Author: Jonas Bilinkevicius

I am trying to do regioning backwards. I am writing an application that will read 
in a bitmap, allow the user to set a transparent colour, and then calculate the 
point set that would be needed to make that region transparent. I then want to 
supply the user with the coordinates as a set of coordinates, i.e. I want to 
extract it from a region format. Why? Because that's how Winamp takes the data in 
to make its custom shaped forms. But I can't seem to figure out how to pull the 
data out.

Answer:

One thing I found is that you must create a region prior to GetWindowRgn. I thought 
that one was created by default. I made a function that does what you need:

1   procedure TForm1.ShowRgnInfo(Rgn: HRGN);
2   type
3     RgnRects = array[0..1000] of TRect;
4     PRgnRect = ^RgnRects;
5   var
6     RgnData: PRgnData;
7     Size: DWORD;
8     i: Integer;
9     R: TRect;
10    RgnPtr: PRgnRect;
11  begin
12    Size := GetRegionData(Rgn, 0, nil);
13    Memo1.Lines.Add('Size = ' + IntToStr(Size));
14    GetMem(RgnData, Size);
15    GetRegionData(Rgn, Size, RgnData);
16    Memo1.Lines.Add('Number of Rectangles = ' + IntToStr(RgnData.rdh.nCount));
17    RgnPtr := @RgnData.Buffer;
18    for i := 0 to RgnData.rdh.nCount - 1 do
19    begin
20      R := RgnPtr[i];
21      Memo1.Lines.Add('Rect ' + IntToStr(i));
22      Memo1.Lines.Add(IntToStr(R.Left) + ', ' + IntToStr(R.Top) + ', ' +
23        IntToStr(R.Right) + ', ' + IntToStr(R.Bottom));
24    end;
25  end;