PathMeasure,Path的测量

概念

路径测量，用来测量Path的类。

常用API

path长度测量、path跳转、path片段获取等。

1、长度测量

        var path = Path()
        path.lineTo(0f, 200f)
        path.lineTo(200f, 200f)
        path.lineTo(200f, 0f)

        canvas?.drawPath(path, paint)

        var pathMeasure = PathMeasure()
        //测量path长度，第二个参数forceClosed代表是否强制path闭合的长度
        pathMeasure.setPath(path, true)

        println("path length=${pathMeasure.length}")

        var pm2 = PathMeasure(path, false)
        println("path length = ${pm2.length}")
        
        //如果path发生了变化，PathMeasure需要重新设定path
        path.lineTo(200f,-200f)
        pm2.setPath(path,false)

2、截取一段path

        var path = Path()
        path.addRect(-200f,-200f,200f,200f,Path.Direction.CW)

        var pathDst = Path()

        var pathMeasure = PathMeasure(path,false)
        //截取path的一段到dstpath中
        pathMeasure.getSegment(200f,1000f,pathDst,true)

        canvas?.drawPath(path,paint)
        canvas?.drawPath(pathDst,linePaint)

3、path跳转

        var path = Path()
        path.addRect(-100f,-100f,100f,100f,Path.Direction.CW)
        path.addOval(-200f,-200f,200f,200f,Path.Direction.CW)
        canvas?.drawPath(path,paint)

        var pathMeasure = PathMeasure()
        pathMeasure.setPath(path,false)
        //计算的只是前一个矩形的长度
        //pathmeasure计算的只是当前path的长度，而不是整个path的长度
        println("path length=${pathMeasure.length}")
        //计算下一个圆形的长度
        pathMeasure.nextContour()
        println("path length=${pathMeasure.length}")

path长度计算

4、得到path上的点和切线斜率getPosTan()

        var path = Path()
        path.addCircle(0f, 0f, 200f, Path.Direction.CW)
        canvas?.drawPath(path, paint)

        var pos = FloatArray(2)
        var tan = FloatArray(2)
        var pathMeasure = PathMeasure(path, false)
        var distance = 0f
        //返回pos和tan，
        // distance代表在与起始点距离为distance的点的坐标
        // pos是这个点的坐标
        // tan是这个点的斜率，可以算出斜率直线和x轴的夹角
        pathMeasure.getPosTan(distance, pos, tan)
        for (p in pos)
            println("pos = $p")
        for (t in tan)
            println("tan = $t")

        canvas?.drawCircle(pos[0], pos[1], 10f, paint)
        //计算切线和x轴的夹角
        var angle = Math.toDegrees(Math.atan2(tan[1].toDouble(), tan[0].toDouble()))
        println("angle=$angle")


        distance = pathMeasure.length / 8f
        pathMeasure.getPosTan(distance, pos, tan)
        for (p in pos)
            println("pos = $p")
        for (t in tan)
            println("tan = $t")

        paint.color = Color.RED
        canvas?.drawCircle(pos[0], pos[1], 10f, paint)
        angle = Math.toDegrees(Math.atan2(tan[1].toDouble(), tan[0].toDouble()))
        println("angle=$angle")

拿到角度的作用：

        matrixx = Matrix()

        var options = BitmapFactory.Options()
        options.inSampleSize = 8
        bitmap = BitmapFactory.decodeResource(resources, R.mipmap.lyf, options)

        var path = Path()
        path.addCircle(0f, 0f, 200f, Path.Direction.CW)
        canvas?.drawPath(path, paint)

        var pos = FloatArray(2)
        var tan = FloatArray(2)
        var pathMeasure = PathMeasure(path, false)
        var distance = 0f
        //返回pos和tan，
        // distance代表在与起始点距离为distance的点的坐标
        // pos是这个点的坐标
        // tan是这个点的斜率，可以算出斜率直线和x轴的夹角
        pathMeasure.getPosTan(distance, pos, tan)
        //计算切线和x轴的夹角
        var angle = Math.toDegrees(Math.atan2(tan[1].toDouble(), tan[0].toDouble()))
        matrixx.reset()
        //进行角度旋转
        matrixx.postRotate(angle.toFloat())
        //进行位移
        matrixx.postTranslate(pos[0] - bitmap.width / 2, pos[1] - bitmap.height / 2)
        canvas?.drawBitmap(bitmap,matrixx,paint)

4、将pos和tan放到matrix里返回：getMatrix()

        var path = Path()
        path.addCircle(0f, 0f, 200f, Path.Direction.CW)
        canvas?.drawPath(path, paint)
        var pathMeasure = PathMeasure(path, false)
        //将pos和tan信息都保存在matrix中
        pathMeasure.getMatrix(
            0f,
            matrixx,
            PathMeasure.POSITION_MATRIX_FLAG or PathMeasure.TANGENT_MATRIX_FLAG
        )
        //将图片旋转中心放到图片中心位置
        matrixx.preTranslate(-bitmap.width/2f,-bitmap.height/2f)
        canvas?.drawBitmap(bitmap, matrixx, paint)