actionscript-3 – DisplacementMapFilter如何工作？

问题是我的目标图像包含不在源图像中的像素！

例如,我使用此BitMapData获取UNICOLOR 10 * 10像素的“源图像”：

sourceBitmap = new BitmapData(BITMAP_WIDTH,BITMAP_HEIGHT,false,0x000002);

produce:

  0   1   2   3   4   5   6   7   8   9
[002,002,002] Row 0
[002,002] Row 1
[002,002] Row 2
[002,002] Row 3
[002,002] Row 4
[002,002] Row 5
[002,002] Row 6
[002,002] Row 7
[002,002] Row 8
[002,002] Row 9

现在,我采用这个BLACK位移MAP并添加一个蓝色方块：

displacementBitmap = new BitmapData(BITMAP_WIDTH,0x000000);
for(i=5;i<10;i++)
    for(j=5;j<10;j++)
        displacementBitmap.setPixel(i,j,255);

produce:

 0   1   2   3   4   5   6   7   8   9 
[000,000,000] Row 0
[000,000] Row 1
[000,000] Row 2
[000,000] Row 3
[000,000] Row 4
[000,255,255] Row 5
[000,255] Row 6
[000,255] Row 7
[000,255] Row 8
[000,255] Row 9

结果：

displacementFilter = new DisplacementMapFilter();
displacementFilter.alpha=0;
displacementFilter.color=0;
displacementFilter.mapPoint=new Point(0,0);
displacementFilter.scaleX=1;
displacementFilter.scaleY=1;
displacementFilter.componentX = flash.display.BitmapDataChannel.BLUE;
displacementFilter.componentY = flash.display.BitmapDataChannel.BLUE;
displacementFilter.mapBitmap = displacementBitmap;

destinationBitmap = new BitmapData(BITMAP_WIDTH,0xFFFFFFFF);
destinationBitmap.applyFilter(
    sourceBitmap.bitmapData,new Rectangle(0,BITMAP_WIDTH,BITMAP_HEIGHT),new Point(0,0),displacementFilter
);

produce:        

  0   1   2   3   4   5   6   7   8   9 
[002,001,001] Row 5
[002,001] Row 6
[002,001] Row 7
[002,001] Row 8
[002,001] Row 9

所以我不明白为什么我的’001’像素在源图像中不存在.

非常感谢你.