Android BitmapShader更简易的实现刮刮乐功能，Kotlin

比这种方式 Android使用PorterDuffXfermode模式PorterDuff.Mode.SRC_OUT橡皮擦实现"刮刮乐"效果，Kotlin（2）-CSDN博客

更简单实现刮刮乐效果。

Kotlin 复制代码

import android.content.Context
import android.graphics.BitmapFactory
import android.graphics.BitmapShader
import android.graphics.Canvas
import android.graphics.Paint
import android.graphics.Path
import android.graphics.Shader
import android.util.AttributeSet
import android.view.MotionEvent
import androidx.appcompat.widget.AppCompatImageView

class MyView : AppCompatImageView {
    private var mPaint: Paint = Paint()
    private var mPath: Path = Path()
    private var mPreX = 0f
    private var mPreY = 0f
    private var mBitmapShader: BitmapShader? = null

    private val mResId = R.mipmap.p

    constructor(ctx: Context, attributeSet: AttributeSet) : super(ctx, attributeSet) {
        mPaint.style = Paint.Style.STROKE
        mPaint.strokeWidth = 50f

        val bmp = BitmapFactory.decodeResource(resources, mResId, null)
        mBitmapShader = BitmapShader(bmp, Shader.TileMode.CLAMP, Shader.TileMode.REPEAT)

        mPaint.setShader(mBitmapShader)
    }

    override fun onDraw(canvas: Canvas) {
        super.onDraw(canvas)

        canvas.drawPath(mPath, mPaint)
    }

    override fun onTouchEvent(event: MotionEvent): Boolean {
        when (event.action) {
            MotionEvent.ACTION_DOWN -> {
                mPath.moveTo(event.x, event.y)
                mPreX = event.x
                mPreY = event.y

                return true
            }

            MotionEvent.ACTION_MOVE -> {
                val endX = (mPreX + event.x) / 2
                val endY = (mPreY + event.y) / 2
                mPath.quadTo(mPreX, mPreY, endX, endY)

                mPreX = event.x
                mPreY = event.y
            }

            MotionEvent.ACTION_UP -> {

            }
        }

        postInvalidate()

        return super.onTouchEvent(event)
    }
}

进入后首先是红色，随着手指在屏幕上划过，原图出现。