Flutter 画笔(Paint)、drawRect(绘制矩形)、PaintingStyle

                

      

drawRect(rect, paint)

rect	矩形
paint	画笔

 

PaintingStyle.fill（用画笔填充绘制）

Rect.fromCircle({ Offset center, double radius }) : this.fromCenter(
    center: center,
    width: radius * 2,
    height: radius * 2,
  );

 

class MyPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    var paint = Paint()
      ..isAntiAlias = true
      ..strokeWidth=1.0
      ..style=PaintingStyle.fill
      ..color=Colors.green
      ..invertColors=false;
    double cx=size.width/2,cy=size.height/2;
    double radius=size.width/4;
    Rect rect=Rect.fromCircle(center: Offset(cx,cy),radius: radius);
    canvas.drawRect(rect, 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
      ..style=PaintingStyle.fill
      ..color=Colors.green
      ..invertColors=false;
    Rect rect=Rect.fromLTRB(50.0, 50.0, size.width-50.0, size.height-200.0);
    canvas.drawRect(rect, 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
      ..style=PaintingStyle.fill
      ..color=Colors.green
      ..invertColors=false;
    Rect rect=Rect.fromPoints(Offset(size.width/2, 0), Offset(0.0, size.height/2));
    canvas.drawRect(rect, paint);

     rect=Rect.fromPoints(Offset(size.width/3, 0), Offset(0.0, size.height/3));
    canvas.drawRect(rect, paint..color=Colors.red);

    rect=Rect.fromPoints(Offset(0, 0), Offset(size.width/4, size.height/4));
    canvas.drawRect(rect, 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;
}

 

const Rect.fromLTWH(double left, double top, double width, double height) : 

this.fromLTRB(left, top, left + width, top + height);

left	左边相对于原点的偏移量
top	顶部相对于原点的偏移量
width	矩形的宽度
height	矩形高度

 

class MyPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    var paint = Paint()
      ..isAntiAlias = true
      ..strokeWidth=1.0
      ..style=PaintingStyle.fill
      ..color=Colors.green
      ..invertColors=false;
    Rect rect=Rect.fromLTWH(50.0, 50.0, size.width/2, size.height/2);
    canvas.drawRect(rect, 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 }) : this.fromLTRB(
    center.dx - width / 2,
    center.dy - height / 2,
    center.dx + width / 2,
    center.dy + height / 2,
  );

center	矩形中心坐标点
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=1.0
      ..style=PaintingStyle.fill
      ..color=Colors.green
      ..invertColors=false;
    Rect rect=Rect.fromCenter(center: Offset(size.width/2,size.height/2),
width:size.width/2,height:size.height/2);
    canvas.drawRect(rect, 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
      ..style=PaintingStyle.fill
      ..color=Colors.green
      ..invertColors=false;
    Rect a=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: size.width/2);
    Rect b=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: size.width/3);
    Rect rect=Rect.lerp(a, b, 0.5);

    canvas.drawRect(a, paint..color=Colors.red);

    canvas.drawRect(rect, paint..color=Colors.grey);

    canvas.drawRect(b, paint..color=Colors.green);
  }

  //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;
}

 

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;
}

PaintingStyle.fill（用画笔绘制边框）

class MyPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    var paint = Paint()
      ..isAntiAlias = true
      ..strokeWidth=1.0
      ..style=PaintingStyle.stroke
      ..color=Colors.green
      ..invertColors=false;
    Rect a=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: size.width/2);
    Rect b=Rect.fromCircle(center: Offset(size.width/2,size.height/2),radius: size.width/3);
    Rect rect=Rect.lerp(a, b, 0.5);

    canvas.drawRect(a, paint..color=Colors.red);

    canvas.drawRect(rect, paint..color=Colors.grey);

    canvas.drawRect(b, paint..color=Colors.green);
  }

  //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
      ..style=PaintingStyle.stroke
      ..color=Colors.green
      ..invertColors=false;
    double cx=size.width/2,cy=size.height/2;
    double radius=size.width/4;
    Rect rect=Rect.fromCircle(center: Offset(cx,cy),radius: radius);
    canvas.drawRect(rect, 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
      ..style=PaintingStyle.stroke
      ..color=Colors.green
      ..invertColors=false;
    Rect rect=Rect.fromPoints(Offset(size.width/2, 0), Offset(0.0, size.height/2));
    canvas.drawRect(rect, paint);

    rect=Rect.fromPoints(Offset(size.width/3, 0), Offset(0.0, size.height/3));
    canvas.drawRect(rect, paint..color=Colors.red);

    rect=Rect.fromPoints(Offset(0, 0), Offset(size.width/4, size.height/4));
    canvas.drawRect(rect, 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;
}

 俄罗斯方块的一面

class MyPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    var paint = Paint()
      ..isAntiAlias = true
      ..strokeWidth = 1.0
      ..style = PaintingStyle.fill
      ..color = Colors.green
      ..invertColors = false;

    double w = size.width / 3;
    double h = size.height / 3;
    for (int i = 0; i < 3; i++) {
      for (int j = 0; j < 3; j++) {
        Rect rect = Rect.fromPoints(
            Offset(w * j, h * i), Offset(w * (j + 1), h * (i + 1)));
        switch (i) {
          case 0:
            canvas.drawRect(rect, paint..color = (i % 2 == 0 &&j%2==0? Colors.blue : Colors.deepOrange));
            break;
          case 1:
            canvas.drawRect(rect, paint..color = (i % 3 == 1 &&j%3==0? Colors.red : Colors.green));
            break;
          case 2:
            canvas.drawRect(rect, paint..color = (i % 2 == 0 && j%2==0? Colors.amber : Colors.deepPurpleAccent));
            break;
        }
      }
    }
  }

  //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
      ..style = PaintingStyle.fill
      ..color = Colors.green
      ..invertColors = false;

    double w = size.width / 3;
    double h = size.height / 3;
    for (int i = 0; i < 3; i++) {
      for (int j = 0; j < 3; j++) {
        Rect rect = Rect.fromPoints(
            Offset(w * j, h * i), Offset(w * (j + 1), h * (i + 1)));
        switch (i) {
          case 0:
            canvas.drawRect(rect, paint..color = (i % 2 == 0 &&j%2==0? Colors.blue : Colors.deepOrange));
            break;
          case 1:
            canvas.drawRect(rect, paint..color = (i % 3 == 1 &&j%3==1? Colors.red : Colors.green));
            break;
          case 2:
            canvas.drawRect(rect, paint..color = (i % 2 == 0 &&j%2==0? Colors.amber : Colors.deepPurpleAccent));
            break;
        }
      }
    }
  }

  //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;
}

五彩网格

 

class MyPainter extends CustomPainter {
  @override
  void paint(Canvas canvas, Size size) {
    var paint = Paint()
      ..isAntiAlias = true
      ..strokeWidth = 1.0
      ..style = PaintingStyle.stroke
      ..color = Colors.green
      ..invertColors = false;

    double w = size.width / 9;
    double h = size.height / 9;
    for (int i = 0; i < 9; i++) {
      for (int j = 0; j < 9; j++) {
        Rect rect = Rect.fromPoints(
            Offset(w * j, h * i), Offset(w * (j + 1), h * (i + 1)));
        switch (i) {
          case 0:
          case 8:
          case 6:
            canvas.drawRect(rect, paint..color = (i % 2 == 0 &&j%2==0? Colors.blue : Colors.deepOrange));
            break;
          case 1:
          case 3:
          case 5:
            canvas.drawRect(rect, paint..color = (i % 3 == 1 &&j%3==1? Colors.red : Colors.green));
            break;
          case 2:
          case 7:
          case 4:
            canvas.drawRect(rect, paint..color = (i % 2 == 0 &&j%2==0? Colors.amber : Colors.deepPurpleAccent));
            break;
        }
      }
    }
  }

  //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
      ..style = PaintingStyle.fill
      ..color = Colors.green
      ..invertColors = false;

    double w = size.width / 9;
    double h = size.height / 9;
    for (int i = 0; i < 9; i++) {
      for (int j = 0; j < 9; j++) {
        Rect rect = Rect.fromPoints(
            Offset(w * j, h * i), Offset(w * (j + 1), h * (i + 1)));
        switch (i) {
          case 0:
          case 8:
          case 6:
            canvas.drawRect(rect, paint..color = (i % 2 == 0 &&j%2==0? Colors.blue : Colors.deepOrange));
            break;
          case 1:
          case 3:
          case 5:
            canvas.drawRect(rect, paint..color = (i % 3 == 1 &&j%3==1? Colors.red : Colors.green));
            break;
          case 2:
          case 7:
          case 4:
            canvas.drawRect(rect, paint..color = (i % 2 == 0 &&j%2==0? Colors.amber : Colors.deepPurpleAccent));
            break;
        }
      }
    }
  }

  //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;
}