Canves基本操作（path简单路径绘制）

path常用的方法简介

path字面意思就是路径，在画布上绘制各种满足自己要求的图形图案

API	API介绍
lineTo	绘制直线，**起点 **为上次绘制的最后一个点，不指定默认为原点，终点为lineTo的参数
moveTo	将下次绘制的起点，移动到指定的位置，不影响之前的操作
setLastPoint	设置上次绘制的最后一个点，移动到指定的位置，影响之前的操作
close	连接第一个点连接到最后一个点，形成一个闭合区域，如果不能形成闭合区域就不做任何操作
addRect, addRoundRect, addOval, addCircle, addPath, addArc, arcTo	添加(矩形， 圆角矩形， 椭圆， 圆， 路径， 圆弧) 到当前Path (注意addArc和arcTo的区别)
isEmpty，isRect	是否为空，是否是矩形
set	替换之前的路径
offset	对之前的绘制的路径进行偏移，不影响之后的操作
quadTo, cubicTo	二次和三次贝塞尔曲线的路径

1. lineTo绘制直线

protected void onDraw(Canvas canvas) {
       super.onDraw(canvas);
    Path path=new Path();
        //绘制第一条线
        path.lineTo(200,200);
        //绘制第二条线
        path.lineTo(400,300);
        //绘制第三条线
        path.lineTo(300,400);
        canvas.drawPath(path,paint);
        paint.setStrokeWidth(1);
        paint.setColor(Color.RED);
        canvas.drawText("(200,200)",200,200,paint);
        canvas.drawText("(400,300)",400,300,paint);
        canvas.drawText("(300,400)",300,400,paint);
    }

第一次没有指定绘制的起点，默认为原点（0.0），绘制第二条线，第三条线，没有明确规定，起点为上次绘制完的最后一个点。

2. moveTo 设置下次绘制的起点

protected void onDraw(Canvas canvas) {
       super.onDraw(canvas);
        Path path=new Path();
        path.moveTo(100,100);
        //绘制第一条线
        path.lineTo(200,200);
        //绘制第二条线
        path.moveTo(100,100);
        path.lineTo(400,300);
        //绘制第三条线
        path.moveTo(100,100);
        path.lineTo(300,400);
        canvas.drawPath(path,paint);
        paint.setStrokeWidth(1);
        paint.setColor(Color.RED);
        canvas.drawText("(100,100)",300,400,paint);
        canvas.drawText("(200,200)",200,200,paint);
        canvas.drawText("(400,300)",400,300,paint);
        canvas.drawText("(300,400)",300,400,paint);
    }

设置三条线的起点都为（100，100）

3. setLastPoint设置上次绘制的终点

 protected void onDraw(Canvas canvas) {
       super.onDraw(canvas);
        Path path=new Path();
        path.moveTo(100,100);
        //绘制第一条线
        path.lineTo(200,200);
        //绘制第二条线
        path.lineTo(400,300);
        //设置上此绘制的最后一个点
        path.setLastPoint(200,300);
        //绘制第三条线
        path.lineTo(300,400);
        canvas.drawPath(path,paint);
        //绘制坐标文字
        paint.setStrokeWidth(1);
        paint.setColor(Color.RED);
        canvas.drawText("(100,100)",100,100,paint);
        canvas.drawText("(200,200)",200,200,paint);
        canvas.drawText("(400,300)",400,300,paint);
        canvas.drawText("(300,400)",300,400,paint);
        canvas.drawText("(200,300)",200,300,paint);
        //绘制坐标点
        paint.setColor(Color.GREEN);
        paint.setStrokeWidth(10);
        canvas.drawPoint(300,400,paint);
        canvas.drawPoint(400,300,paint);
        canvas.drawPoint(200,200,paint);
        canvas.drawPoint(100,100,paint);
        canvas.drawPoint(200,300,paint);
    }

在绘制完第三条线后，设置 path.setLastPoint(200,300)，发现原本第二条线是连接到（400，300）上，设置setLastPoint后连接到（200，300）上，会影响上之前的一次的绘制。

4. close 连接第一个点连接到最后一个点，形成一个闭合区域

 protected void onDraw(Canvas canvas) {
       super.onDraw(canvas);
        Path path=new Path();
        path.moveTo(100,100);
        //绘制第一条线
        path.lineTo(200,200);
        //绘制第二条线
        path.lineTo(400,300);
        //设置上此绘制的最后一个点
        path.setLastPoint(200,300);
        //绘制第三条线
        path.lineTo(300,400);
        //闭合路径
        path.close();
        canvas.drawPath(path,paint);

        //绘制坐标文字
        paint.setStrokeWidth(1);
        paint.setColor(Color.RED);
        canvas.drawText("(100,100)",100,100,paint);
        canvas.drawText("(200,200)",200,200,paint);
        canvas.drawText("(400,300)",400,300,paint);
        canvas.drawText("(300,400)",300,400,paint);
        canvas.drawText("(200,300)",200,300,paint);
        //绘制坐标点
        paint.setColor(Color.GREEN);
        paint.setStrokeWidth(10);
        canvas.drawPoint(300,400,paint);
        canvas.drawPoint(400,300,paint);
        canvas.drawPoint(200,200,paint);
        canvas.drawPoint(100,100,paint);
        canvas.drawPoint(200,300,paint);
    }

5. 添加内容到路径

5.1 添加addRect 矩形

 protected void onDraw(Canvas canvas) {
       super.onDraw(canvas);
//       initgrid(canvas);
        paint.setColor(Color.BLUE);
        Path path=new Path();
        path.moveTo(100,100);
        //绘制第一条线
        path.lineTo(200,200);
        RectF rect=new RectF(200,200,400,400);
        path.addRect(rect,Path.Direction.CCW);
        canvas.drawPath(path,paint);
    }

##### 5.2 添加addRoundRect 圆角矩形

 protected void onDraw(Canvas canvas) {
       super.onDraw(canvas);
//       initgrid(canvas);
        paint.setColor(Color.BLUE);
        Path path=new Path();
        path.moveTo(100,100);
        //绘制第一条线
        path.lineTo(200,200);
        RectF rect=new RectF(200,200,400,400);
        path.addRoundRect(rect,50,50,Path.Direction.CCW);
        canvas.drawPath(path,paint);
    }

5.3 添加addOval椭圆

 protected void onDraw(Canvas canvas) {
       super.onDraw(canvas);
//       initgrid(canvas);
        paint.setColor(Color.BLUE);
        Path path=new Path();
        path.moveTo(100,100);
        //绘制第一条线
        path.lineTo(200,200);
        RectF rect=new RectF(200,200,400,400);
        path.addOval(rect,Path.Direction.CCW);
        canvas.drawPath(path,paint);
    }

5.4 添加addCircle圆

 protected void onDraw(Canvas canvas) {
       super.onDraw(canvas);
//       initgrid(canvas);
        paint.setColor(Color.BLUE);
        Path path=new Path();
        path.moveTo(100,100);
        //绘制第一条线
        path.lineTo(200,200);
        path.addCircle(100,100,50,Path.Direction.CCW);
        canvas.drawPath(path,paint);
    }

5.5 添加addPath路径

protected void onDraw(Canvas canvas) {
       super.onDraw(canvas);
//       initgrid(canvas);
        paint.setColor(Color.BLUE);
        Path path=new Path();
        path.moveTo(100,100);
        //绘制第一条线
        path.lineTo(200,200);
        Path path1=new Path();
        path1.addCircle(100,100,50,Path.Direction.CCW);
        path.addPath(path1);
        canvas.drawPath(path,paint);
    }

5.5 添加addArc圆弧

 protected void onDraw(Canvas canvas) {
       super.onDraw(canvas);
//       initgrid(canvas);
        paint.setColor(Color.BLUE);
        Path path=new Path();
        path.moveTo(100,100);
        //绘制第一条线
        path.lineTo(200,200);
        RectF rect=new RectF(200,200,400,400);
        path.addArc(rect,30,90);
        canvas.drawPath(path,paint);
        canvas.drawRect(rect,paint);
    }

5.6 添加arcTo圆弧

 protected void onDraw(Canvas canvas) {
       super.onDraw(canvas);
//       initgrid(canvas);
        paint.setColor(Color.BLUE);
        Path path=new Path();
        path.moveTo(100,100);
        //绘制第一条线
        path.lineTo(200,200);
        RectF rect=new RectF(200,200,400,400);
        path.arcTo(rect,30,90);
        canvas.drawPath(path,paint);
        canvas.drawRect(rect,paint);
    }

注意和addArc的区别，arcTo连接上次绘制的终点

6.贝塞尔曲线

具体概念描述 https://www.jianshu.com/p/8f82db9556d2

6.1 二阶贝塞尔曲线

 protected void onDraw(Canvas canvas) {
       super.onDraw(canvas);
        paint.setColor(Color.BLUE);
        Path path=new Path();
        Path path1=new Path();
        path.moveTo(200,200);
        //绘制第一条线
        path.quadTo(150,100,400,200);
        canvas.drawPath(path,paint);
        canvas.drawPoint(200,200,xyPaint);
        canvas.drawPoint(150,100,xyPaint);
        canvas.drawPoint(400,200,xyPaint);
        path1.moveTo(200,200);
        path1.lineTo(150,100);
        path1.lineTo(400,200);
        canvas.drawPath(path1,paint);
        paint.setStrokeWidth(1);
        canvas.drawText("A(200,200)",200,200,paint);
        canvas.drawText("B(150,100)",150,100,paint);
        canvas.drawText("C(400,200)",400,200,paint);
    }

6.2 三阶贝塞尔曲线

 protected void onDraw(Canvas canvas) {
       super.onDraw(canvas);
        paint.setColor(Color.BLUE);
        Path path=new Path();
        Path path1=new Path();
        path.moveTo(200,200);
        //绘制三阶
//        path.quadTo(150,100,400,200);
        path.cubicTo(200,100,400,100,400,400);
        canvas.drawPath(path,paint);
        canvas.drawPoint(200,200,xyPaint);
        canvas.drawPoint(200,100,xyPaint);
        canvas.drawPoint(100,400,xyPaint);
        canvas.drawPoint(400,400,xyPaint);
        path1.moveTo(200,200);
        path1.lineTo(200,100);
        path1.lineTo(400,100);
        path1.lineTo(400,400);
        canvas.drawPath(path1,paint);
        paint.setStrokeWidth(1);
        canvas.drawText("A(200,200)",200,200,paint);
        canvas.drawText("B(200,100)",200,100,paint);
        canvas.drawText("C(400,100)",400,100,paint);
        canvas.drawText("D(400,400)",400,400,paint);
    }