Windows程序编程GDI在一个圆上均匀地平分12个点，并将这些点相互连线

以下是Windows程序编程中使用GDI在一个圆上均匀地平分12个点，并将这些点相互连线的示例代码：

#include <windows.h>

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam);

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
{
    WNDCLASSEX wcex;
    HWND hWnd;
    MSG msg;

    // 注册窗口类
    ZeroMemory(&wcex, sizeof(wcex));
    wcex.cbSize = sizeof(WNDCLASSEX);
    wcex.style = CS_HREDRAW | CS_VREDRAW;
    wcex.lpfnWndProc = WndProc;
    wcex.hInstance = hInstance;
    wcex.hCursor = LoadCursor(NULL, IDC_ARROW);
    wcex.lpszClassName = "MyWindowClass";
    RegisterClassEx(&wcex);

    // 创建窗口
    hWnd = CreateWindow("MyWindowClass", "GDI Demo", WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT, 640, 480, NULL, NULL, hInstance, NULL);
    if (!hWnd)
    {
        return FALSE;
    }

    // 显示窗口
    ShowWindow(hWnd, nCmdShow);
    UpdateWindow(hWnd);

    // 消息循环
    while (GetMessage(&msg, NULL, 0, 0))
    {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return (int)msg.wParam;
}

LRESULT CALLBACK WndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    PAINTSTRUCT ps;
    HDC hdc;
    int centerX, centerY, radius, i;
    double angle;
    POINT points[12];

    switch (message)
    {
    case WM_PAINT:
        hdc = BeginPaint(hWnd, &ps);

        // 获取窗口中心坐标和圆半径
        centerX = ps.rcPaint.right / 2;
        centerY = ps.rcPaint.bottom / 2;
        radius = min(centerX, centerY) - 50;

        // 计算12个点的坐标
        for (i = 0; i < 12; i++)
        {
            angle = i * 2 * 3.1415926 / 12;
            points[i].x = centerX + (int)(radius * cos(angle));
            points[i].y = centerY - (int)(radius * sin(angle));
        }

        // 依次连接所有点
        MoveToEx(hdc, points[0].x, points[0].y, NULL);
        for (i = 1; i < 12; i++)
        {
            LineTo(hdc, points[i].x, points[i].y);
        }
        LineTo(hdc, points[0].x, points[0].y);

        EndPaint(hWnd, &ps);
        break;

    case WM_DESTROY:
        PostQuitMessage(0);
        break;

    default:
        return DefWindowProc(hWnd, message, wParam, lParam);
    }

    return 0;
}

在上述示例代码中，我们在窗口的客户区中心绘制了一个圆，并在该圆上均匀地平分12个点。然后，我们通过依次连接这些点来绘制圆的边界。其中，我们使用了三角函数求出每个点的坐标，并使用GDI的MoveToEx和LineTo函数连接这些点。最终，我们得到了一个包含12边的正多边形，即一个正十二边形。