Canvas does not allow drawing - delphi

Question

I want to Draw a Screenshot from the entire screen to a TForm1 Canvas.
This code works well in Delphi XE3
procedure TForm1.Button1Click(Sender: TObject);
var
c,scr: TCanvas;
r,r2: TRect;
begin
c := TCanvas.Create;
scr := TCanvas.Create;
c.Handle := GetWindowDC(GetDesktopWindow);
try
r := Rect(0, 0, 200, 200);
form1.Canvas.CopyRect(r, c, r);
finally
ReleaseDC(0, c.Handle);
c.Free;
end;
Now I want to copy the screenshot to another canvas first.
Is there a way to do this without getting this error?
procedure TForm1.Button1Click(Sender: TObject);
var
c,scr: TCanvas;
r,r2: TRect;
begin
c := TCanvas.Create;
scr := TCanvas.Create;
c.Handle := GetWindowDC(GetDesktopWindow);
try
r := Rect(0, 0, 200, 200);
scr.CopyRect(r,c,r); <-- Error, canvas does not allow drawing
form1.Canvas.CopyRect(r, scr, r); <-- Error, canvas does not allow drawing
finally
ReleaseDC(0, c.Handle);
c.Free;
end;

Answer 1

If you need to work with an additional canvas you will have to assign a HDC e.g.
var
WindowHandle:HWND;
ScreenCanvas,BufferCanvas: TCanvas;
r,r2: TRect;
ScreenDC,BufferDC :HDC;
BufferBitmap : HBITMAP;
begin
WindowHandle := 0;
ScreenCanvas := TCanvas.Create;
BufferCanvas := TCanvas.Create;
ScreenDC:=GetWindowDC(WindowHandle);
ScreenCanvas.Handle := ScreenDC;
BufferDC := CreateCompatibleDC(ScreenDC);
BufferCanvas.Handle := BufferDC;
BufferBitmap := CreateCompatibleBitmap(ScreenDC,
GetDeviceCaps(ScreenDC, HORZRES),
GetDeviceCaps(ScreenDC, VERTRES));
SelectObject(BufferDC, BufferBitmap);
try
r := Rect(0, 0, 200, 200);
BufferCanvas.CopyRect(r,ScreenCanvas,r);
form1.Canvas.CopyRect(r, BufferCanvas, r);
finally
ReleaseDC(WindowHandle, ScreenCanvas.Handle);
DeleteDC(BufferDC);
DeleteObject(BufferBitmap);
BufferCanvas.Free;
ScreenCanvas.Free;
end;
end;

Answer 2

It's a time to toss my solution into the pot!
procedure TForm1.FormClick(Sender: TObject);
var
ScreenCanvas: TCanvas;
begin
ScreenCanvas := TCanvas.Create;
try
ScreenCanvas.Handle := GetWindowDC(GetDesktopWindow);
Win32Check(ScreenCanvas.HandleAllocated);
Canvas.CopyRect(Canvas.ClipRect, ScreenCanvas, ScreenCanvas.ClipRect);
finally
ReleaseDC(GetDesktopWindow, ScreenCanvas.Handle);
ScreenCanvas.Free;
end;
end;