テトリスをつくりたいが,うまく描画できない

質問内容

Win32APIでテトリスを作ろうとして背景の描画に取り組んでいるのですが,
以下のコードだとうまくいきません。

C
1#include <windows.h>
2
3LRESULT CALLBACK WndProc(HWND hwnd , UINT msg , WPARAM wp , LPARAM lp) {
4	HDC hdc;
5	PAINTSTRUCT ps;
6
7	static BYTE count1 , count2;
8	static POINT po1[22];
9	static CONST DWORD dw[22] = {
10		2 , 2 , 2 , 2 , 2 , 2 , 2 , 2 , 2 , 2 , 2
11	};
12
13	switch (msg) {
14	case WM_DESTROY:
15		PostQuitMessage(0);
16		return 0;
17	case WM_CREATE:
18		for(count1 = 0 , count2 = 10 ; count1 < 22 ; count1++ , count2 += 30) {
19			po1[count1].x = count2;
20			po1[count1].y = 10;
21			po1[++count1].x = count2;
22			po1[count1].y = 360;
23		}
24	case WM_PAINT:
25		hdc = BeginPaint(hwnd , &ps);
26		PolyPolyline(hdc , po1 , dw , 11);
27		EndPaint(hwnd , &ps);
28		return 0;
29	}
30	return DefWindowProc(hwnd , msg , wp , lp);
31}
32
33int WINAPI WinMain(HINSTANCE hInstance , HINSTANCE hPrevInstance ,
34			PSTR lpCmdLine , int nCmdShow ) {
35	HWND hwnd;
36	MSG msg;
37	WNDCLASS winc;
38
39	winc.style		= CS_HREDRAW | CS_VREDRAW;
40	winc.lpfnWndProc	= WndProc;
41	winc.cbClsExtra	= winc.cbWndExtra	= 0;
42	winc.hInstance		= hInstance;
43	winc.hIcon		= LoadIcon(NULL , IDI_APPLICATION);
44	winc.hCursor		= LoadCursor(NULL , IDC_ARROW);
45	winc.hbrBackground	= (HBRUSH)GetStockObject(WHITE_BRUSH);
46	winc.lpszMenuName	= NULL;
47	winc.lpszClassName	= TEXT("TETRIS");
48
49	if (!RegisterClass(&winc)) return -1;
50
51	hwnd = CreateWindow(
52			TEXT("TETRIS") , TEXT("TETRIS") ,
53			WS_OVERLAPPEDWINDOW | WS_VISIBLE ,
54			CW_USEDEFAULT , CW_USEDEFAULT ,
55			CW_USEDEFAULT , CW_USEDEFAULT ,
56			NULL , NULL , hInstance , NULL
57	);
58
59	if (hwnd == NULL) return -1;
60
61	while(GetMessage(&msg , NULL , 0 , 0)) DispatchMessage(&msg);
62	return msg.wParam;
63}
64