Re: From memDC to a Bitmap..... How?
David Webber schrieb:
"Jessica" <Jessica@discussions.microsoft.com> wrote in message
news:538ECBFE-DE0B-4E1B-9677-C42C1D5E0789@microsoft.com...
Hi All,
I am having a memDC (CDC*) in which I have drawn somethig, and Now I
want
to have a CBitmap object created from the memDC. Can anyone throw some
light
on how to do this?
CBitmap bmp;
bmp.CreateCompatibleBitmap(&cdc,rectBound.Width(), rectBound.Height());
This creates a CBitmap bmp, which has not yet been drawn, which is
compatible (in colour depth and so on) with CDC cdc.
Is this the correct way?
Not all of it.
And to get an HBITMAP from the CBitmap, can I directly cast it, because
there is an HBITMAP casting operator available for CBitmap ?
HBITMAP hbmp = (HBITMAP) bmp; // Is this ok?
Yes.
In more detail the steps to extract a bitmap from a DC are
You have a pointer to a DC whence you want to extract a bitmap, and you
know the size of the bitmap
CDC * pDC;
CSize size;
Then:
//-------------------------------------------
// Create a compatible "memory DC"
CDC memDC;
memDC.CreateCompatibleDC( pDC );
// Create a compatible bitmap
CBitmap Bmp;
Bmp.CreateCompatibleBitmap( pDC, size.cx, size.cy );
*******
An additional note to the reader:
Even if it looks tempting, it is important to NOT use memDC here.
Although memDC is compatible with pDC, the default bitmap that GDI selects into
any memory DC is a momochrome bitmap. The call
Bmp.CreateCompatibleBitmap( &memDC, size.cx, size.cy );
would create a momochrome bitmap because GDI creates a bitmap that is compatible
to the bitmap currently selected into the DC.
*******
// Select the new bitmap in the memory DC:
CBitmap *pOldBitmap = memDC.SelectObject( &Bmp );
// Copy the contents of pDC into memDC
memDC.BitBlt( 0, 0, size.cx, size.cy, pDC, 0, 0, SRCCOPY );
// Now Bmp has a copy of what was in pDC.
// Tidy the memDC:
memDC.SelectObject( pOldBitmap );
// Bmp is now safe from further drawing.
memDC.DeleteDC();
// We have now finished and Bmp
// is our bitmap.
//-------------------------------------------
I have always found this a bit of a faff, but that's the way DCs are
designed to work and one gets used to it.
The above is the simplest usage (and it was from memory so sorry if
there are errors) - check the APIs involved for different bells and
whistles!
Dave