drawArc（绘制弧线）
drawArc(Rect rect, double startAngle, double sweepAngle, bool useCenter, Paint paint)| rect | 构造矩形 |
| startAngle | 开始角度 |
| sweepAngle | 绘制的弧形占用角度弧度(360°角=2π) |
| userCenter | 扇形或圆弧段（true或false） |
| paint | 画笔 |
/// The PI constant.
const double pi = 3.1415926535897932;paint（画笔）
| isAntiAlias | 是否抗锯齿（bool） |
| strokeWidth | 画笔宽度 （double） |
| color | 画笔颜色（Color） |
| strokeCap | 延伸绘制（画 冒） |
| invertColors | 转换颜色值（二进制补码） |
useCenter=false（绘制圆弧段）
Rect.fromCircle({ Offset center, double radius })| center | 圆弧中心点（相对于原点的偏移量） |
| radius | 圆弧半径(double) |
class MyPainter extends CustomPainter {
@override
void paint(Canvas canvas, Size size) {
var paint = Paint()
..isAntiAlias = true
..strokeWidth=0.0
..color=Colors.redAccent
..invertColors=false;
Rect rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 100.0);
canvas.drawArc(rect, 0.0, 2*pi/4, false, paint);
}
//在实际场景中正确利用此回调可以避免重绘开销，本示例我们简单的返回true
@override
bool shouldRepaint(CustomPainter oldDelegate) => true;
}Rect.fromLTRB(this.left, this.top, this.right, this.bottom)| left | 矩形最左边相对于原点(0,0)偏移量 |
| top | 矩形最顶部相对于原点(0,0)偏移量 |
| right | 矩形最右边相对于原点(0,0)偏移量 |
| bottom | 矩形最底部相对于原点(0,0)偏移量 |
class MyPainter extends CustomPainter {
@override
void paint(Canvas canvas, Size size) {
var paint = Paint()
..isAntiAlias = true
..strokeWidth=0.0
..color=Colors.redAccent
..invertColors=false;
Rect rect=Rect.fromLTRB(0.0, 0.0, size.width, size.height/2);
canvas.drawArc(rect, 0.0, 2*pi/4, false, paint);
}
//在实际场景中正确利用此回调可以避免重绘开销，本示例我们简单的返回true
@override
bool shouldRepaint(CustomPainter oldDelegate) => true;
}
Rect.fromCenter({ Offset center, double width, double height })| center | 矩形中心相对于原点偏移量 |
| width | 矩形宽度 |
| height | 矩形高度 |
class MyPainter extends CustomPainter {
@override
void paint(Canvas canvas, Size size) {
var paint = Paint()
..isAntiAlias = true
..strokeWidth=0.0
..color=Colors.redAccent
..invertColors=false;
Rect rect=Rect.fromCenter(center: Offset(size.width/2,size.height/2),width:size.width/2,height:size.height/2);
canvas.drawArc(rect, 0.0, 2*pi/4, false, paint);
}
//在实际场景中正确利用此回调可以避免重绘开销，本示例我们简单的返回true
@override
bool shouldRepaint(CustomPainter oldDelegate) => true;
}
Rect.fromLTWH(double left, double top, double width, double height)| left | 矩形最左边相对于原点偏移量 |
| top | 矩形最顶部相对于原点偏移量 |
| width | 矩形宽度 |
| height | 矩形高度 |
class MyPainter extends CustomPainter {
@override
void paint(Canvas canvas, Size size) {
var paint = Paint()
..isAntiAlias = true
..strokeWidth=0.0
..color=Colors.redAccent
..invertColors=false;
Rect rect=Rect.fromLTWH(0.0, 0.0, size.width/2, size.height/2);
canvas.drawArc(rect, 0.0, 2*pi/4, false, paint);
}
//在实际场景中正确利用此回调可以避免重绘开销，本示例我们简单的返回true
@override
bool shouldRepaint(CustomPainter oldDelegate) => true;
}
Rect.fromPoints(Offset a, Offset b) : this.fromLTRB(
math.min(a.dx, b.dx),
math.min(a.dy, b.dy),
math.max(a.dx, b.dx),
math.max(a.dy, b.dy),
);| a | 相对于原点x方向上的偏移范围 |
| b | 相对于原点y方向上的偏移范围 |
下面三种写法效果一样（主要是取x或y方向上偏移量的范围）
class MyPainter extends CustomPainter {
@override
void paint(Canvas canvas, Size size) {
var paint = Paint()
..isAntiAlias = true
..strokeWidth=1.0
..color=Colors.redAccent
..invertColors=false;
Rect rect=Rect.fromPoints(Offset(size.width, 0.0),Offset(0,size.height));
canvas.drawArc(rect, 0.0, 2*pi/4, false, paint);
}
//在实际场景中正确利用此回调可以避免重绘开销，本示例我们简单的返回true
@override
bool shouldRepaint(CustomPainter oldDelegate) => true;
}class MyPainter extends CustomPainter {
@override
void paint(Canvas canvas, Size size) {
var paint = Paint()
..isAntiAlias = true
..strokeWidth=1.0
..color=Colors.redAccent
..invertColors=false;
Rect rect=Rect.fromPoints(Offset(0.0, 0.0),Offset(size.width,size.height));
canvas.drawArc(rect, 0.0, 2*pi/4, false, paint);
}
//在实际场景中正确利用此回调可以避免重绘开销，本示例我们简单的返回true
@override
bool shouldRepaint(CustomPainter oldDelegate) => true;
}class MyPainter extends CustomPainter {
@override
void paint(Canvas canvas, Size size) {
var paint = Paint()
..isAntiAlias = true
..strokeWidth=1.0
..color=Colors.redAccent
..invertColors=false;
Rect rect=Rect.fromPoints(Offset(size.width, size.height),Offset(0.0,0.0));
canvas.drawArc(rect, 0.0, 2*pi/4, false, paint);
}
//在实际场景中正确利用此回调可以避免重绘开销，本示例我们简单的返回true
@override
bool shouldRepaint(CustomPainter oldDelegate) => true;
}useCenter=false（绘制扇形）
class MyPainter extends CustomPainter {
@override
void paint(Canvas canvas, Size size) {
var paint = Paint()
..isAntiAlias = true
..strokeWidth=0.0
..color=Colors.redAccent
..invertColors=false;
Rect rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 100.0);
canvas.drawArc(rect, 0.0, 2*pi/4, true, paint);
}
//在实际场景中正确利用此回调可以避免重绘开销，本示例我们简单的返回true
@override
bool shouldRepaint(CustomPainter oldDelegate) => true;
}
class MyPainter extends CustomPainter {
@override
void paint(Canvas canvas, Size size) {
var paint = Paint()
..isAntiAlias = true
..strokeWidth=0.0
..color=Colors.redAccent
..invertColors=false;
Rect rect=Rect.fromLTRB(0.0, 0.0, size.width, size.height/2);
canvas.drawArc(rect, 0.0, 2*pi/4, true, paint);
}
//在实际场景中正确利用此回调可以避免重绘开销，本示例我们简单的返回true
@override
bool shouldRepaint(CustomPainter oldDelegate) => true;
}Rect.lerp(在两个矩形之间进行线性插值)
源码：
static Rect lerp(Rect a, Rect b, double t) {
assert(t != null);
if (a == null && b == null)
return null;
if (a == null)
return Rect.fromLTRB(b.left * t, b.top * t, b.right * t, b.bottom * t);
if (b == null) {
final double k = 1.0 - t;
return Rect.fromLTRB(a.left * k, a.top * k, a.right * k, a.bottom * k);
}
return Rect.fromLTRB(
lerpDouble(a.left, b.left, t),
lerpDouble(a.top, b.top, t),
lerpDouble(a.right, b.right, t),
lerpDouble(a.bottom, b.bottom, t),
);
}double lerpDouble(num a, num b, double t) {
if (a == null && b == null)
return null;
a ??= 0.0;
b ??= 0.0;
return a + (b - a) * t;
}| a | 矩形 |
| b | 矩形 |
| t | 时间值（0.0~1.0之间） |
class MyPainter extends CustomPainter {
@override
void paint(Canvas canvas, Size size) {
var paint = Paint()
..isAntiAlias = true
..strokeWidth=0.0
..color=Colors.redAccent
..invertColors=false;
Rect a=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: size.width/3);
Rect b=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: size.width/2);
Rect rect=Rect.lerp(a, b, 1.0);
canvas.drawArc(rect, 0.0, 2*pi/4, true, paint);
rect=Rect.lerp(a, b, 0.2);
canvas.drawArc(rect, 0.0, 2*pi/4, true, paint..color=Colors.blue);
}
//在实际场景中正确利用此回调可以避免重绘开销，本示例我们简单的返回true
@override
bool shouldRepaint(CustomPainter oldDelegate) => true;
}
class MyPainter extends CustomPainter {
@override
void paint(Canvas canvas, Size size) {
var paint = Paint()
..isAntiAlias = true
..strokeWidth=0.0
..color=Colors.redAccent
..invertColors=false;
Rect a=Rect.fromLTRB(80.0, 80.0, size.width-30.0, size.height-60.0);
Rect b=Rect.fromLTRB(50.0, 50.0, size.width-20.0, size.height-20.0);
Rect rect=Rect.lerp(a, b, 1.0);
canvas.drawArc(rect, 0.0, 2*pi/4, true, paint);
rect=Rect.lerp(a, b, 0.2);
canvas.drawArc(rect, 0.0, 2*pi/4, true, paint..color=Colors.blue);
}
//在实际场景中正确利用此回调可以避免重绘开销，本示例我们简单的返回true
@override
bool shouldRepaint(CustomPainter oldDelegate) => true;
}
class MyPainter extends CustomPainter {
@override
void paint(Canvas canvas, Size size) {
var paint = Paint()
..isAntiAlias = true
..strokeWidth=0.0
..color=Colors.redAccent
..invertColors=false;
Rect a=Rect.fromLTRB(80.0, 80.0, size.width-80.0, size.height-80.0);
Rect b=Rect.fromLTRB(50.0, 50.0, size.width-50.0, size.height-50.0);
Rect rect=Rect.lerp(a, b, 1.0);
canvas.drawArc(rect, 0.0, 2*pi/4, true, paint);
rect=Rect.lerp(a, b, 0.7);
canvas.drawArc(rect, 0.0, 2*pi/4, true, paint..color=Colors.blue);
rect=Rect.lerp(a, b, 0.5);
canvas.drawArc(rect, 0.0, 2*pi/4, true, paint..color=Colors.green);
rect=Rect.lerp(a, b, 0.3);
canvas.drawArc(rect, 0.0, 2*pi/4, true, paint..color=Colors.deepPurpleAccent);
rect=Rect.lerp(a, b, 0.1);
canvas.drawArc(rect, 0.0, 2*pi/4, true, paint..color=Colors.cyanAccent);
rect=Rect.lerp(a, b, -0.2);
canvas.drawArc(rect, 0.0, 2*pi/4, true, paint..color=Colors.lightGreenAccent);
}
//在实际场景中正确利用此回调可以避免重绘开销，本示例我们简单的返回true
@override
bool shouldRepaint(CustomPainter oldDelegate) => true;
}画圆
class MyPainter extends CustomPainter {
@override
void paint(Canvas canvas, Size size) {
var paint = Paint()
..isAntiAlias = true
..strokeWidth=0.0
..color=Colors.redAccent
..invertColors=false;
Rect rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 100.0);
canvas.drawArc(rect, 0.0, 2*pi, false, paint);
}
//在实际场景中正确利用此回调可以避免重绘开销，本示例我们简单的返回true
@override
bool shouldRepaint(CustomPainter oldDelegate) => true;
}画同心圆
class MyPainter extends CustomPainter {
@override
void paint(Canvas canvas, Size size) {
var paint = Paint()
..isAntiAlias = true
..strokeWidth=0.0
..color=Colors.redAccent
..invertColors=false;
Rect rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 100.0);
canvas.drawArc(rect, 0.0, 2*pi, false, paint);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 80.0);
canvas.drawArc(rect, 0.0, 2*pi, false, paint..color=Colors.blue);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 60.0);
canvas.drawArc(rect, 0.0, 2*pi, false, paint..color=Colors.deepPurple);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 40.0);
canvas.drawArc(rect, 0.0, 2*pi, false, paint..color=Colors.lightGreenAccent);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 20.0);
canvas.drawArc(rect, 0.0, 2*pi, false, paint..color=Colors.grey);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 10.0);
canvas.drawArc(rect, 0.0, 2*pi, false, paint..color=Colors.pinkAccent);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 2.0);
canvas.drawArc(rect, 0.0, 2*pi, false, paint..color=Colors.blueAccent);
}
//在实际场景中正确利用此回调可以避免重绘开销，本示例我们简单的返回true
@override
bool shouldRepaint(CustomPainter oldDelegate) => true;
}绘制渐变圆
class MyPainter extends CustomPainter {
@override
void paint(Canvas canvas, Size size) {
var paint = Paint()
..isAntiAlias = true
..strokeWidth=0.0
..invertColors=false;
Rect rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 100.0);
canvas.drawArc(rect, 0.0, 2*pi, false, paint..color=Colors.redAccent.withOpacity(0.2));
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 80.0);
canvas.drawArc(rect, 0.0, 2*pi, false, paint..color=Colors.redAccent.withOpacity(0.3));
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 60.0);
canvas.drawArc(rect, 0.0, 2*pi, false, paint..color=Colors.redAccent.withOpacity(0.4));
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 40.0);
canvas.drawArc(rect, 0.0, 2*pi, false, paint..color=Colors.redAccent.withOpacity(0.5));
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 20.0);
canvas.drawArc(rect, 0.0, 2*pi, false, paint..color=Colors.redAccent.withOpacity(0.6));
}
//在实际场景中正确利用此回调可以避免重绘开销，本示例我们简单的返回true
@override
bool shouldRepaint(CustomPainter oldDelegate) => true;
}同心圆段拼凑正矩形
class MyPainter extends CustomPainter {
@override
void paint(Canvas canvas, Size size) {
var paint = Paint()
..isAntiAlias = true
..strokeWidth=0.0
..invertColors=false;
Rect rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 100.0);
canvas.drawArc(rect, 0, 2*pi/4, false, paint..color=Colors.redAccent);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 100.0);
canvas.drawArc(rect, 2*pi/4, 2*pi/4, false, paint..color=Colors.redAccent);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 100.0);
canvas.drawArc(rect, 2*pi/2, 2*pi/4, false, paint..color=Colors.redAccent);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 100.0);
canvas.drawArc(rect, 2*pi/4*3, 2*pi/4, false, paint..color=Colors.redAccent);
}
//在实际场景中正确利用此回调可以避免重绘开销，本示例我们简单的返回true
@override
bool shouldRepaint(CustomPainter oldDelegate) => true;
}画不同颜色等分弧度
class MyPainter extends CustomPainter {
@override
void paint(Canvas canvas, Size size) {
var paint = Paint()
..isAntiAlias = true
..strokeWidth=0.0
..invertColors=false;
Rect rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 100.0);
canvas.drawArc(rect, 0, 2*pi/4, true, paint..color=Colors.redAccent);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 100.0);
canvas.drawArc(rect, 2*pi/4, 2*pi/4, true, paint..color=Colors.blueAccent);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 100.0);
canvas.drawArc(rect, 2*pi/2, 2*pi/4, true, paint..color=Colors.grey);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 100.0);
canvas.drawArc(rect, 2*pi/4*3, 2*pi/4, true, paint..color=Colors.indigo);
}
//在实际场景中正确利用此回调可以避免重绘开销，本示例我们简单的返回true
@override
bool shouldRepaint(CustomPainter oldDelegate) => true;
}
五彩蜘蛛网
class MyPainter extends CustomPainter {
@override
void paint(Canvas canvas, Size size) {
var paint = Paint()
..isAntiAlias = true
..strokeWidth=0.0
..invertColors=false;
for(int i=0;i<10;i++){
Rect rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 100.0);
canvas.drawArc(rect, i*2*pi/10, 2*pi/10, false, paint..color=Colors.indigo);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 90.0);
canvas.drawArc(rect, i*2*pi/10, 2*pi/10, false, paint..color=Colors.grey);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 80.0);
canvas.drawArc(rect, i*2*pi/10, 2*pi/10, false, paint..color=Colors.blueAccent);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 70.0);
canvas.drawArc(rect, i*2*pi/10, 2*pi/10, false, paint..color=Colors.blue);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 60.0);
canvas.drawArc(rect, i*2*pi/10, 2*pi/10, false, paint..color=Colors.purpleAccent);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 50.0);
canvas.drawArc(rect, i*2*pi/10, 2*pi/10, false, paint..color=Colors.purple);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 40.0);
canvas.drawArc(rect, i*2*pi/10, 2*pi/10, false, paint..color=Colors.pinkAccent);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 30.0);
canvas.drawArc(rect, i*2*pi/10, 2*pi/10, false, paint..color=Colors.lightGreen);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 20.0);
canvas.drawArc(rect, i*2*pi/10, 2*pi/10, false, paint..color=Colors.cyan);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 10.0);
canvas.drawArc(rect, i*2*pi/10, 2*pi/10, false, paint..color=Colors.tealAccent);
}
}
//在实际场景中正确利用此回调可以避免重绘开销，本示例我们简单的返回true
@override
bool shouldRepaint(CustomPainter oldDelegate) => true;
}
旋转五彩扇叶
class MyPainter extends CustomPainter {
@override
void paint(Canvas canvas, Size size) {
var paint = Paint()
..isAntiAlias = true
..strokeWidth=0.0
..invertColors=false;
for(int i=0;i<10;i++){
Rect rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 100.0);
canvas.drawArc(rect, i*2*2*pi/10, 2*pi/10, false, paint..color=Colors.indigo);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 90.0);
canvas.drawArc(rect, i*2*2*pi/10, 2*pi/10, false, paint..color=Colors.grey);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 80.0);
canvas.drawArc(rect, i*2*2*pi/10, 2*pi/10, false, paint..color=Colors.blueAccent);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 70.0);
canvas.drawArc(rect, i*2*2*pi/10, 2*pi/10, false, paint..color=Colors.blue);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 60.0);
canvas.drawArc(rect, i*2*2*2*pi/10, 2*pi/10, false, paint..color=Colors.purpleAccent);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 50.0);
canvas.drawArc(rect, i*2*2*2*pi/10, 2*pi/10, false, paint..color=Colors.purple);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 40.0);
canvas.drawArc(rect, i*2*2*pi/10, 2*pi/10, false, paint..color=Colors.pinkAccent);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 30.0);
canvas.drawArc(rect, i*2*2*pi/10, 2*pi/10, false, paint..color=Colors.lightGreen);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 20.0);
canvas.drawArc(rect, i*2*2*pi/10, 2*pi/10, false, paint..color=Colors.cyan);
rect=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: 10.0);
canvas.drawArc(rect, i*2*2*pi/10, 2*pi/10, false, paint..color=Colors.tealAccent);
}
}
//在实际场景中正确利用此回调可以避免重绘开销，本示例我们简单的返回true
@override
bool shouldRepaint(CustomPainter oldDelegate) => true;
}