A função Polygon desenha um polígono que consiste em dois ou mais vértices conectados por linhas retas. O polígono é descrito usando a caneta atual e preenchido usando o pincel atual e o modo de preenchimento de polígono.

#include <windows.h>
#include "resource.h"

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

int WINAPI WinMain(HINSTANCE hI, HINSTANCE hPI, PSTR szCL, int iCS) {
    static TCHAR szAppName[] = TEXT("AltWind");
    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(hI, IDI_ICON);
    wndclass.hCursor = LoadCursor(NULL, IDC_ARROW);
    wndclass.hbrBackground = (HBRUSH) GetStockObject(WHITE_BRUSH);
    wndclass.lpszMenuName  = NULL;
    wndclass.lpszClassName = szAppName;

    if(!RegisterClass(&wndclass)) {
        MessageBox(
            NULL,
            TEXT("Program requires Windows NT!"),
            szAppName,
            MB_ICONERROR
        );
        return 0;
    }
    hwnd = CreateWindow(
        szAppName, TEXT("Programação para Windows"), WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT, 500, 300,
        NULL, NULL, hI, NULL
    );

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

    while(GetMessage(&msg, NULL, 0, 0)) {
        TranslateMessage(&msg);
        DispatchMessage (&msg);
    }
    return msg.wParam;
}
LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wP, LPARAM lP) {
    static POINT aptFigure [10] = {
        10,70, 50,70, 50,10, 90,10, 90,50,
        30,50, 30,90, 70,90, 70,30, 10,30
    };
    static int cxClient, cyClient;
    HDC hdc;
    int i;
    PAINTSTRUCT ps;
    POINT apt[10];

    switch(msg) {
        case WM_SIZE:
            cxClient = LOWORD(lP);
            cyClient = HIWORD(lP);
            return 0;
        case WM_PAINT:
            hdc = BeginPaint(hwnd, &ps);
            SelectObject(hdc, GetStockObject(DKGRAY_BRUSH));
            for(i = 0; i < 10; i++) {
                apt[i].x = cxClient * aptFigure[i].x / 200;
                apt[i].y = cyClient * aptFigure[i].y / 100;
            }
            SetPolyFillMode(hdc, ALTERNATE);
            Polygon(hdc, apt, 10);
            for(i = 0; i < 10; i++) {
                apt[i].x += cxClient / 2;
            }
            SetPolyFillMode(hdc, WINDING);
            Polygon(hdc, apt, 10);
            EndPaint(hwnd, &ps);
            return 0;
        case WM_DESTROY:
            PostQuitMessage(0);
            return 0;
    }
    return DefWindowProc(hwnd, msg, wP, lP);
}