Re: [perl-win32-gui-users] AlphaCopy NOT to DC?

[Sean H. <jal...@ho...>]

On Thu, 25 Jan 2007 09:44:59 -0700, alexander Serechenko Alexander  =

<sk...@gm...> wrote:

> Is there any way to copy some transparent image over another?
> Only way I found is to use AlphaCopyToDC to some virtual DC, but i
> can't find any way to get Win32::GUI::DC not associated with any
> device.
> Is any one can help me?

Win32::GUI::DC::CreateCompatibleDC()

Creates a memory device context (DC) compatible with the specified devic=
e.

That's all the documentation there is. According to the source (DC.xs), =
it  =

returns a Win32::GUI::DC object, not just a handle. Of course, if it is =
 =

just a handle, it's easy enough to do:

my $dc =3D bless {
	-handle =3D> Win32::GUI::CreateCompatibleDC(),
}, 'Win32::GUI::DC';

And according to Microsoft, calling it with no handle should give you a =
DC  =

compatible with the current screen. Here's an excerpt:

The CreateCompatibleDC function creates a memory device context (DC)  =

compatible with the specified device.

HDC CreateCompatibleDC(
   HDC hdc   // handle to DC
);

Parameters
hdc
[in] Handle to an existing DC. If this handle is NULL, the function  =

creates a memory DC compatible with the application's current screen.

Return Values

If the function succeeds, the return value is the handle to a memory DC.=


If the function fails, the return value is NULL.

Remarks

A memory DC exists only in memory. When the memory DC is created, its  =

display surface is exactly one monochrome pixel wide and one monochrome =
 =

pixel high. Before an application can use a memory DC for drawing  =

operations, it must select a bitmap of the correct width and height into=
  =

the DC. To select a bitmap into a DC, use the CreateCompatibleBitmap  =

function, specifying the height, width, and color organization required.=


When a memory DC is created, all attributes are set to normal default  =

values. The memory DC can be used as a normal DC. You can set the  =

attributes; obtain the current settings of its attributes; and select  =

pens, brushes, and regions.