Android Canvas画布saveLayer与对应restoreToCount，Kotlin-蒲公英云

Android Canvas画布saveLayer与对应restoreToCount，Kotlin

亦凉 2024-02-05 17:36 109阅读 0赞

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Canvas
        canvas.drawBitmap(originBmp, 0f, 0f, null)
        iv?.setImageURI(Uri.fromFile(saveBitmapToFile(newBmp)))
        val paint = Paint(Paint.ANTI_ALIAS_FLAG)
        paint.color = Color.RED
        paint.textSize = 40f
        paint.style = Paint.Style.STROKE
        paint.strokeWidth = 2f
        paint.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fly
        val layer3 = canvas.saveLayer(0f, 0f, canvas.width.toFloat(), (canvas.height.toFloat() * 0.5).toFloat(), null)
        canvas.drawColor(Color.BLUE)
        val x = 50f
        val y = 150f
        canvas.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? = null
        val 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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