[perl-win32-gui-users] Window alpha/colorkey

[Luigino M. <lma...@ou...>]

Hi,
    I searched in this mailing list how to create a semi-transparent =
looking window and a free-shaped one (see Win32 SDK - Layered Windows =
http://msdn.microsoft.com/library/default.asp?url=3D/library/en-us/dnwui/=
html/layerwin.asp) and found nothing about it, so i searched on MSDN and =
found the API code and tried until i got it.

Note that this functionality is fully supported by Windows 2000/XP only.

Here is the code, hope it will be useful to someone else...

#-------------------------------------------------------------
# use Win32::GUI etc...=20

use Win32;
use Win32::API;

use constant GWL_EXSTYLE             =3D> -20;
use constant WS_EX_LAYERED           =3D> 0x00080000;
use constant LWA_COLORKEY            =3D> 0x00000001;
use constant LWA_ALPHA               =3D> 0x00000002;

# BOOL SetLayeredWindowAttributes(
# HWND hwnd,           // handle to the layered window
# COLORREF crKey,      // specifies the color key
# BYTE bAlpha,         // value for the blend function
# DWORD dwFlags        // action
# );
my $SetLayeredWindowAttributes =3D new Win32::API("user32", =
"SetLayeredWindowAttributes", [ 'N', 'N', 'I', 'N' ], 'N') or die =
"Cannot create SetLayeredWindowAttributes()";

# ... here create your window object ($winObj) as usual...

# set alpha channel value aka opaqueness for your window, range 0-255 =
(transparent-opaque)
my $alpha =3D 200;

# set color key value for your window, format is 0x00rrggbb, range =
0x00000000-0x00ffffff
# window regions painted with $colKey color will be completely =
trasparent (to mouse events too..)
my $colKey =3D 0x0000FF00;

# set the flags needed for alpha, colorkey or both...
# LWA_ALPHA activates alpha opaqueness using $alpha value
# LWA_COLORKEY activates color key using $colKey value
my $flags =3D LWA_ALPHA | LWA_COLORKEY;

# add the WS_EX_LAYERED extended style to your window (needed to use =
alpha/colorkey properties)
$objWin->SetWindowLong(GWL_EXSTYLE, Win32::GUI::GetWindowLong($objWin, =
GWL_EXSTYLE) | WS_EX_LAYERED );

# uncomment this and your window wil be COMPLETELY transparent to mouse =
events...
#$objWin->SetWindowLong(GWL_EXSTYLE, Win32::GUI::GetWindowLong($objWin, =
GWL_EXSTYLE) | WS_EX_TRANSPARENT );

# activate alpha/colorkey
$SetLayeredWindowAttributes->Call($objWin->{-handle}, $colKey, $alpha, =
$flags) or die "\n".Win32::GetLastError();

# ... now $objWin->Show() your window as usual...
#-----------------------------------------------------

Bye.

    Luigino Masarati
    OutSys snc.