??????小菜最近在學(xué)習(xí)自定義 View，剛了解了一下 Paint 畫筆的神奇之處，現(xiàn)在學(xué)習(xí)一下 Canvas 畫布的神秘之處。Flutter 提供了眾多的繪制方法，小菜接觸不深，盡量都嘗試一下。

Canvas 畫布

drawColor 繪制背景色

??????drawColor 需要傳入兩個參數(shù)，第一個為色值，第二個為混合模式，有眾多混合模式供選擇，但注意使用混合模式后會與繪制其上的其他 View 顏色混合像素。

canvas.drawColor(Colors.pinkAccent, BlendMode.srcIn);

drawPoints 繪制點/線

??????drawPoints 不僅可以繪制點，還可以繪制點與點的連線；PointMode 包括 points 點 / lines 線 / polygon 多邊形；注意 lines 為每兩點之間的連線，若為奇數(shù)個點，最后一個沒有與之相連的點。

// 繪制點 canvas.drawPoints(PointMode.points,[Offset(30.0, 30.0), Offset(60.0, 30.0),Offset(90.0, 30.0), Offset(90.0, 60.0),Offset(60.0, 60.0), Offset(30.0, 60.0)],Paint()..strokeWidth = 4.0); canvas.drawPoints(PointMode.points,[Offset(160.0, 30.0), Offset(190.0, 30.0),Offset(220.0, 30.0), Offset(220.0, 60.0),Offset(190.0, 60.0), Offset(160.0, 60.0)],Paint()..strokeWidth = 4.0..strokeCap = StrokeCap.round); // 繪制線 canvas.drawPoints(PointMode.lines,[Offset(30.0, 100.0), Offset(60.0, 100.0),Offset(90.0, 100.0), Offset(90.0, 130.0),Offset(60.0, 130.0), Offset(30.0, 130.0)],Paint()..strokeWidth = 4.0..strokeCap = StrokeCap.round); // 繪制多邊形 canvas.drawPoints(PointMode.polygon,[Offset(160.0, 100.0), Offset(190.0, 100.0),Offset(220.0, 100.0), Offset(220.0, 130.0),Offset(190.0, 130.0), Offset(160.0, 130.0)],Paint()..strokeWidth = 4.0..strokeCap = StrokeCap.round);

drawLine 繪制線

canvas.drawLine(Offset(30.0, 90.0), Offset(Screen.width - 30.0, 90.0),Paint()..strokeWidth = 4.0); canvas.drawLine(Offset(30.0, 120.0), Offset(Screen.width - 30.0, 120.0),Paint()..strokeWidth = 4.0..strokeCap = StrokeCap.round); canvas.drawLine(Offset(30.0, 150.0), Offset(Screen.width - 30.0, 150.0),Paint()..strokeWidth = 4.0..strokeCap = StrokeCap.square);

drawArc 繪制弧/餅

??????drawArc 可以用來繪制圓弧甚至配合 Paint 繪制餅狀圖；drawArc 的第一個參數(shù)為矩形范圍，即圓弧所在的圓的范圍，若非正方形則圓弧所在的圓會拉伸；第二個參數(shù)為起始角度，0.0 為坐標(biāo)系 x 軸正向方形；第三個參數(shù)為終止角度，若超過 2*PI，則為一個圓；第四個參數(shù)為是否由中心出發(fā)，false 時只繪制圓弧，true 時繪制圓餅；第五個參數(shù)即 Paint 畫筆，可通過 PaintingStyle 屬性繪制是否填充等；

const PI = 3.1415926; canvas.drawArc(Rect.fromCircle(center: Offset(60.0, 60.0), radius: 80.0),0.0, PI / 2, false,Paint()..color = Colors.white..strokeCap = StrokeCap.round..strokeWidth = 4.0..style = PaintingStyle.stroke); canvas.drawArc(Rect.fromCircle(center: Offset(200.0, 60.0), radius: 80.0),0.0, PI / 2, false,Paint()..color = Colors.white..strokeWidth = 4.0..style = PaintingStyle.fill); canvas.drawArc(Rect.fromCircle(center: Offset(90.0, 160.0), radius: 80.0),0.0, PI * 2 / 3, true,Paint()..color = Colors.white..strokeWidth = 4.0..style = PaintingStyle.stroke); canvas.drawArc(Rect.fromCircle(center: Offset(250.0, 160.0), radius: 80.0),0.0, PI * 2 / 3, true,Paint()..color = Colors.white..strokeWidth = 4.0..style = PaintingStyle.fill); canvas.drawArc(Rect.fromLTWH(30.0, 300.0, 200.0, 100.0),0.0, 5.0, true,Paint()..color = Colors.white..style = PaintingStyle.fill); canvas.drawArc(Rect.fromPoints(Offset(260.0, 260.0), Offset(320.0, 420.0)),0.0, 5.0, true,Paint()..color = Colors.white..style = PaintingStyle.fill);

drawRect 繪制矩形

??????drawRect 用來繪制矩形，Flutter 提供了多種繪制矩形方法：

Rect.fromPoints 根據(jù)兩個點(左上角點/右下角點)來繪制；

Rect.fromLTRB 根據(jù)以屏幕左上角為坐標(biāo)系圓點，分別設(shè)置上下左右四個方向距離；

Rect.fromLTWH 根據(jù)設(shè)置左上角的點與矩形寬高來繪制；

Rect.fromCircle 最特殊，根據(jù)圓形繪制正方形；

canvas.drawRect(Rect.fromPoints(Offset(30.0, 30.0), Offset(150.0, 100.0)),Paint()..color = Colors.white..strokeWidth = 4.0..style = PaintingStyle.stroke); canvas.drawRect(Rect.fromPoints(Offset(210.0, 30.0), Offset(330.0, 100.0)),Paint()..color = Colors.white..style = PaintingStyle.fill); canvas.drawRect(Rect.fromLTRB(30.0, 140.0, 150.0, 210.0),Paint()..color = Colors.white); canvas.drawRect(Rect.fromLTWH(210.0, 140.0, 120.0, 70.0),Paint()..color = Colors.white); canvas.drawRect(Rect.fromCircle(center: Offset(90.0, 300.0), radius: 60.0),Paint()..color = Colors.white..strokeWidth = 4.0..style = PaintingStyle.stroke);

drawRRect 繪制圓角矩形

??????drawRRect 繪制圓角矩形，Flutter 提供了多種繪制方法：

RRect.fromLTRBXY 前四個參數(shù)用來繪制矩形位置，剩余兩個參數(shù)繪制固定 x/y 弧度；

RRect.fromLTRBR 前四個參數(shù)用來繪制矩形位置，最后一個參數(shù)繪制 Radius 弧度；

RRect.fromLTRBAndCorners 前四個參數(shù)用來繪制矩形位置，剩余四個可選擇參數(shù)，根據(jù)需求設(shè)置四個角 Radius 弧度，可不同；

RRect.fromRectXY 第一個參數(shù)繪制矩形，可以用上面介紹的多種矩形繪制方式，剩余兩個參數(shù)繪制固定 x/y 弧度；

RRect.fromRectAndRadius 第一個參數(shù)繪制矩形，可以用上面介紹的多種矩形繪制方式，最后一個參數(shù)繪制 Radius 弧度；

RRect.fromRectAndCorners第一個參數(shù)繪制矩形，可以用上面介紹的多種矩形繪制方式，剩余四個可選擇參數(shù)，根據(jù)需求設(shè)置四個角 Radius 弧度，最為靈活。

// RRect.fromLTRBXY 方式 canvas.drawRRect(RRect.fromLTRBXY(30.0, 30.0, 150.0, 100.0, 8.0, 8.0),Paint()..color = Colors.white..strokeWidth = 4.0..style = PaintingStyle.stroke); canvas.drawRRect(RRect.fromLTRBXY(210.0, 30.0, 330.0, 100.0, 8.0, 18.0),Paint()..color = Colors.white..style = PaintingStyle.fill); // RRect.fromLTRBR 方式 canvas.drawRRect(RRect.fromLTRBR(30.0, 140.0, 150.0, 210.0, Radius.circular(8.0)),Paint()..color = Colors.white..strokeWidth = 4.0..style = PaintingStyle.stroke); // RRect.fromLTRBAndCorners 方式 canvas.drawRRect(RRect.fromLTRBAndCorners(210.0, 140.0, 330.0, 210.0,topLeft: Radius.circular(5.0),topRight: Radius.circular(20.0),bottomRight: Radius.circular(5.0),bottomLeft: Radius.circular(20.0)),Paint()..color = Colors.white..strokeWidth = 4.0..style = PaintingStyle.stroke); // RRect.fromRectAndCorners 方式 canvas.drawRRect(RRect.fromRectAndCorners(Rect.fromLTWH(30.0, 260.0, 120.0, 70.0),topLeft: Radius.circular(5.0),topRight: Radius.circular(20.0),bottomRight: Radius.circular(5.0),bottomLeft: Radius.circular(20.0)),Paint()..color = Colors.white..strokeWidth = 4.0..style = PaintingStyle.stroke); // RRect.fromRectAndRadius 方式 canvas.drawRRect(RRect.fromRectAndRadius(Rect.fromLTWH(210.0, 260.0, 120.0, 70.0),Radius.elliptical(8.0, 18.0)),Paint()..color = Colors.white..strokeWidth = 4.0..style = PaintingStyle.stroke); // RRect.fromRectXY 方式 canvas.drawRRect(RRect.fromRectXY(Rect.fromCircle(center: Offset(90.0, 420.0), radius: 60.0),8.0, 8.0),Paint()..color = Colors.white..strokeWidth = 4.0..style = PaintingStyle.stroke);

drawDRRect 繪制嵌套矩形

??????drawDRRect 繪制嵌套矩形，第一個參數(shù)為外部矩形，第二個參數(shù)為內(nèi)部矩形，可用上述多種設(shè)置圓角矩形方式；最后一個參數(shù)為 Paint 畫筆，且 PaintingStyle 為 fill 時填充的是兩個矩形之間的范圍。

canvas.drawDRRect(RRect.fromRectXY(Rect.fromCircle(center: Offset(90.0, 420.0), radius: 60.0), 8.0, 8.0),RRect.fromRectXY(Rect.fromCircle(center: Offset(90.0, 420.0), radius: 54.0), 8.0, 8.0),Paint()..color = Colors.whit..strokeWidth = 3.0..style = PaintingStyle.stroke); canvas.drawDRRect(RRect.fromRectXY(Rect.fromCircle(center: Offset(270.0, 420.0), radius: 60.0), 8.0, 8.0),RRect.fromRectXY(Rect.fromCircle(center: Offset(270.0, 420.0), radius: 54.0), 8.0, 8.0),Paint()..color = Colors.white..strokeWidth = 3.0..style = PaintingStyle.fill);

drawCircle 繪制圓形

??????drawCircle 繪制圓形，僅需設(shè)置原點及半徑即可；

canvas.drawCircle(Offset(90.0, 420.0), 60.0,Paint()..color = Colors.white..strokeWidth = 3.0..style = PaintingStyle.stroke); canvas.drawCircle(Offset(270.0, 420.0), 60.0,Paint()..color = Colors.white..strokeWidth = 3.0..style = PaintingStyle.fill);

drawOval 繪制橢圓

??????drawOval 繪制橢圓方式很簡單，主要繪制一個矩形即可；

canvas.drawOval(Rect.fromLTRB(30.0, 30.0, 150.0, 100.0),Paint()..color = Colors.white..strokeWidth = 3.0..style = PaintingStyle.stroke); canvas.drawOval(Rect.fromLTRB(210.0, 30.0, 330.0, 100.0),Paint()..color = Colors.white..strokeWidth = 3.0..style = PaintingStyle.fill);

drawPath 繪制路徑

??????drawPath 用來繪制路徑，Flutter 提供了眾多路徑方法，小菜嘗試幾種常用的方法：

moveTo() 即從當(dāng)前坐標(biāo)點開始，不設(shè)置時默認(rèn)為屏幕左上角位置；

lineTo() 即從起點繪制到設(shè)置的新的點位；

close() 即最后的點到起始點連接，但對于中間繪制矩形/弧等時最后不會相連；

reset() 即清空連線；

addRect() 添加矩形連線；

addOval() 添加弧線，即貝塞爾(二階)曲線；

cubicTo() 添加弧線，即貝塞爾(三階)曲線；

relativeMoveTo() 相對于移動到當(dāng)前點位，小菜認(rèn)為與 moveTo 相比整個坐標(biāo)系移動；

relativeLineTo() 相對連接到當(dāng)前點位，并將坐標(biāo)系移動到當(dāng)前點位；

canvas.drawPath(Path()..moveTo(30.0, 100.0)..lineTo(120.0, 100.0)..lineTo(90.0, 130.0)..lineTo(180.0, 130.0)..close(),Paint()..color = Colors.white..strokeWidth = 3.0..style = PaintingStyle.stroke); canvas.drawPath(Path()..moveTo(200.0, 100.0)..lineTo(290.0, 100.0)..lineTo(260.0, 130.0)..lineTo(350.0, 130.0)..close(),Paint()..color = Colors.white..strokeWidth = 3.0..style = PaintingStyle.fill); canvas.drawPath(Path()..moveTo(30.0, 170.0)..lineTo(120.0, 170.0)..lineTo(90.0, 210.0)..lineTo(180.0, 210.0)..addRect(Rect.fromLTWH(180.0, 210.0, 120.0, 70.0))..addOval(Rect.fromLTWH(180.0, 210.0, 120.0, 70.0))..moveTo(230.0, 170.0)..lineTo(320.0, 170.0)..close(),Paint()..color = Colors.white..strokeWidth = 3.0..style = PaintingStyle.stroke); canvas.drawPath(Path()..arcTo(Rect.fromCircle(center: Offset(60, 300), radius: 80), -PI / 6,PI * 2 / 3, false),Paint()..color = Colors.white..strokeWidth = 3.0..style = PaintingStyle.stroke); canvas.drawPath(Path()..moveTo(210.0, 300.0)..cubicTo(210.0, 390.0, 270.0, 330.0, 330.0, 300.0),Paint()..color = Colors.black..strokeWidth = 3.0..style = PaintingStyle.stroke);

??????小菜繪制了一個基本的坐標(biāo)系來比較一下 moveTo()/lineTo() 與 relativeMoveTo()/relativeLineTo() 的區(qū)別：

canvas.drawPath(Path()..relativeMoveTo(30.0, 30.0)..relativeLineTo(120.0, 30.0)..relativeLineTo(90.0, 60.0)..relativeLineTo(180.0, 60.0),Paint()..color = Colors.blue..strokeWidth = 6.0..style = PaintingStyle.stroke); canvas.drawPath(Path()..moveTo(30.0, 30.0)..lineTo(120.0, 30.0)..lineTo(90.0, 60.0)..lineTo(180.0, 60.0),Paint()..color = Colors.orange..strokeWidth = 6.0..style = PaintingStyle.stroke);

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??????小菜對自定義 View 研究還不深入，有很多方法還沒有嘗試，有錯誤的地方希望多多指導(dǎo)！

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