A tool to convert bitmaps to region files

Environment: VC++ 4.2

Since the arcticle
Transparent Window
by Franz Polzer helped
me a lot, I would like to contribute a little tool that converts bitmaps
to region-files suitable to use as a window-mask (SetWindowRgn).

Why does anybody need this tool?

  • its flexible; its possible to adjust the key-color
  • its fast (not the tool, but your app); loading a region is better than
    creating it online

  • its free; source is included

How to use it?

    enter a source bitmap path (or press browse)

  • enter a key color (or click onto any pixel of the source bitmap)
  • press “calc !” wait and see the result
  • enter a destination path (or press browse)
  • press “write”

To use those region-files in your own project, you need to do the following:
Import the *.RGN-file into your project-resources. The type of that resource
needs to be set to “Data”.

You can also import it manually by editing your *.rc file.
Just insert something like the following:


Below is some example code that loads and activates a region,
it should be called from something like “OnInitDialog”.

//nRegionID – resource ID of the region data
BOOL CTransparentWnd::InitRegion (unsigned short nRegionID)
const char *MSGCAPTION=”Init Region”;
HRSRC hrsrc; //handle of the resource
HGLOBAL hmem; //handle to resource memory
DWORD dwSize; //size of our resource
RGNDATA *rd; //region data
CRgn rgn; //the region itself

//try to locate the resource
if ((hrsrc=FindResource(NULL,
MessageBox (“failed to find region”,MSGCAPTION,MB_OK);
return FALSE;
//load the resource
if ((hmem=LoadResource (NULL,hrsrc)) == NULL)
MessageBox (“failed to load region”,MSGCAPTION,MB_OK);
return FALSE;
//get the size of the region-data structure (= header + data)
if ((dwSize=SizeofResource (NULL,hrsrc)) == 0)
MessageBox (“region has an invalid size”,MSGCAPTION,MB_OK);
return FALSE;
//lock the resource to get a pointer for it
if ((rd=(RGNDATA *)LockResource (hmem)) == NULL)
MessageBox (“failed to lock resource memory”,MSGCAPTION,MB_OK);
return FALSE;
//create a region from our data
if (!rgn.CreateFromData (NULL,dwSize,rd))
MessageBox (“failed to create a region from that data”,MSGCAPTION,MB_OK);
return FALSE;
if (!SetWindowRgn (GetSafeHwnd(),(HRGN)rgn,TRUE))
MessageBox (“failed to set the region for that window”,MSGCAPTION,MB_OK);
return FALSE;
//NOTE: win32-based apps do not need to unlock or free loaded resources (not manually)
return TRUE;

Download project files – 34 KB

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