
..color = Colors.transparent
..blendMode = BlendMode.clear
..strokeWidth = 8
..style = PaintingStyle.stroke
..isAntiAlias = true;
但它会画出黑线而不是擦除。
有什么办法可以解决这个问题吗？
谢谢。
saveLayer。完成这个步骤后（为您创建一个新图层供您使用），您可以使用任何Color填充或使用BlendMode.clear擦除进行绘制。最后，调用restore将新图层“合并”到其他现有图层中。void paint(Canvas canvas, Size size) {
canvas.saveLayer(Rect.largest, Paint());
canvas.drawRect(Rect.fromLTWH(0, 0, 80, 80), Paint()..color = Colors.red);
canvas.drawCircle(Offset(40, 40), 40, Paint()..blendMode = BlendMode.clear);
canvas.restore();
}
示例结果：
希望这段代码能对你有所帮助！
class DrawingPainter extends CustomPainter {
List<DrawingPoints> pointsList;
List<Offset> offsetPoints = List();
DrawingPainter({
this.pointsList,
});
@override
void paint(Canvas canvas, Size size) {
canvas.saveLayer(Rect.fromLTWH(0, 0, size.width, size.height), Paint());
for (int i = 0; i < pointsList.length - 1; i++) {
if (pointsList[i] != null && pointsList[i + 1] != null) {
canvas.drawLine(pointsList[i].points, pointsList[i + 1].points, pointsList[i].paint);
canvas.drawCircle(pointsList[i].points, pointsList[i].paint.strokeWidth/2, pointsList[i].paint);
}
}
canvas.restore();
}
@override
bool shouldRepaint(DrawingPainter oldDelegate) => true;
}
class DrawingPoints {
Paint paint;
Offset points;
DrawingPoints({this.points, this.paint});
}
您需要使用saveLayer函数，然后将其还原来保存Paint。
可能您需要将此代码添加到Stateful小部件中。
void changeBrush(bool isErease){
setState(() {
if ( isErease ){
paint = Paint();
paint.blendMode = BlendMode.clear;
paint.color = Colors.white;
paint.strokeWidth = strokeWidth;
}else{
paint = Paint();
paint.isAntiAlias = true;
paint.color = selectedColor.withOpacity(opacity);
paint.strokeWidth = strokeWidth;
}
});
}
来到这里是为了寻找相反的效果（剪裁正方形的角落并保留内部）。目标是从几个非圆角重叠的矩形中绘制出一个圆角矩形。
以下是实现该效果的方法：
canvas.save();
RRect clipRectangle = RRect.fromRectAndRadius(
Rect.fromLTWH(0, 0, 80, 80),
Radius.circular(4),
);
canvas.clipRRect(clipRectangle);
canvas.drawRect(Rect.fromLTWH(0, 0, 80, 80), Paint()..color = Colors.red);
canvas.drawRect(Rect.fromLTWH(0, 20, 80, 80), Paint()..color = Colors.blue);
canvas.restore();
Opacity(
opacity: .99,
child: CustomPaint(
size: const Size(double.infinity, 100),
painter: MyPainter(),
),
),
希望这段代码能对你有所帮助...
import 'dart:convert';
import 'dart:io';
import 'dart:typed_data';
import 'dart:ui' as ui;
import 'package:animated_floatactionbuttons/animated_floatactionbuttons.dart';
import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart';
import 'package:flutter/services.dart';
import 'package:image_gallery_saver/image_gallery_saver.dart';
import 'package:image_picker/image_picker.dart';
import 'package:permission_handler/permission_handler.dart';
var appbarcolor = Colors.blue;
class CanvasPainting_test extends StatefulWidget {
@override
_CanvasPainting_testState createState() => _CanvasPainting_testState();
}
class _CanvasPainting_testState extends State<CanvasPainting_test> {
GlobalKey globalKey = GlobalKey();
List<TouchPoints> points = List();
double opacity = 1.0;
StrokeCap strokeType = StrokeCap.round;
double strokeWidth = 3.0;
double strokeWidthforEraser = 3.0;
Color selectedColor;
Future<void> _pickStroke() async {
//Shows AlertDialog
return showDialog<void>(
context: context,
//Dismiss alert dialog when set true
barrierDismissible: true, // user must tap button!
builder: (BuildContext context) {
//Clips its child in a oval shape
return ClipOval(
child: AlertDialog(
//Creates three buttons to pick stroke value.
actions: <Widget>[
//Resetting to default stroke value
FlatButton(
child: Icon(
Icons.clear,
),
onPressed: () {
strokeWidth = 3.0;
Navigator.of(context).pop();
},
),
FlatButton(
child: Icon(
Icons.brush,
size: 24,
),
onPressed: () {
strokeWidth = 10.0;
Navigator.of(context).pop();
},
),
FlatButton(
child: Icon(
Icons.brush,
size: 40,
),
onPressed: () {
strokeWidth = 30.0;
Navigator.of(context).pop();
},
),
FlatButton(
child: Icon(
Icons.brush,
size: 60,
),
onPressed: () {
strokeWidth = 50.0;
Navigator.of(context).pop();
},
),
],
),
);
},
);
}
Future<void> _opacity() async {
//Shows AlertDialog
return showDialog<void>(
context: context,
//Dismiss alert dialog when set true
barrierDismissible: true,
builder: (BuildContext context) {
//Clips its child in a oval shape
return ClipOval(
child: AlertDialog(
//Creates three buttons to pick opacity value.
actions: <Widget>[
FlatButton(
child: Icon(
Icons.opacity,
size: 24,
),
onPressed: () {
//most transparent
opacity = 0.1;
Navigator.of(context).pop();
},
),
FlatButton(
child: Icon(
Icons.opacity,
size: 40,
),
onPressed: () {
opacity = 0.5;
Navigator.of(context).pop();
},
),
FlatButton(
child: Icon(
Icons.opacity,
size: 60,
),
onPressed: () {
//not transparent at all.
opacity = 1.0;
Navigator.of(context).pop();
},
),
],
),
);
},
);
}
Future<void> _pickStrokeforEraser() async {
//Shows AlertDialog
return showDialog<void>(
context: context,
//Dismiss alert dialog when set true
barrierDismissible: true, // user must tap button!
builder: (BuildContext context) {
//Clips its child in a oval shape
return ClipOval(
child: AlertDialog(
//Creates three buttons to pick stroke value.
actions: <Widget>[
//Resetting to default stroke value
FlatButton(
child: Icon(
Icons.clear,
),
onPressed: () {
strokeWidthforEraser = 3.0;
Navigator.of(context).pop();
},
),
FlatButton(
child: Icon(
Icons.brush,
size: 24,
),
onPressed: () {
strokeWidthforEraser = 10.0;
Navigator.of(context).pop();
},
),
FlatButton(
child: Icon(
Icons.brush,
size: 40,
),
onPressed: () {
strokeWidthforEraser = 30.0;
Navigator.of(context).pop();
},
),
FlatButton(
child: Icon(
Icons.brush,
size: 60,
),
onPressed: () {
strokeWidthforEraser = 50.0;
Navigator.of(context).pop();
},
),
],
),
);
},
);
}
Future<void> _save() async {
RenderRepaintBoundary boundary =
globalKey.currentContext.findRenderObject();
ui.Image image = await boundary.toImage();
ByteData byteData = await image.toByteData(format: ui.ImageByteFormat.png);
Uint8List pngBytes = byteData.buffer.asUint8List();
//Request permissions if not already granted
if (!(await Permission.storage.status.isGranted))
await Permission.storage.request();
final result = await ImageGallerySaver.saveImage(
Uint8List.fromList(pngBytes),
quality: 60,
name: "canvas_image");
print(result);
}
String erase = 'yes';
List<Widget> fabOption() {
return <Widget>[
FloatingActionButton(
backgroundColor: appbarcolor,
heroTag: "camera",
child: Icon(Icons.camera),
tooltip: 'camera',
onPressed: () {
//min: 0, max: 50
setState(() {
erase = 'yes';
this._showDialog();
// _save();
});
},
),
FloatingActionButton(
backgroundColor: appbarcolor,
heroTag: "paint_save",
child: Icon(Icons.file_download),
tooltip: 'Save',
onPressed: () {
//min: 0, max: 50
setState(() {
erase = 'yes';
_save();
});
},
),
FloatingActionButton(
backgroundColor: appbarcolor,
heroTag: "paint_stroke",
child: Icon(Icons.brush),
tooltip: 'Stroke',
onPressed: () {
//min: 0, max: 50
setState(() {
erase = 'yes';
_pickStroke();
});
},
),
// FloatingActionButton(
// heroTag: "paint_opacity",
// child: Icon(Icons.opacity),
// tooltip: 'Opacity',
// onPressed: () {
// //min:0, max:1
// setState(() {
// _opacity();
// });
// },
// ),
FloatingActionButton(
backgroundColor: appbarcolor,
heroTag: "Erase",
child: Icon(Icons.ac_unit),
tooltip: 'Erase',
onPressed: () {
//min: 0, max: 50
setState(() {
// _save();
// selectedColor = Colors.transparent;
// print(Platform.isAndroid);
erase = 'no';
_pickStrokeforEraser();
});
},
),
FloatingActionButton(
backgroundColor: appbarcolor,
heroTag: "Clear All",
child: Icon(Icons.clear),
tooltip: "Clear All",
onPressed: () {
setState(() {
erase = 'yes';
points.clear();
});
}),
FloatingActionButton(
backgroundColor: Colors.white,
heroTag: "color_red",
child: colorMenuItem(Colors.red),
tooltip: 'Color',
onPressed: () {
setState(() {
selectedColor = Colors.red;
});
},
),
FloatingActionButton(
backgroundColor: Colors.white,
heroTag: "color_green",
child: colorMenuItem(Colors.green),
tooltip: 'Color',
onPressed: () {
setState(() {
erase = 'yes';
selectedColor = Colors.green;
});
},
),
FloatingActionButton(
backgroundColor: Colors.white,
heroTag: "color_pink",
child: colorMenuItem(Colors.pink),
tooltip: 'Color',
onPressed: () {
setState(() {
selectedColor = Colors.pink;
});
},
),
FloatingActionButton(
backgroundColor: Colors.white,
heroTag: "color_blue",
child: colorMenuItem(Colors.blue),
tooltip: 'Color',
onPressed: () {
setState(() {
erase = 'yes';
selectedColor = Colors.blue;
});
},
),
];
}
void _showDialog() {
// flutter defined function
showDialog(
context: context,
builder: (BuildContext context) {
// return object of type Dialog
return AlertDialog(
// title: new Text("Alert Dialog title"),
content: Row(
// mainAxisSize: MainAxisSize.min,
children: <Widget>[
RaisedButton(
onPressed: getImageCamera,
child: Text('From Camera'),
),
SizedBox(
width: 5,
),
RaisedButton(
onPressed: getImageGallery,
child: Text('From Gallery'),
)
],
),
);
},
);
}
File _image;
Future getImageCamera() async {
var image = await ImagePicker.pickImage(source: ImageSource.camera);
print(image);
if (image != null) {
setState(() {
_image = image;
});
Navigator.of(context, rootNavigator: true).pop('dialog');
}
}
Future getImageGallery() async {
var image = await ImagePicker.pickImage(source: ImageSource.gallery);
print(image);
if (image != null) {
setState(() {
_image = image;
print(_image);
});
Navigator.of(context, rootNavigator: true).pop('dialog');
}
}
/*-------------------------------------*/
@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text('paint on image and erase'),backgroundColor: Colors.blueGrey
// leading: IconButton(
// icon: Icon(Icons.arrow_back_ios),onPressed: (){
// Navigator.pop(context);
// },),
),
body: GestureDetector(
onPanUpdate: (details) {
setState(() {
RenderBox renderBox = context.findRenderObject();
erase!='no'? points.add(TouchPoints(
points: renderBox.globalToLocal(details.globalPosition),
paint: Paint()
..strokeCap = strokeType
..isAntiAlias = true
..color = selectedColor.withOpacity(opacity)
..strokeWidth = strokeWidth))
: points.add(TouchPoints(
points: renderBox.globalToLocal(details.globalPosition),
paint: Paint()
..color = Colors.transparent
..blendMode = BlendMode.clear
..strokeWidth = strokeWidthforEraser
..style = PaintingStyle.stroke
..isAntiAlias = true
));
});
},
onPanStart: (details) {
setState(() {
RenderBox renderBox = context.findRenderObject();
erase!='no'? points.add(TouchPoints(
points: renderBox.globalToLocal(details.globalPosition),
paint: Paint()
..strokeCap = strokeType
..isAntiAlias = true
..color = selectedColor.withOpacity(opacity)
..strokeWidth = strokeWidth))
: points.add(TouchPoints(
points: renderBox.globalToLocal(details.globalPosition),
paint: Paint()
..color = Colors.transparent
..blendMode = BlendMode.clear
..strokeWidth = strokeWidthforEraser
..style = PaintingStyle.stroke
..isAntiAlias = true
));
});
},
onPanEnd: (details) {
setState(() {
points.add(null);
});
},
child: RepaintBoundary(
key: globalKey,
child: Stack(
children: <Widget>[
Center(
child: _image == null
? Image.asset(
"assets/images/helo.jfif",
)
: Image.file(_image),
),
CustomPaint(
size: Size.infinite,
painter: MyPainter(
pointsList: points,
),
),
],
),
),
),
floatingActionButton: AnimatedFloatingActionButton(
fabButtons: fabOption(),
colorStartAnimation: appbarcolor,
colorEndAnimation: Colors.red[300],
animatedIconData: AnimatedIcons.menu_close),
);
}
Widget colorMenuItem(Color color) {
return GestureDetector(
onTap: () {
setState(() {
selectedColor = color;
});
},
child: ClipOval(
child: Container(
padding: const EdgeInsets.only(bottom: 8.0),
height: 36,
width: 36,
color: color,
),
),
);
}
}
class MyPainter extends CustomPainter {
MyPainter({this.pointsList});
//Keep track of the points tapped on the screen
List<TouchPoints> pointsList;
List<Offset> offsetPoints = List();
//This is where we can draw on canvas.
@override
void paint(Canvas canvas, Size size) {
canvas.saveLayer(Rect.fromLTWH(0, 0, size.width, size.height), Paint());
for (int i = 0; i < pointsList.length - 1; i++) {
if (pointsList[i] != null && pointsList[i + 1] != null) {
canvas.drawLine(pointsList[i].points, pointsList[i + 1].points, pointsList[i].paint);
canvas.drawCircle(pointsList[i].points, pointsList[i].paint.strokeWidth/2, pointsList[i].paint);
}
}
canvas.restore();
}
//Called when CustomPainter is rebuilt.
//Returning true because we want canvas to be rebuilt to reflect new changes.
@override
bool shouldRepaint(MyPainter oldDelegate) => true;
}
//Class to define a point touched at canvas
class TouchPoints {
Paint paint;
Offset points;
TouchPoints({this.points, this.paint});
}