[Answered, no solution] GetFormImage on MacOS generates black bitmap

[wittbo]

Given this simple procedure:

procedure TmyForm.Button1Click(Sender: TObject);
var bm: TBitmap;
begin
   bm := myForm.GetFormImage;
   bm.Canvas.Changed;
   bm.SaveToFile('/users/myuser/downloads/test.bmp');
   bm.Free
end;

The file gets generated with the correct dimensions width and height, but the contents of the bitmap in the file is entirely black.
Any idea?
Does GetFormImage only work on Windows?

[lucamar]

Does GetFormImage only work on Windows?

No, it works also on Linux. See attached image, made using:

Code: Pascal  [Select][+][-]

1. procedure TMainForm.btDoTestClick(Sender: TObject);
2. var
3.   Bitmap: TBitmap;
4. begin
5.   Bitmap := GetFormImage;
6.   if Assigned(Bitmap) then
7.   try
8.     {Bitmap.Canvas.Changed; - not needed: there's no OnChange handler}
9.     Bitmap.SaveToFile('test.bmp');
10.     Image.Picture.LoadFromFile('test.bmp');
11.   finally
12.     Bitmap.Free;
13.   end;
14. end;

Unrelated, but note that it is very bad practice to reference the auto-created form instance inside the methods. If you realy need to reference the current object use Self, as in:
Self.GetFormImage

[bylaardt]

this reminds me of an old topic:
https://forum.lazarus.freepascal.org/index.php/topic,27896.msg173144.html#msg173144

[wittbo]

Sorry, but none of the solutions (GetFormimage, ...copyrect, ...) does work on MacOS. The Bitmap remains black.

I believe, it is a special MacOS problem(or cocoa): i will copy a link to this thread into the macos forum.

[bylaardt]

even paintto?

[wittbo]

Skalogryz wrote in the correspondent macos thread:  that's easy. The function has not been implemented for cocoa yet
https://forum.lazarus.freepascal.org/index.php/topic,45606.0.html

Therefore actually no solution for Mac users.

[bylaardt]

have you try?

Code: Pascal  [Select][+][-]

1. MyCapture:=TBitMap.Create(application);
2.   MyCapture.SetSize(ClientWidth,ClientHeight);
3.   MyCapture.canvas.FillRect(0,0,ClientWidth,ClientHeight);
4.   self.PaintTo(MyCapture.canvas,0,0);
5.   MyCapture.SaveToFile('/home/bylaardt/MyFormImage.bmp');
6.   MyCapture.free;

[wittbo]

Sorry, just tested.
But now the Image isn't black, now it's completely white.