Delphi PureAPIWindow program

program PureAPIWindow;
uses
SysUtils,
Windows,
Messages;
const
WinClassName = 'DvsClass';
StrOut = 'Davis TextOut';
//´°¿Ú»Øµ÷º¯Êý
function MyWinProc(
hWindow: HWND;
aMessage: UINT;
WParam: WPARAM;
LParam: LPARAM): LRESULT; stdcall; export;
var
dc: HDC;
ps: TPaintStruct;
rect: TRect;
begin
MyWinProc := 0;
case aMessage of
WM_PAINT:
begin
dc := BeginPaint(hWindow,ps);
GetClientRect(hWindow,rect);
DrawText(dc,StrOut,Length(StrOut),rect,DT_SINGLELINE or DT_CENTER or DT_VCENTER);
//TextOut(dc,0,0,StrOut,Length(StrOut));
EndPaint(hWindow,ps);
end;
WM_LBUTTONDOWN:
begin
dc := GetDC(hWindow);//GetDC(0);
TextOut(dc,0,0,'Left Button Down',Length('Left Button Down'));
ReleaseDC(hWindow,dc);
//ReleaseDC(0,dc);
end;
WM_CLOSE:
if ID_YES = MessageBox(0,'Are you sure exit ?','Propmt info',MB_YESNO) then
begin
DestroyWindow(hWindow);
end;
WM_DESTROY:
begin
PostQuitMessage(0);
end;
else
Result := DefWindowProc(hWindow,aMessage,WParam,LParam);
end;
end;
function WinRegister: Boolean;
var
wndClass: TWndClass;
hInstance: Cardinal;
begin
hInstance := GetModuleHandle(0);
//
wndClass.style := CS_VREDRAW or CS_HREDRAW;
wndClass.lpfnWndProc := TFNWndProc(@MyWinProc); //Callback function
wndClass.cbClsExtra := 0;
wndClass.cbWndExtra := 0;
wndClass.hInstance := hInstance;//Same as System.MainInstance; //ʵÀý¾ä±ú
wndClass.hIcon := LoadIcon(0,IDI_INFORMATION);
wndClass.hCursor := LoadCursor(0,IDC_CROSS);
wndClass.hbrBackground := HBRUSH(GetStockObject(BLACK_BRUSH));
wndClass.lpszMenuName := nil;
wndClass.lpszClassName := WinClassName;
//
Result := Windows.RegisterClass(wndClass) <> 0;
end;
function WinCreate: HWND;
var
hWindow: HWND;
hInstance: Cardinal;
begin
hInstance := GetModuleHandle(0);
hWindow := C