用 canvas 绘图

Question

如何使用canvas绘制选中的蓝色背景透明色域？

在官方文档中我发现类似 this 的东西。但是还有一个问题就是如何实现。

又比如，我试着画线：

private fun someFun(canvas: Canvas, parent: RecyclerView) {
    val radius: Float = parent.context.resources.getDimension(R.dimen.dimen_12)
    val paint = Paint()
    paint.color = ContextCompat.getColor(parent.context, R.color.primary)
    paint.style = Paint.Style.FILL

    val path = Path()
    path.moveTo(0f, 0f)
    path.lineTo(0f, radius)
    path.arcTo(RectF(0f, 0f, radius * 2, radius * 2), 270f, -90f)
    path.close()
    canvas.drawPath(path, paint)
}

然后得到这样的东西：

Answer 1

决定采用下一种方式：

 private fun drawRoundedCorners(canvas: Canvas, parent: RecyclerView) {
    val radius: Float = parent.context.resources.getDimension(R.dimen.dimen_12)
    val paint = Paint()
    paint.color = ContextCompat.getColor(parent.context, R.color.primary)
    paint.style = Paint.Style.FILL

    val path = Path()
    path.moveTo(0f, 0f)
    path.lineTo(150f, 0f)
    path.arcTo(RectF(0f, 0f, radius * 2, radius * 2), 270f, -90f)

    path.moveTo(parent.width.toFloat(), 0f)
    path.lineTo(parent.width.toFloat(), 0f)
    path.arcTo(RectF(parent.width.toFloat() - radius * 2, 0f, parent.width.toFloat(),
            radius * 2), 270f, 90f)
    path.close()
    canvas.drawPath(path, paint)
}

用 canvas 绘图

Draw with canvas

android

android-canvas

kotlin