Android自定义View之Paint

1、Paint画笔

Paint是画笔，是自定义View中最基本的东西。下面是它的一些相关Api。

 		val mPaint: Paint = Paint() //新建画笔
        mPaint.color = Color.RED //设置颜色
        mPaint.setARGB(255, 255, 255, 0)//设置Paint对象颜色，范围为0-255
        mPaint.alpha = 200 //设置alpha不透明度，范围为0-255
        mPaint.isAntiAlias = true //抗锯齿
        mPaint.style = Paint.Style.STROKE //描边效果，FILL填充，FILL_AND_STROKE填充与描边
        mPaint.strokeWidth = 4f //描边宽度
        mPaint.strokeCap = Paint.Cap.ROUND //圆角效果，SQUARE方形，
        mPaint.strokeJoin = Paint.Join.MITER //拐角风格
        mPaint.shader = SweepGradient(200f, 200f, Color.BLUE, Color.RED)//设置扫描渲染器
        mPaint.xfermode = PorterDuffXfermode(PorterDuff.Mode.DARKEN)//设置图层混合模式
        mPaint.colorFilter = LightingColorFilter(0x00ffff, 0x000000)
        mPaint.isFilterBitmap = true //设置双线性过滤
        mPaint.maskFilter = BlurMaskFilter(10f, BlurMaskFilter.Blur.NORMAL)//设置画笔遮罩滤镜，传入度数和样式
        mPaint.textScaleX = 2f //设置文本缩放倍数
        mPaint.textSize = 38f //设置字体大小
        mPaint.textAlign = Paint.Align.LEFT //对其方式，LEFT左、CENTER中、RIGHT右
        mPaint.isUnderlineText = true //设置下划线

        val str = "Android"
        val rect = Rect()
        mPaint.getTextBounds(str, 0, str.length, rect)//测量文本大小，将文本大小信息存放在Rect中
        mPaint.measureText(str)//获取文本的宽