需要掌握的内容

1. 难度应该大多都在数学的三角函数中，如果对这个知识点有问题的可以自行去学习一下

   
   直角三角形.png

• sin角度=a/c
• cos角度=b/c
• tan角度=a/b
• cot角度=b/a
• sec角度=c/b
• csc角度=c/a

2. 数学坐标系和Android坐标系的区别

   
   数学坐标系.png
   

   y轴朝上是+，x轴朝右是+

   
   Android坐标系.png
   x轴朝右是+，y轴朝下是+

Demo代码

class LinePathView : View{
    //坐标轴的paint
    val paint: Paint=Paint()
        val path: Path=Path()
        //贝塞尔曲线的画笔
    val pPaint:Paint=Paint()
        lateinit var center:PointF
        constructor(context: Context) : super(context){
        init()
    }
    constructor(context: Context, attrs: AttributeSet?) : super(context, attrs){
        init()
    }
    constructor(context: Context, attrs: AttributeSet?, defStyleAttr: int) : super(
            context,
            attrs,
            defStyleAttr
        ){
        init()
    }
    private fun init() {
        paint.isAntiAlias=true
                paint.isDither=true
                paint.color=Color.BLACK
                paint.strokeWidth=3f
                paint.style=Paint.Style.FILL
                pPaint.isAntiAlias=true
                pPaint.isDither=true
                pPaint.color=Color.RED
                pPaint.strokeWidth=3f
            }
            override fun onSizeChanged(w: int, h: int, oldw: int, oldh: int) {
            super.onSizeChanged(w, h, oldw, oldh)
                    center=PointF((measuredWidth/2).tofloat(), (measuredHeight/2).tofloat())
        }
        override fun onDraw(canvas: Canvas) {
            super.onDraw(canvas)
                    canvas.drawLine((measuredWidth/2).tofloat(), 0F, (measuredWidth/2).tofloat(),
                        measuredHeight.tofloat(),paint)
                    canvas.drawLine(0f,(measuredHeight/2).tofloat(),  measuredWidth.tofloat(),
                        (measuredHeight/2).tofloat(),paint)
                    //计算x轴上顶点的坐标
            val top = calPoint(center, (measuredHeight / 2).tofloat(), 90F)
                    val rightTop = calPoint(top, 80f, -45f)
                    canvas.drawLine(top.x,top.y,rightTop.x,rightTop.y,paint)
                    val leftTop = calPoint(top, 80f, -135f)
                    canvas.drawLine(top.x,top.y,leftTop.x,leftTop.y,paint)
                    //计算y轴右顶点的坐标
            val rightY = calPoint(center, (measuredWidth / 2).tofloat(), 360F)
                    val yTopLeft = calPoint(rightY, 80f, 135f)
                    canvas.drawLine(rightY.x,rightY.y,yTopLeft.x,yTopLeft.y,paint)
                    val yTopRight = calPoint(rightY, 80f, -135f)
                    canvas.drawLine(rightY.x,rightY.y,yTopRight.x,yTopRight.y,paint)
                    //计算贝塞尔曲线的一段的终点坐标(起点是中心点)
            val lastPoint = calPoint(center, 200f, 0f)
                    //计算贝塞尔曲线控制点的坐标
            val controlPoint = calPoint(center, 200f, 60f)
                    path.reset()
                    path.moveTo(center.x,center.y)
                    path.quadTo(controlPoint.x,controlPoint.y,lastPoint.x,lastPoint.y)
                    canvas.drawPath(path,pPaint)
                    //根据第一个贝塞尔曲线的终点画第二个
            val secondLastPoint = calPoint(lastPoint, 200f, 0f)
                    //第二个贝塞尔曲线的控制点
            val secondControl = calPoint(lastPoint, 200f, -60f)
                    path.reset()
                    path.moveTo(lastPoint.x,lastPoint.y)
                    path.quadTo(secondControl.x,secondControl.y,secondLastPoint.x,secondLastPoint.y)
                    canvas.drawPath(path,pPaint)
                    //绘制梯形(以中心点为坐标在第二象限找一个点作为梯形底边的一个顶点)
            val rightBottomPoint = calPoint(center, 200f, 135f)
                    val leftBottomPoint = calPoint(rightBottomPoint, 300f, -180f)
                    val leftTopPoint = calPoint(leftBottomPoint, 80f, 45f)
                    val rightTopPoint = calPoint(leftTopPoint, 200f, 0f)
                    path.reset()
                    path.moveTo(rightBottomPoint.x,rightBottomPoint.y)
                    path.lineTo(leftBottomPoint.x,leftBottomPoint.y)
                    path.lineTo(leftTopPoint.x,leftTopPoint.y)
                    path.lineTo(rightTopPoint.x,rightTopPoint.y)
                    canvas.drawPath(path,pPaint)
                    //在第三象限找一个点作为三角形的顶点
            val sanTopPoint = calPoint(center, 300f, -135f)
                    val sanRightBottom = calPoint(sanTopPoint, 200f, -45f)
                    val sanLeftBottom = calPoint(sanRightBottom, 300f, 180f)
                    path.reset()
                    path.moveTo(sanTopPoint.x,sanTopPoint.y)
                    path.lineTo(sanLeftBottom.x,sanLeftBottom.y)
                    path.lineTo(sanRightBottom.x,sanRightBottom.y)
                    canvas.drawPath(path,pPaint)
        }
        fun calPoint(start: PointF,lineLength: float,angel: float): PointF {
            //根据角度的cos值和斜边的长度求出相邻边的长度，也就是x的偏移量
            val x:float= (Math.cos(Math.toRadians(angel.todouble()))*lineLength).tofloat()
                    //根据角度的sin值和斜边的长度求出相对边的长度，也就是y的偏移量
            val y:float= (Math.sin(Math.toRadians(angel.todouble()-180))*lineLength).tofloat()
                    return PointF(start.x+x,start.y+y)
        }
    }

运行结果

可能有点丑，但是只要内部原理知道了，花点时间可以自己调一下角度和线的长度。

运行结果.png