Android使用setXfermode例子

package com.cc.rxandroid

import android.content.Context
import android.graphics.*
import android.util.AttributeSet
import android.view.View


class MyView(c: Context, a: AttributeSet): View(c, a) {

    val paint = Paint()

    override fun onDraw(canvas: Canvas) {
        super.onDraw(canvas)
        setLayerType(LAYER_TYPE_SOFTWARE, null)

        paint.color = -0x33bc
        canvas.drawBitmap(makeDst(width, height), 0f, 0f, paint)

        paint.color = -0x995501
        paint.xfermode = PorterDuffXfermode(PorterDuff.Mode.SRC_IN)
        canvas.drawBitmap(makeSrc(width, height), 0f, 0f, paint)


        paint.xfermode = null
    }

    fun makeDst(w: Int, h: Int): Bitmap {
        val bm = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888)
        val canvas = Canvas(bm)
        val p = Paint(Paint.ANTI_ALIAS_FLAG)
        p.color = -0x33bc
        canvas.drawOval(RectF(0f, 0f, w * 3f / 4, h * 3f / 4), p)
        return bm
    }

    fun makeSrc(w: Int, h: Int): Bitmap {
        val bm = Bitmap.createBitmap(w, h, Bitmap.Config.ARGB_8888)
        val canvas = Canvas(bm)
        val p = Paint(Paint.ANTI_ALIAS_FLAG)
        p.color = -0x995501
        canvas.drawRect(
            (w / 3).toFloat(), (h / 3).toFloat(), (w * 19 / 20).toFloat(),
            (h * 19 / 20).toFloat(), p
        )
        return bm
    }
}

运行效果：

不使用xfermode

使用xfermode.scr_in后

官方效果示例：

有几个使用的点要注意下：

1.绘制的源图和新图必须是bitmap，才能有官方例子的效果。

2.要关闭硬件加速。