Linguagem C/C++ PolyBezier, MoveToEx, LineTo

#include <windows.h>

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);


int WINAPI WinMain(HINSTANCE hI, HINSTANCE hPI, PSTR szCmdLine, int iCS) {

    static TCHAR szAppName[] = TEXT("Desenho");
    HWND     hwnd;
    MSG      msg;
    WNDCLASS wndclass;

    wndclass.style         = CS_HREDRAW | CS_VREDRAW;
    wndclass.lpfnWndProc   = WndProc;
    wndclass.cbClsExtra    = 0;
    wndclass.cbWndExtra    = 0;
    wndclass.hInstance     = hI;
    wndclass.hIcon         = LoadIcon(NULL, IDI_APPLICATION);
    wndclass.hCursor       = LoadCursor(NULL, IDC_ARROW);
    wndclass.hbrBackground = GetStockObject(WHITE_BRUSH);
    wndclass.lpszMenuName  = NULL;
    wndclass.lpszClassName = szAppName;

    if(!RegisterClass(&wndclass)) {
        MessageBox(NULL,TEXT("W.NT foi requerido!"),szAppName,MB_ICONERROR);
        return 0;
    }

    hwnd = CreateWindow(
        szAppName, TEXT("Linha"), WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,
        NULL, NULL, hI, NULL
    );

    ShowWindow(hwnd, iCS);
    UpdateWindow(hwnd);

    while(GetMessage(&msg, NULL, 0, 0)) {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }
    return msg.wParam;
}

void DrawBezier(HDC hdc, POINT apt[]) {
    PolyBezier(hdc, apt, 4);

    MoveToEx(hdc, apt[0].x, apt[0].y, NULL);
    LineTo  (hdc, apt[1].x, apt[1].y);

    MoveToEx(hdc, apt[2].x, apt[2].y, NULL);
    LineTo(hdc, apt[3].x, apt[3].y);
}

LRESULT CALLBACK WndProc(HWND hwnd,UINT message,WPARAM wParam,LPARAM lParam) {
    static      POINT apt[4];
    HDC         hdc;
    int         cxClient, cyClient;
    PAINTSTRUCT ps;

    switch(message) {
        case WM_SIZE:
            cxClient = LOWORD(lParam);
            cyClient = LOWORD(lParam);

            apt[0].x = cxClient /4;
            apt[0].y = cyClient /2;

            apt[1].x = cxClient/2;
            apt[1].y = cyClient/4;

            apt[2].x = cxClient/2;
            apt[2].y = 3 * cyClient/4;

            apt[3].x = 3 * cxClient/4;
            apt[3].y = cyClient/2;

            return 0;

        case WM_LBUTTONDOWN:
        case WM_RBUTTONDOWN:
        case WM_MOUSEMOVE:
            if(wParam & MK_LBUTTON || wParam & MK_RBUTTON) {
                hdc = GetDC(hwnd);
                SelectObject(hdc, GetStockObject(WHITE_PEN));
                DrawBezier(hdc, apt);

                if(wParam & MK_LBUTTON) {
                    apt[1].x = LOWORD(lParam);
                    apt[1].y = HIWORD(lParam);
                }

                if(wParam & MK_RBUTTON) {
                    apt[2].x = LOWORD(lParam);
                    apt[2].y = HIWORD(lParam);
                }

                SelectObject(hdc, GetStockObject(BLACK_PEN));
                DrawBezier(hdc, apt);
                ReleaseDC(hwnd, hdc);
            }
            return 0;

        case WM_PAINT:
            InvalidateRect(hwnd, NULL, TRUE);
            hdc = BeginPaint(hwnd, &ps);
            DrawBezier(hdc, apt);
            EndPaint(hwnd, &ps);
            return 0;

        case WM_DESTROY:
            PostQuitMessage(0);
            return 0;
    }
    return DefWindowProc(hwnd, message, wParam, lParam);
}