[Lazarus] Converting Icon from Windows handle to TBitmap with transparency

[Maxim Ganetsky]

15.07.2011 2:10, cobines пишет:
> 2011/6/8 cobines<cobines at gmail.com>:
>> Hello everyone.
>>
>> I want to convert an icon retrieved by Windows API to a TBitmap saving
>> transparency. As I understand transparency can be achieved by:
>> - using an additional Mask bitmap
>> - using 32bpp TBitmap with alpha channel
>>
>> Having the handle to an icon from WINAPI, I convert it to TBitmap the
>> following way:
>>
>> function IconToBitmap(h: HICON): TBitmap;
>> var
>>   icon: TIcon;
>> begin
>>   icon := TIcon.Create;
>>   icon.Handle := h;
>>   Result := TBitmap.Create;
>>   Result.Assign(icon);
>>   icon.Free;
>> end;
>>
>> But this does not preserve transparency. I have to add:
>>
>> Result.Mask(Result.TransparentColor);
>>
>> Is this the correct way?
>>
>> Why Icon does not automatically have a Mask? It does have
>> TransparentMode and TransparentColor correctly assigned.
>> TransparentColor is copied to TBitmap but the Mask is not copied or
>> not automatically created.
>
> I finally had time to do some digging.
>
> Turns out Mask bitmap exists in both TIcon and TBitmap (mask image is
> copied). Problem is Masked is False in TBitmap. This is because in
>
> procedure TRasterImage.Assign(Source: TPersistent);
>
> there is line
>
>      FMasked := SrcImage.FMasked;
>
> which is wrong. It should be :
>
>      FMasked := SrcImage.Masked;
>
> FMasked is never set to True for TCustomIcon. Instead Masked property
> is overridden to always return True. Therefore after
> TBitmap.Assign(TIcon) FMasked is False, while it should be True.

Please create a bug report.

> Also a question:
> Why TIcon always has Masked=True?
>
> Icons with alpha channel don't work properly with TIcon and they don't
> use Mask. Is support for alpha channel icons simply not implemented?

-- 
Best regards,
  Maxim Ganetsky                  mailto:ganmax at narod.ru