procedure GetDisplayScale(DevHandle: THandle; IsPrinterHandle: Boolean; var aScaleX, aScaleY: Extended);
{$IFNDEF FPC}
var
  DevMode: TDevMode;
{$ENDIF}
begin
  aScaleX := GetDeviceCaps(DevHandle, LOGPIXELSX) / 96;
  aScaleY := GetDeviceCaps(DevHandle, LOGPIXELSY) / 96;
  if (Abs(aScaleX - 1) > 1e-4) and (Abs(aScaleY - 1) > 1e-4) or IsPrinterHandle then
    Exit;
  // scale factor for non DPI aware applications
  // msdn.microsoft.com/en-us/library/windows/desktop/dn469266(v=vs.85).aspx
{$IFNDEF FPC}
  ZeroMemory(@DevMode, sizeof(DevMode));
  if EnumDisplaySettings(nil, Cardinal(-1{ENUM_CURRENT_SETTINGS MSDN FLAG}), DevMode) then
  begin
    aScaleX := 1 / (DevMode.dmPelsWidth / GetSystemMetrics(SM_CXSCREEN));
    aScaleY := 1 / (DevMode.dmPelsHeight / GetSystemMetrics(SM_CYSCREEN));
  end;
{$ENDIF}
end;