Android Canvas画布saveLayer与对应restoreToCount，Kotlin

亦凉 2024-02-05 17:36 70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
        }

![71d48cb2403e4c3b84dd093fedca0d22.png][]

如果把

canvas.restoreToCount()

全部注释掉，则为

![83132b1386dc48c3ba0593f4bc0d4965.png][]

[Android Canvas状态save与restore，Kotlin-CSDN博客文章浏览阅读218次，点赞3次，收藏3次。文章浏览阅读9.6k次。文章浏览阅读1.8k次。/\*Java代码 将Drawable转化为Bitmap \*/ Bitmap drawableToBitmap(Drawable drawable) \{ int width = drawable.getIntrinsicWidth();Android Material Design ：LinearLayoutCompat添加分割线divider\_linearlayout 分割线-CSDN博客。![favicon32.ico][]https://blog.csdn.net/zhangphil/article/details/135113616][Android Canvas_save_restore_Kotlin-CSDN_218_3_3_9.6k_1.8k_Java_ _Drawable_Bitmap _ Bitmap drawableToBitmap_Drawable drawable_ _ int width _ drawable.getIntrinsicWidth_Android Material Design _LinearLayoutCompat_divider_linearlayout _-CSDN_favicon32.ico_https_blog.csdn.net_zhangphil_article_details_135113616]

[71d48cb2403e4c3b84dd093fedca0d22.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/30/6ef3ad4f2a0848aa8429cb612fbc4a37.png
[83132b1386dc48c3ba0593f4bc0d4965.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/30/976a45bcd82242a0aa747404bf1b8e09.png
[favicon32.ico]: https://image.dandelioncloud.cn/pgy_files/images/2024/01/30/e07123cd391441ccbae50f8c27d314b5.png
[Android Canvas_save_restore_Kotlin-CSDN_218_3_3_9.6k_1.8k_Java_ _Drawable_Bitmap _ Bitmap drawableToBitmap_Drawable drawable_ _ int width _ drawable.getIntrinsicWidth_Android Material Design _LinearLayoutCompat_divider_linearlayout _-CSDN_favicon32.ico_https_blog.csdn.net_zhangphil_article_details_135113616]: https://blog.csdn.net/zhangphil/article/details/135113616