SetLayeredWindowAttributes function

Sets the opacity and transparency color key of a layered window.

Syntax

BOOL SetLayeredWindowAttributes(
  HWND     hwnd,
  COLORREF crKey,
  BYTE     bAlpha,
  DWORD    dwFlags
);

Parameters

hwnd

Type: HWND

A handle to the layered window. A layered window is created by specifying WS_EX_LAYERED when creating the window with the CreateWindowEx function or by setting WS_EX_LAYERED via SetWindowLong after the window has been created.

Windows 8:  The WS_EX_LAYERED style is supported for top-level windows and child windows. Previous Windows versions support WS_EX_LAYERED only for top-level windows.

crKey

Type: COLORREF

A COLORREF structure 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.

bAlpha

Type: BYTE

Alpha value used to describe the opacity of the layered window. Similar to the SourceConstantAlpha member of the BLENDFUNCTION structure. When bAlpha is 0, the window is completely transparent. When bAlpha is 255, the window is opaque.

dwFlags

Type: DWORD

An action to be taken. This parameter can be one or more of the following values.

Value Meaning
LWA_ALPHA
0x00000002
Use bAlpha to determine the opacity of the layered window.
LWA_COLORKEY
0x00000001
Use crKey as the transparency color.

Return Value

Type: Type: BOOL

If the function succeeds, the return value is nonzero.

If the function fails, the return value is zero. To get extended error information, call GetLastError.

Remarks

Note that once SetLayeredWindowAttributes has been called for a layered window, subsequent UpdateLayeredWindow calls will fail until the layering style bit is cleared and set again.

For more information, see Using Layered Windows.

Requirements

   
Minimum supported client Windows 2000 Professional [desktop apps only]
Minimum supported server Windows 2000 Server [desktop apps only]
Target Platform Windows
Header winuser.h (include Windows.h)
Library User32.lib
DLL User32.dll

See Also

AlphaBlend

COLORREF

Conceptual

CreateWindowEx

Other Resources

RGB

Reference

SetWindowLong

TransparentBlt

UpdateLayeredWindow

Using Windows

Windows