Error in CreatePolygonRgn

[edgarrod71]

there is a bug in the GetMem of the Gtk2Winapi, it simply does not allocate memory when I try to create a Polygonal Region... here's the code, maybe I'm doing something wrong?

var Pol: PPoint;
ButtonRgn: THandle;

...
begin
  Pol[0].X := X-100; Pol[0].Y := Y-100;
  Pol[1].X := X-100; Pol[1].Y := Y+100;
  Pol[2].X := X+100; Pol[2].Y := Y+100;
  Pol[3].X := X+100; Pol[3].Y := Y-100;
  Pol[4].X := X; Pol[4].Y := Y-100;
  Pol[5].X := X-100; Pol[5].Y := Y-100;

  ButtonRgn := CreatePolygonRgn(Pol, 6, WINDING);
...
end;

[Thaddy]

You are just using a pointer, but the structure at the pointer is nowhere to be found.
You need an array of TPoint, or sufficient raw memory allocated through Getmem(Pol, NumberOf Points * SizeOf(TPoint)).
You have to allocate the memory first. You can do that is several ways, but:

Code: Pascal  [Select][+][-]

1. var Pol: Array of TPoint;
2. ButtonRgn: THandle;
3.  
4. ...
5. begin
6.  Setlength(Pol,6);
7.   Pol[0].X := X-100; Pol[0].Y := Y-100;
8.   Pol[1].X := X-100; Pol[1].Y := Y+100;
9.   Pol[2].X := X+100; Pol[2].Y := Y+100;
10.   Pol[3].X := X+100; Pol[3].Y := Y-100;
11.   Pol[4].X := X; Pol[4].Y := Y-100;
12.   Pol[5].X := X-100; Pol[5].Y := Y-100;
13.  
14.   ButtonRgn := CreatePolygonRgn(@Pol[0], 6, WINDING);

I am not sure it works out of the box, but you get the point.
This should get you started anyway.

[balazsszekely]

CreatePolygonRgn works fine both under GTK2 and win32/64! The following example will draw a polygon to the form, then check if the user clicks inside/outside the shape:

Code: Pascal  [Select][+][-]

1. uses LCLIntf, LCLType;
2.  
3. var
4.   Rgn: THandle;
5.   Pol : array of TPoint;
6.  
7. procedure TForm1.FormCreate(Sender: TObject);
8. begin
9.   SetLength(Pol, 4);
10.   Pol[0].X := 120; Pol[0].Y := 75;
11.   Pol[1].X := 250; Pol[1].Y := 25;
12.   Pol[2].X := 300; Pol[2].Y := 200;
13.   Pol[3].X := 75;  Pol[3].Y := 125;
14.   Rgn := CreatePolygonRgn(@Pol[0], Length(Pol), WINDING);
15. end;
16.  
17. procedure TForm1.FormPaint(Sender: TObject);
18. begin
19.   with Form1.Canvas do
20.   begin
21.     Pen.Width := 2;
22.     Pen.Color := clBlack;
23.     Brush.Color := clRed;
24.     Canvas.Polygon(Pol);
25.   end;
26. end;
27.  
28. procedure TForm1.FormMouseDown(Sender: TObject; Button: TMouseButton;
29.   Shift: TShiftState; X, Y: Integer);
30. var
31.   Res: Boolean;  
32. begin
33.   Res := PtInRegion(Rgn, X, Y);
34.   if Res then
35.     ShowMessage('Clicked inside the polygon.')
36.   else
37.     ShowMessage('Clicked outside the polygon.');
38. end;
39.  

[Thaddy]

Yup. Works fine. He simply forgot to allocate memory.

[edit]
Because the button probably has a fixed shape he could also use a fixed sized array, not necessary to use a dynamic array.

[edgarrod71]

This doesn't work in Mac, what is the option for that?