[Direct2D]不透明遮罩操作

Opacity Masks Overview(翻译随后就到)

http://msdn.microsoft.com/en-us/library/ee329947(v=VS.85).aspx

Use a Bitmap as an Opacity Mask with the FillOpacityMask Method

The FillOpacityMask method paints a rectangular region of a render target and then applies an opacity mask, defined by anID2D1Bitmap. Use this method when you have a bitmap that you want to use as an opacity mask for a rectangular region.

The following diagram shows an effect of applying the opacity mask (an ID2D1Bitmap with an image of a flower) to an ID2D1BitmapBrush with an image of a fern plant. The resulting image is a bitmap of a plant clipped to the flower shape.

 

Diagram of a flower bitmap used as an opacity mask on a picture of a fern plant

 

The following code examples shows how this is accomplished.

The first example loads the following bitmap, m_pBitmapMask, for use as a bitmap mask. The following illustration shows the output produced. Note that, although the opaque portion of the bitmap appears black, the color information in the bitmap has no effect on the opacity mask; only the opacity information of each pixel in the bitmap is used. The fully opaque pixels in this bitmap have been colored black for illustrative purposes only.