Preface
The sample demo workspace includes two projects: DIBSectionTest for Win32
environments, and DIBSectionTestCE for CE environments that demonstrate the DIBSection
wrapper. You will need the CE SDKs from Microsoft to be installed before you can build DIBSectionTestCE.dsw.
There is also a version of the DIBSection wrapper ported by Kenny Goers with no dependancies on MFC. This version is currently slightly out of sync with the MFC version, and is provided as a convenience only.
Introduction
Device Independant Bitmaps (DIBs) offer a means to manipulate and display
bitmaps in a form that is independant of the current display setting of your
computer. They are also the format of the standard windows .BMP file, and so
having a means to load, display and modify DIBs is very handy.
Win32 offers many different ways of dealing with DIBs, including the standard
DIB functions such as SetDIBitsToDevice
, GetDIBits
etc,
the DrawDib
functions, and the GDI functions such as BitBlt
for use with DIBsections.
However, when working in a CE environment, many of the usual functions we
know and love have been discarded in an effort to reduce the size of the overall
OS, and as such we are only left with the possibility of using DDB's (via CBitmap
)
or DIBSections. This is not too much of a handycap though since DIBSections are,
in a way, superior to plain DIBs in that they have an associated HBITMAP
handle,
and hence can be manipulated via the GDI functions such as BitBlt
and StretchBlt
.
Furthermore, the handle to a DIBSection can be selected into a memory DC and then
drawn to directly using the TextOut
, Line
etc GDI functions.
This is far easier than accessing the bits of a DIB yourself and plotting the pixels
one by one.
The only problem with DIBsections, from an MFC programmers point of view, is
that there is no DIBSection wrapper. Jeff Prosise, in his book Programming Windows
95 with MFC discusses DIBSections and how great they are, but states that because
the next version of MFC will have a DIBSection wrapper class, there is no
point in him supplying one in his book. Oops! Several updates to MFC have come and gone
since that book was written and still there is no sign of a DIBSection wrapper
class.
With the advent of CE, DIBSections have become even more important. Here I
present the CDIBSectionLite
class - a DIBSection wrapper class for Win32
and WinCE platforms. This class provides a simple interface to DIBSections including
loading, saving and displaying DIBSections. Full palette support is provided for Win32
and CE 2.11 and above.
Note that CE introduces a new bitmap depth, namely 2 bits per pixel. This is for
older 4-level grey scale devices. CDIBSectionLite
supports this pixel
depth in CE builds only.
Creating and displaying DIBSections
The first step in creating a DIBSection is to fill out a BITMAPINFOHEADER
structure. If you are creating a DIBSection from scratch then just fill in
these values with whatever you like. If, on the other hand, you wish to
convert a DDB to a DIBSection then your best friend is the GetDIBits function.
It fills in the BITMAPINFOHEADER
structure for you by querying the values of
the supplied bitmap.
Unfortunately CE does not support this function and so you must do this yourself.
While this is no great drama it does make it a little more difficult to get the
colour table info from the supplied bitmap. Microsoft have kindly helped us programmers
along by writing the KB article HOWTO: Get the Color Table of a DIBSection in Windows
CE. One limitation of the code in the KB article is that it only extracts color
table info for bitmaps that are DIBSections themselves. CDIBSectionLite
gets around this by synthesizing a half-tone color table for DDB's without color
table info.
Once you have the BITMAPINFOHEADER
structure, including the color table entries
filled in, simply call CreateDIBSection
. This funtion will return a HBITMAP
handle plus a pointer to the actual image bits. What more could you ask for!
To actually display the DIBSections you simply use the tried and true windows
GDI functions (BitBlt etc). Some functionality is lost in CE, such as GDIFlush
and SetStretchBltMode, but on the whole a HBITMAP created as a DIBSection is no
different to use than a HBITMAP from a DDB.
The CDIBSectionLite
class includes support for the DrawDib functions. These provide
high speed display as well as dithering, but unfortunately are not available on CE.
To toggle between using the windows GDI and the DrawDib routines, use the
CDIBSectionLite::SetDither(...)
function.
Using CDIBSectionLite
This class is very simple to use and wraps all the messy plumbing from view.
The bitmap can be set using either SetBitmap()
(which accepts either a Device
dependant or device independant bitmap, or a resource ID) or by using Load()
,
which allows an image to be loaded from disk. To display the bitmap simply use
Draw or Stretch.
eg.
CDIBsectionLite dibsection;
dibsection.Load(_T("image.bmp"));
dibsection.Draw(pDC, CPoint(0,0));
CDIBsectionLite dibsection;
dibsection.SetBitmap(IDB_BITMAP);
dibsection.Draw(pDC, CPoint(0,0));
CDIBsectionLite API
The CDIBSectionLite
API includes methods for loading and
displaying images, methods to extract information about the image, as well as
palette options for getting and setting the current palette. Note that the
palette methods are only available in Win32 or in CE 2.11 or later.
HBITMAP GetSafeHandle() const
operator HBITMAP() const
CSize GetSize() const
int GetHeight() const
int GetWidth() const
int GetPlanes() const
int GetBitCount() const
LPVOID GetDIBits()
LPBITMAPINFO GetBitmapInfo()
DWORD GetImageSize() const
LPBITMAPINFOHEADER GetBitmapInfoHeader()
LPRGBQUAD GetColorTable()
LPRGBQUAD GetColorTable()
BOOL SetColorTable(UINT nNumColors, RGBQUAD *pColors);
int GetColorTableSize()
CPalette *GetPalette();
BOOL SetPalette(CPalette* pPalette);
BOOL SetLogPalette(LOGPALETTE* pLogPalette);
BOOL SetBitmap(UINT nIDResource);
BOOL SetBitmap(LPCTSTR lpszResourceName);
BOOL SetBitmap(HBITMAP hBitmap, CPalette* pPalette = NULL);
BOOL SetBitmap(LPBITMAPINFO lpBitmapInfo, LPVOID lpBits);
BOOL Load(LPCTSTR lpszFileName);
BOOL Save(LPCTSTR lpszFileName);
BOOL Copy(CDIBSectionLite& Bitmap);
BOOL Draw(CDC* pDC, CPoint ptDest, BOOL bForceBackground = FALSE);
BOOL Stretch(CDC* pDC, CPoint ptDest, CSize size, BOOL bForceBackground = FALSE);
BOOL SetDither(BOOL bDither);
BOOL GetDither();
void DeleteObject()
Latest Updates
- 4 May 2000 - The class was updated with corrections from Jim Miller
of 3DFX to correct a bug with compressed bitmaps.
- 20 Sep 2000 - Fixed Bug fix in Save() (saving 4 bytes too many - Tadeusz Dracz)
Allowed lpBits to be NULL in SetBitmap - Don Grasberger
Fixed NumColorEntries bug - Itay Szekely
Fixed buffer overrun bug in Load() - Itay Szekely
- 5 Apr 2001 - Fix for 16/32 bpp bitmaps for PocketPC's (Dan Robbins)
Non-MFC port (Kenny Goers)
- 22 May 2001 - Fix for missing break in 24bpp case of NumColorEntries (Steve Kramp)