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CC · Guest

Greetings -

I have a routine that is sending me a HBITMAP handle.

How can I use TBitmap (or something else if it would be better) to save the
bitmap to a file?

I've tried:

Graphics::TBitmap *tempBtMap = new Graphics::TBitmap();
tempBtMap->Handle=hbitmap;
tempBtMap->SaveToFile("c:\tmp\junk22.bmp");

---
But this gets me a blank file?

Any help would be much appreciated
Thanks,
CurtC

Damon Chandler (TeamB) · Guest

Hi Curt,
The code you posted should work if the HBITMAP is a handle to a DIB
section bitmap. If not--i.e., if the HBITMAP is a handle to a
device-dependent bitmap (DDB)--you might have to copy the palette
information as well (if the bitmap uses 8 or fewer bits per pixel). You
can test whether the bitmap is a DIB section bitmap or a DDB by using
the following code...

DIBSECTION bmp_info;
int const obj_size =
GetObject(hbitmap, sizeof(DIBSECTION), &bmp_info);
ShowMessage(obj_size);

If obj_size is 24, then it's a DDB; if obj_size is 84, then it's a DIB
section bitmap.

Also, you should ensure that the handle you're given is valid; test this
by dropping a TImage on your form and then doing...

Image1->Picture->Bitmap->Handle = hbitmap;
Image1->AutoSize = true;

Image1 should display the picture in its correct size. If all else
fails, try the SaveBitmap() function that's provided here...

http://tinyurl.com/4olyg

Good luck,
--
Damon (TeamB)
C++Builder Developer's Journal: http://bcbjournal.org
BCBCAQ: http://caq.bcbjournal.org

CC wrote:

CC · Guest

Damon -
I used the example code you supplied.
The obj_size returned zero (0).

I still cannot save the bitmap with:

Graphics::TBitmap *tempBtMap = new Graphics::TBitmap();
tempBtMap->Handle=hbitmap;
tempBtMap->SaveToFile("c:\tmp\junk.bmp");

(I get a zero length file)

But immediately after the code I can display it with the following.

LPBITMAPINFO bmi = (LPBITMAPINFO)::GlobalLock(hbitmap);
tempBtMap->Height = bmi->bmiHeader.biHeight;
tempBtMap->Width = bmi->bmiHeader.biWidth;
SetDIBits( tempBtMap->Canvas->Handle,
tempBtMap->Handle,
0,
(UINT) bmi->bmiHeader.biHeight,
lpBits, // calculated offset to bits
bmi, DIB_RGB_COLORS );

GlobalUnlock( hbitmap );
GlobalFree( hbitmap );

Form1->Image1->Picture->Assign(tempBtMap); //show it
delete tempBtMap;

------

One note about the the HBITMAP - it is a HBITMAP being returned from the
win32 twain manager.

I'm not sure why I can display it with the code, but cannot do anything
else, like saving it.

By the way - I bought your book on graphics - it is an awesome book, but it
is quite overwelming to me being a graphics newbie. Great job!

Thanks for the assistance,
Curt

----- Original Message -----
From: "Damon Chandler (TeamB)"
<editor (AT) REMOVE_THIS_SPAM_GUARD (DOT) bcbjournal.org>
Newsgroups: borland.public.cppbuilder.graphics
Sent: Tuesday, October 12, 2004 12:02 AM
Subject: Re: Use TBitmap to save HBITMAP to file

Damon Chandler (TeamB) · Guest

Curt,
If you can display the bitmap using SetDIBits(), then you actually
have a handle to a so-called DIB (device-independent bitmap). A DIB is
different from a DDB or a DIB section bitmap in that a DIB is not a true
GDI object; rather, it's a chunk of memory that contains a BITMAPINFO
structure and an array of pixels. A handle to a DIB (your hbitmap) is
nothing more than a handle to the memory chunk; this is why in your
displaying code you must first call the GlobalLock() function.

Here's a function to save a DIB to a file...

// saves a DIB to a file
DWORD SaveDIBToFile(
// name of the file to save as
IN LPCSTR filename,
// reference to the DIB
IN const BITMAPINFO& bmi,
// pointer to the pixels (if not packed)
IN const unsigned char* pBits
)
{
DWORD dwBytesWrote = 0;

// first determine the size (in bytes) of the color table
short num_colors = bmi.bmiHeader.biClrUsed;
if (num_colors == 0 && bmi.bmiHeader.biBitCount < Cool

{
num_colors = (1 << bmi.bmiHeader.biBitCount);
}
const size_t color_table_size =
sizeof(RGBQUAD) * num_colors;

// next, determine the size (in bytes) of the pixels array
const size_t pixels_size =
bmi.bmiHeader.biSizeImage != 0 ?
bmi.bmiHeader.biSizeImage :
abs(bmi.bmiHeader.biHeight) *
((((bmi.bmiHeader.biWidth *
bmi.bmiHeader.biBitCount) + 31) & ~31) >> 3);

// initialize the file header
BITMAPFILEHEADER bmfh;
bmfh.bfType = 0x4D42;
bmfh.bfSize =
// size of the file header
sizeof(BITMAPFILEHEADER) +
// size of the DIB's header
sizeof(BITMAPINFOHEADER) +
// size of the color table
color_table_size +
// size of the pixels array
pixels_size;
bmfh.bfOffBits = bmfh.bfSize - pixels_size;

// create the file
HANDLE hFile =
CreateFile(
filename, GENERIC_WRITE, 0, NULL,
CREATE_ALWAYS, FILE_ATTRIBUTE_NORMAL, NULL
);
if (hFile != INVALID_HANDLE_VALUE)
{
DWORD dwWritten = 0;

// write the file header
bool write_ok = WriteFile(
hFile, &bmfh, sizeof(BITMAPFILEHEADER),
&dwWritten, NULL
);
if (write_ok && (dwWritten == sizeof(BITMAPFILEHEADER)))
{
// accrue the number of bytes written
dwBytesWrote += dwWritten;

// write the DIB header
write_ok = WriteFile(
hFile, &bmi.bmiHeader, sizeof(BITMAPINFOHEADER),
&dwWritten, NULL
);
if (write_ok &&
(dwWritten == sizeof(BITMAPINFOHEADER)))
{
// accrue the number of bytes written
dwBytesWrote += dwWritten;

// write the color table
if (color_table_size != 0)
{
WriteFile(
hFile, bmi.bmiColors, color_table_size,
&dwWritten, NULL
);
// accrue the number of bytes written
dwBytesWrote += dwWritten;
}

// write the pixels
if (!pBits)
{
// assume a packed DIB if no
// pointer is supplied
pBits = reinterpret_cast<unsigned char*>(
const_cast<RGBQUAD*>(bmi.bmiColors) +
num_colors
);
}
WriteFile(
hFile, pBits, pixels_size, &dwWritten, NULL
);
// accrue the number of bytes written
dwBytesWrote += dwWritten;
}
}
CloseHandle(hFile);
}
return dwBytesWrote;
}

Based on the displaying code that you posted, I believe you'd call this
function as follows...

SaveDIBToFile("my_bitmap.bmp", *bmi, lpBits);

(You may need to cast the last variable to an unsigned char*.)

And, thanks, BTW, for the kind words about the book. This function is
actually from Chapter 7. Chapters 6 and 7 should get up to speed on
bitmaps.

Best of luck,
--
Damon (TeamB)
C++Builder Developer's Journal: http://bcbjournal.org
BCBCAQ: http://caq.bcbjournal.org

CC wrote:

CC · Guest

Damon-

Thank you very much - the code worked wonderfully.
Also - forgot to mention, your articles on bcbcaq were fabuluous they helped
me a great deal - now if I could just understand them to half the extent you
do.

Also - do you know of a decent portable way to convert bitmap files to tiff
files?
(I've looked at libtiff.org, but haven't found anything specific) I'm trying
to find a generic way to write tiff files in code that would be portable
between unix/PC.

I'm sure if I understood the graphics files I could write one, but it would
take me a long time to learn both formats, and translating between the 2.

Thanks again for your assistance, it is much appreciated - The TeamB/BCB
newsgroups is what brought me back to Borland C++ from the microsoft world

CurtC

"Damon Chandler (TeamB)" <editor (AT) REMOVE_THIS_SPAM_GUARD (DOT) bcbjournal.org>
wrote in message news:416c1107 (AT) newsgroups (DOT) borland.com...

Michel Leunen · Guest

CC wrote:

CC · Guest

Yep - I've heard about the GDI+ -
I'll have to see how to convert that -
One of the things I was shooting for was portability between windows and
unix - 1 common routine that would operate on both.

I'll definately look at the GDI+ option
Thank for the info.
Curt

----- Original Message -----
From: "Michel Leunen" <nospam (AT) noreply (DOT) please>
Newsgroups: borland.public.cppbuilder.graphics
Sent: Tuesday, October 12, 2004 2:29 PM
Subject: Re: Use TBitmap to save HBITMAP to file

Damon Chandler (TeamB) · Guest

Curt,