RE: [GD-Windows] In memory bitmap to HBITMAP

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To avoid confusion, I should also mention that Jon Watte's example works
regardless of what is in the memory DC because he is using CreateDIBSection,
not CreateDIBitmap.

CreateDIBSection = device independent bitmap
CreateDIBitmap = device dependent bitmap. (Why it's not CreateDDBitmap or
something sensible I don't know).

Device dependent bitmaps give better GDI performance because they are in
some device-friendly format.

Andrew Grant
Hothouse Creations 

> -----Original Message-----
> From: Andrew Grant [mailto:And...@ho...]
> Sent: 07 December 2001 10:41
> To: gam...@li...
> Subject: RE: [GD-Windows] In memory bitmap to HBITMAP
> 
> 
> Ahh, remembered what the problem was :)
> 
> CreateCompatibleDC creates a memory DC. By default memory 
> DC's have a 1x1
> monochrome surface so when you call CreateDIBitmap you are 
> creating a bitmap
> which is the same type as that DC, e.g monochrome. Try 
> passing in the DC of
> your window instead to CreateDIBitmap. 
> 
> 
> To explain further; (stuff you may/may not know)
> 
> In Windows DCs are your interface for drawing to the object 
> they contain.
> Screens, Bitmaps and so on. When you call CreateCompatibleDC you are
> returned a compatible but empty DC (well, 1x1 b/w) that you 
> can then use to
> draw to. Compatible doesn't mean format-wise (after all you can BitBlt
> between DCs of different colour depths), it means compatible 
> in some device
> way, in this case compatible with the screen. However until you place
> something into that DC then you are using the default 1x1 monochrome
> surface.
> 
> For instance if you wanted to draw text to a HBITMAP using 
> GDI you put that
> hbmp into the DC first so you are using that. Something like...
> 
> // create a dc
> HDC hdc = CreateCompatibleDC();
> 
> // select the bitmap into the dc
> HGDIOBJ hOld = SelectObject(hdc, hbmp);
> 
> // draw your text
> DrawText(hdc, "blah blah", ...);
> 
> // remove the hbmp from the dc
> SelectObject(hdc, hOld);
> 
> // delete the dc
> DeleteDC(hdc);
> 
> 
> 
> Another example. To solve your problem you could do
> 
> HDC hdc = CreateCompatibleDC();			// 
> create a memory DC
> 
> HBITMAP = CreateBitmapIndirect();			// 
> creates an empty
> bitmap of the specified dimensions and depth
> 
> // select the new bmp into the DC
> HGDIOBJ hOld = SelectObject(hdc, hbmp);
> 
> CreateDIBitmap(hdc, ...);
> 
> Now at this point you have loaded your new bitmap with the 
> same color depth
> as the bitmap you created with CreateBitmapIndirect(), 
> because that was
> format of the bitmap in the DC you used with CreateDIBitmap, 
> not the default
> 1x1 monochrome one. Of course this isn't always good method 
> because you are
> allocating extra resources with CreateBitmapIndirect, however 
> this technique
> is useful for the case where the users desktop is running in 
> 16-bit color
> and you want to work with 24-bit images.
> 
> It's good to think of a DC as an interface you use to draw on 
> something. In
> the case of WM_PAINT that 'something' is the screen, in the 
> case of memory
> DCs it is the bitmap you place in them with SelectObject. 
> 
> 
> Hope this helps somewhat.
> 
> 
> Andrew Grant
> Hothouse Creations 
> 
> 
> 
> > -----Original Message-----
> > From: Andrew Grant [mailto:And...@ho...]
> > Sent: 07 December 2001 09:57
> > To: gam...@li...
> > Subject: RE: [GD-Windows] In memory bitmap to HBITMAP
> > 
> > 
> > I've had this before, I can't remember what caused it but it 
> > turned out to
> > be a "duh" error on my part. Code Guru (www.codeguru) is a 
> > great site for
> > all sorts of GDI programming trickery. It's MFC based but the 
> > techniques are
> > sound and it's not a great deal of pain to implment any of 
> > the samples in
> > Win32. In this case 
> > http://www.codeguru.com/bitmap/bitmap_from_bmp.shtml. 
> > 
> > On another note, have you thought about using LoadImage() 
> > instead rather
> > than doing it manually?
> > 
> > Andrew Grant
> > Hothouse Creations 
> > 
> > 
> > 
> > > -----Original Message-----
> > > From: Brian Hook [mailto:bri...@py...]
> > > Sent: 07 December 2001 02:04
> > > To: gam...@li...
> > > Subject: [GD-Windows] In memory bitmap to HBITMAP
> > > 
> > > 
> > > I'm struggling with something fairly basic -- I want to 
> > load a BMP out
> > > of a compressed file, convert to an HBITMAP, then blit it 
> > into a DDraw
> > > surface.  I know how to do the first and last part, but the 
> > middle is
> > > causing problems.  Even worse, I'm not getting any errors.
> > > 
> > > Loading the bitmap doesn't seem to be a problem.  I load it 
> > > up and parse
> > > and find the BITMAPFILEHEADER and BITMAPINFOHEADER no 
> probs.  I also
> > > locate the raw bits no problem (and inspect with the 
> > debugger to make
> > > sure I'm getting what I think I'm getting -- in this case, solid
> > > magenta).  Looks fine.
> > > 
> > > The next step is to create a DC compatible with the desktop:
> > > 
> > > HDC hDC = CreateCompatibleDC( NULL );
> > > 
> > > I then create a HBITMAP compatible with DC, and using the 
> > > bits I pulled:
> > > 
> > > HBITMAP hbm;
> > > 
> > > hbm = CreateDIBitmap( hDC, lpBMIH, CBM_INIT, lpBits, lpBMIH,
> > > DIB_RGB_COLORS );
> > > 
> > > lpBMIH are simply pointers to the appropriate 
> > BITMAPINFOHEADER.  They
> > > have correct values in them.  The bitmap is returned successfully.
> > > 
> > > To verify things, I grab the bits out of the Bitmap to make sure
> > > everything is cool:
> > > 
> > > GetDIBits( hDC, hbm, 0, iHeight, tempbuffer, &bmi, 
> DIB_RGB_COLORS );
> > > 
> > > It returns the correct number of scan lines, but tempbuffer 
> > is filled
> > > with black.  This means either the CreateDIBitmap() filled in 
> > > the bitmap
> > > with black, or the GetDIBits() failed somehow.  I can't 
> > > figure out which
> > > is the real culprit, but the bitmap is pretty much a black square.
> > > 
> > > Any suggestions on how to hunt this down?
> > > 
> > > 
> > > 
> > 
> > 
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> 
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