Android使用PorterDuffXfermode的模式PorterDuff.Mode.SRC_OUT实现橡皮擦，Kotlin（1）
import android.content.Context
import android.graphics.Bitmap
import android.graphics.BitmapFactory
import android.graphics.Canvas
import android.graphics.Paint
import android.graphics.Path
import android.graphics.PorterDuff
import android.graphics.PorterDuffXfermode
import android.util.AttributeSet
import android.view.MotionEvent
import androidx.appcompat.widget.AppCompatImageViewclass MyView : AppCompatImageView {private var WIDTH = 0private var HEIGHT = 0private var mPaint: Paint = Paint()private var mBmpDst: Bitmapprivate var mBmpSrc: Bitmapprivate var mPath: Pathprivate var mPreX = 0fprivate var mPreY = 0fprivate var mPorterDuffXfermode: PorterDuffXfermodeconstructor(ctx: Context, attributeSet: AttributeSet) : super(ctx, attributeSet) {//WIDTH = resources.displayMetrics.widthPixels//HEIGHT = resources.displayMetrics.heightPixels//mPaint?.setColor(Color.RED)mPaint.style = Paint.Style.STROKEmPaint.strokeWidth = 30fmBmpSrc = BitmapFactory.decodeResource(resources, R.mipmap.pic, null)WIDTH = mBmpSrc.widthHEIGHT = mBmpSrc.height//空BitmapmBmpDst = Bitmap.createBitmap(WIDTH, HEIGHT, Bitmap.Config.ARGB_8888)mPath = Path()/**** SRC_OUT** 当目标图像有图像时合成结果为空白像素;* 当目标图像没有图像时，合成结果显示源图像;* 如果把手指Path做为目标图像，在与源图像合成时，有手指轨迹的地方就变为空白像素，效果就是擦除。**/mPorterDuffXfermode = PorterDuffXfermode(PorterDuff.Mode.SRC_OUT)}override fun onDraw(canvas: Canvas) {//super.onDraw(canvas)val layerId = canvas.saveLayer(0f, 0f, WIDTH.toFloat(), HEIGHT.toFloat(), null)//绘制Pathval c = Canvas(mBmpDst)c.drawPath(mPath, mPaint)//绘制目标图像canvas.drawBitmap(mBmpDst, 0f, 0f, mPaint)//合成图像mPaint.setXfermode(mPorterDuffXfermode)canvas.drawBitmap(mBmpSrc, 0f, 0f, mPaint)mPaint.setXfermode(null)canvas.restoreToCount(layerId)}override fun onTouchEvent(event: MotionEvent): Boolean {when (event.action) {MotionEvent.ACTION_DOWN -> {mPath.moveTo(event.x, event.y)mPreX = event.xmPreY = event.yreturn true}MotionEvent.ACTION_MOVE -> {val endX = (mPreX + event.x) / 2val endY = (mPreY + event.y) / 2mPath.quadTo(mPreX, mPreY, endX, endY)mPreX = event.xmPreY = event.y}MotionEvent.ACTION_UP -> {}}postInvalidate()return super.onTouchEvent(event)}
}
手指在屏幕上滑动，图像像被橡皮擦擦掉一样。
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