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Flex 獲得png透明截圖的問題和解決方法

代碼大概這樣:

// displaObject 為需要截圖對像
var pngEncoder:PngEncoder = new PngEncoder();
var bitMapData:BitmpaData = new BitmpaData(displaObject.widht,displaObject.height);
bitMapData.draw(displaObject);
var imageByteArray:ByteArray = pngEncoder.encode(bitMapData);

但是得到結果並不透明,於是懷疑encode方法沒有包含Alpha通道。改為第二種方法:

var bytes:ByteArray = bitmapData.getPixels(new Rectangle(0,0,bitmapData.width,bitmapData.height));
var imageByteArray2:ByteArray = pngEncoder.encodeByteArray(bytes,bitmapData.width,bitmapData.height,true);

結果仍然沒有透明度信息!
於是仔細讀了手冊每一項找到如下一段話:
transparent:Boolean (default = true) — 指定位圖圖像是否支持每個像素具有不同的透明度。默認值為 true(透明)。若要創建完全透明的位圖,請將 transparent 參數的值設置為 true,將 fillColor 參數的值設置為 0x00000000(或設置為 0)。將 transparent 屬性設置為 false 可以略微提升呈現性能。
也就是說,transparent = true 還不行,fillColor還必須設置為 0x000000!!

var bitMapData:BitmpaData = new BitmpaData(displaObject.widht,displaObject.height,true,0x000000);

其實這樣設置挺說不通的,但是以後碰到問題還是要多看看手冊了!
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