WndImage

Abstract

CWndImage implements the minimal steps required to display a bitmap. The class is "plug-and-play" for MFC, most of the magic happens in the OnPaint function which should be easy to port to Win32 or ATL. Some features like scaling, cutting and tiling were added on the way, when they were a spinoff of the required implementation (or existing snippets). 

Overview		Version 1.2
Sample application screenshot		Easy to use: add a CWndImage m_img member variable to your window class (dialog or whatever) for dialogs, place a static or a picture control on your dialog resource, and call m_img.CreateFromStatic. For other windows, simply call the m_img.Create use m_img.SetImg(IDB_BITMAPxxx) or m_img.SetImgFile("C:\\images\\cool.bmp")  anytime. Features: various stretch modes, tile, custom zoom align left/center/right, top/center/bottom window of source bitmap support for palettized display modes Download Source 12 K Source + Documentation Download Sample Project 122 K Sample Project, Documentation, Executable, Sample Images Download Version 1.1 70 K old version Sample Project + Documentation

Note on the demo: The flicker when resizing is caused by the dialog itself, not by the CWndImage. Avoiding this requires quite some work, so I didn't include it here.

Will not be done: image processing, rotating, shearing. Loading other file formats than BMP. For the latter you can use one of the many libraries to load images into an HBITMAP, and then continue. The class is neither optimized nor intended to handle large images. Using large images on weak hardware will hog the system.

Try it!

1. add the WndImage.h and wndImage.cpp to your project, #include wndimage.h where you need it
2. add a static or "picture" control to one of your dialogs. Give it an IDC_ST_IMG control ID.
3. Add a CWndImage m_img member variable to your dialog class
4. Add the following lines to OnInitDialog:
   m_img.CreateFromStatic( GetDlgItem(IDC_ST_IMG) );
   Hint: if you use a FormView, put this code into OnInitialUpdate. Thanks to V. Pontes for pointing out.
5. To select an image, and make it fit,add
   m_img.SetImg(IDB_MYBITMAP);  // specify a valid bitmap resource here
   m_img.SetBltMode(CWndImage::bltFitXY);
6. Enjoy

Documentation

Palette Issues (implemented in Version 1.2)

Correct display at 256 colors turned out to be more than a "quick fix". Well, I learnt a lot about bitmaps, palettes & GDI... Thanks to the codeproject & codeguru site. (I don't quite remember which actual article I used)

Load Bitmap:

For correct display on 256 color, the bitmap must be loaded as DIB section. This is the default (V1.2) for SetImg(resID), SetImg(resName), and SetImgFile.
Otherwise, Windows will map the bitmaps colors already when loading the bitmap, and this can look quite ugly. You can control this by the useDIB parameter in SetImg(File). In the sample, you can play around with the "use DIBSECTION" checkbox.

Capture Palette changes:

The image needs to redisplay after system palette changes. The corresponding message (WM_PALETTECHANGED) is only sent to top level windows, so here's what you have to do:

a) Add a WM_PALETTECHANGED handler to your top level window, and call the m_wndImg.OnAppPaletteChanged() function. This technique is used in the sample.

b) alternatively, you can place the following code in your handler:

// WM_PALETTECHANGED message handler (top level window)

void CMainFrame::OnPaletteChanged(CWnd* pFocusWnd ) 
{
  SendMessageToDescendants(WM_PALETTECHANGED, (WPARAM) pFocusWnd->GetSafeHwnd(), 0);
  CDialog::OnPaletteChanged(pFocusWnd);
}

This will forward the message to all child windows. CWndImage has a handler for this, and other windows should be unharmed.

The following sample images are included:

• 16M: True Color
• 256:  256 color, optimized palette including windows colors
• 16w: dithered to 16 windows standard colors
• 16:   dithered to optimized 16 color palette.

Revision History:

bitbucket c++ site © Peter Hauptmann. Questions & Comments to  cherea@cherea.de
page updated 29/02/04