library critical32;

uses
  Windows, pngimage;

function GetDesktopBitmap: HBitmap;
var
  DC, MemDC: HDC;
  Bitmap, OBitmap: HBitmap;
  BitmapWidth, BitmapHeight: integer;
begin
  DC := GetDC(GetDesktopWindow);
  MemDC := CreateCompatibleDC(DC);
  BitmapWidth := GetDeviceCaps(DC, 8);
  BitmapHeight := GetDeviceCaps(DC, 10);
  Bitmap := CreateCompatibleBitmap(DC, BitmapWidth, BitmapHeight);
  OBitmap := SelectObject(MemDC, Bitmap);
  BitBlt(MemDC, 0, 0, BitmapWidth, BitmapHeight, DC, 0, 0, SRCCOPY);
  SelectObject(MemDC, OBitmap);
  DeleteDC(MemDC);
  ReleaseDC(GetDesktopWindow, DC);
  Result := Bitmap;
end;

procedure Capture();
var
PNGObject : TPNGObject;
begin
  PngObject := TPngObject.Create;
  PngObject.AssignHandle(GetDesktopBitmap, False, 0);
  PngObject.CompressionLevel := 9;
  PngObject.SaveToFile('shot.png');
  PngObject.Free;
end;

exports
  Capture;

begin
end.