Android Canvas画布saveLayer与对应restoreToCount，Kotlin

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Android Canvas画布saveLayer与对应restoreToCount，Kotlin

    private fun mydraw() {val originBmp = BitmapFactory.decodeResource(resources, R.mipmap.pic).copy(Bitmap.Config.ARGB_8888, true)val newBmp = Bitmap.createBitmap(originBmp.width, originBmp.height, Bitmap.Config.ARGB_8888)val canvas = Canvas(newBmp)//把原图绘制在画布Canvascanvas.drawBitmap(originBmp, 0f, 0f, null)iv?.setImageURI(Uri.fromFile(saveBitmapToFile(newBmp)))val paint = Paint(Paint.ANTI_ALIAS_FLAG)paint.color = Color.REDpaint.textSize = 40fpaint.style = Paint.Style.STROKEpaint.strokeWidth = 2fpaint.textAlign = Paint.Align.LEFT//新图层，绿色背景，红色圆圈。val layer1 = canvas.saveLayer(0f, 0f, canvas.width.toFloat(), (canvas.height.toFloat() * 0.9).toFloat(), null)canvas.drawColor(Color.GREEN)canvas.drawCircle((canvas.width / 2).toFloat(), (canvas.height / 2).toFloat(), 50f, paint)canvas.restoreToCount(layer1)iv1?.setImageURI(Uri.fromFile(saveBitmapToFile(newBmp)))//新图层，灰色背景，直线。val layer2 = canvas.saveLayer(0f, 0f, canvas.width.toFloat(), (canvas.height.toFloat() * 0.8).toFloat(), null)canvas.drawColor(Color.GRAY)canvas.drawLine(canvas.width.toFloat() / 2,canvas.height.toFloat() / 2,canvas.width.toFloat(),canvas.height.toFloat(),paint)canvas.restoreToCount(layer2)iv2?.setImageURI(Uri.fromFile(saveBitmapToFile(newBmp)))//新图层，绿色背景，文字flyval layer3 = canvas.saveLayer(0f, 0f, canvas.width.toFloat(), (canvas.height.toFloat() * 0.5).toFloat(), null)canvas.drawColor(Color.BLUE)val x = 50fval y = 150fcanvas.drawText("fly", x, y, paint)canvas.restoreToCount(layer3)iv3?.setImageURI(Uri.fromFile(saveBitmapToFile(newBmp)))/*** 如果不事先把bitmap通过文件形式存放好，再通过setImageURI设置到ImageView，那么就像* iv4?.setImageBitmap(newBmp)，设置的newBmp是最终的绘图结果，saveLayer与restoreToCount操作的是在内存的newBmp，* 即便是ivx?.setImageURI后，newBmp内存数据变化，最终都是iv4里面的显示。为了细致观察这种区别，才先保存成不变的文件，再读文件加载出来观察。** 注意，因为restoreToCount了，图层叠加到原图上，所以显示的结果是最后面的叠加到最前面的，把最前面的遮住了。* 如果不restoreToCount，则不会叠加，因为saveLayer创建了一个透明图层，是在原图之上的绘制。*/iv4?.setImageBitmap(newBmp)}private fun saveBitmapToFile(bm: Bitmap): File? {var saveFile: File? = nullval savePath =Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES).toString()if (!Files.exists(Paths.get(savePath))) {Log.d("保存文件", "${savePath}不存在!")} else {saveFile = File(savePath, System.currentTimeMillis().toString() + ".jpeg")try {val saveImgOut = FileOutputStream(saveFile)//压缩bm.compress(Bitmap.CompressFormat.JPEG, 90, saveImgOut)saveImgOut.flush()saveImgOut.close()Log.d("保存文件", "Bitmap保存至 ${saveFile.absoluteFile.toPath()}")} catch (e: Exception) {e.printStackTrace()}}return saveFile}

如果把

canvas.restoreToCount()

全部注释掉，则为

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