Pointer to a COLORREF value that specifies the transparency color key to be used when composing the layered window. All pixels painted by the window in this color will be transparent. To generate a COLORREF, use the RGB macro.
Alpha value used to describe the opacity of the layered window. For more information, see the SourceConstantAlpha member of the BLENDFUNCTION structure. When bAlpha is 0, the window is completely transparent. When bAlpha is 255, the window is opaque.
Specifies an action to take. This parameter can be one or more of the following values. For a list of possible values, seeSetLayeredWindowAttributes.