SetLayeredWindowAttributes function Advanced GDI routines

Unit

acGraphics

Declaration

function SetLayeredWindowAttributes(

hWnd: hWnd;       // handle to the layered window

crKey: COLORREF;  // specifies the color key

bAlpha: Byte;     // value for blend function

dwFlags: LongInt  // action

): LongInt;

Description

The SetLayeredWindowAttributes function sets the opacity and transparency color key of a layered window.

Parameters
hwnd

[in] 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.

crKey

[in] 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 convert TColor value to the COLORREF, use ColorToRGB function.

bAlpha

[in] 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

[in] Specifies an action to take. This parameter can be one or more of the following values.

Value

Meaning

LWA_COLORKEY

Use crKey as the transparency color.

LWA_ALPHA

Use bAlpha to determine the opacity of the layered window.

Return Values

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.

Requirements

Windows NT/2000: Requires Windows 2000 or later.

Windows 95/98: Unsupported.

If you call this function on Win95, or on Win98 with AW_BLEND parameter — nothing happends.

See also

acWin2kEffects component.

acMakeTranslucentWindow and acMakeOpaqueWindow procedures.