Re: Convert PNG file to Bitmap without a DC?

From:

"Wil Stark" <wstark_NOSPAM_04@pobox.com>

Newsgroups:

microsoft.public.vc.mfc

Date:

Fri, 23 Jun 2006 13:30:37 -0700

Message-ID:

<1151094332.399950@newsreg.cos.agilent.com>

I think I've found an answer for my question here. Using ::GetDC(0) returns
the screen DC, and this DC can be used with CreateDIBitmap to create a
screen compatible HBITMAP.

"Wil Stark" <wstark_NOSPAM_04@pobox.com> wrote in message
news:1150995904.5833@newsreg.cos.agilent.com...

I'd like to store images resources as PNGs due to the compression over
bitmps. To load such a resource and get it converted to a bitmap for the
eventual Blit to my screen DC, I basically want the equivalent of
LoadBitmap. Better yet, I was thinking I would create a CBitmap derived
class "CPNGImage" that would have a "LoadPNGResource" method much like
CBitmap's LoadBitmap method. So far so good.

The stumbling block for me at this point is that the process of converting
the PNG to a bitmap seems to require a DC compatible with my device. This
is neatly encapsulated/shown in CxImage's MakeBitmap function:

HBITMAP CxImage::MakeBitmap(HDC hdc)
{
if ((!hdc) || (!hDib)) return NULL;
HBITMAP bmp = CreateDIBitmap(hdc, (LPBITMAPINFOHEADER)hDib, CBM_INIT,
GetBits(), (LPBITMAPINFO)hDib, DIB_RGB_COLORS);
return bmp;
}

Contrast this to LoadBitmap, which does not require an HDC, but will still
load a bitmap (16 or 24 bit color depth) from a resource and seems to
convert it to a 32bit color depth just like what BitBlt to my screen DC
wants. How does LoadBitmap do this without access to my screen DC? Or
rather, how can I accomplish this same thing for my PNG resource without a
screen DC? Or is this not possible?

I have a feeling the answer has something to do with DIB vs. DDB, etc.,
but I just can't seem to figure out what is going on here.

Thanks for any help you can offer.

- Wil