Windows程序编程GDI画十二等分圆

以下是使用GDI编写的绘制十二等分圆的Windows程序：

#include <windows.h>

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

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance,
                   PSTR szCmdLine, int iCmdShow)
{
    static TCHAR szAppName[] = TEXT("TwelveEqualPartsCircle");
    HWND hwnd;
    MSG msg;
    WNDCLASS wndclass;

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

    if (!RegisterClass(&wndclass))
    {
        MessageBox(NULL, TEXT("This program requires Windows NT!"),
                   szAppName, MB_ICONERROR);
        return 0;
    }

    hwnd = CreateWindow(szAppName, TEXT("Twelve Equal Parts Circle"),
                        WS_OVERLAPPEDWINDOW,
                        CW_USEDEFAULT, CW_USEDEFAULT,
                        CW_USEDEFAULT, CW_USEDEFAULT,
                        NULL, NULL, hInstance, NULL);

    ShowWindow(hwnd, iCmdShow);
    UpdateWindow(hwnd);

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

    return msg.wParam;
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    static int cxClient, cyClient;
    static POINT apt[13];

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

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

        for (int i = 1; i <= 12; i++)
        {
            apt[i].x = cxClient / 2 + (int)(0.4 * cxClient * sin(i * 30 * 3.14159 / 180));
            apt[i].y = cyClient / 2 - (int)(0.4 * cyClient * cos(i * 30 * 3.14159 / 180));
        }
        apt[13] = apt[1];

        return 0;

    case WM_PAINT:
        {
            PAINTSTRUCT ps;
            HDC hdc = BeginPaint(hwnd, &ps);

            SelectObject(hdc, GetStockObject(DC_PEN));
            SetDCPenColor(hdc, RGB(0, 0, 0));

            Polyline(hdc, apt, 13);

            EndPaint(hwnd, &ps);
        }
        return 0;

    case WM_DESTROY:
        PostQuitMessage(0);
        return 0;
    }

    return DefWindowProc(hwnd, message, wParam, lParam);
}

在该程序中，我们使用了以下GDI函数：

- `BeginPaint()`：获取设备环境句柄并准备绘制。
- `EndPaint()`：结束绘制并释放设备环境句柄。
- `SelectObject()`：选择一个GDI对象（比如画笔或画刷）并将其设置为设备环境的当前对象。
- `SetDCPenColor()`：设置设备环境的当前画笔颜色。
- `Polyline()`：绘制一系列直线段，连接一系列点。

程序中的`WM_SIZE`消息处理函数计算了十二等分圆上的每个点的坐标，并将它们保存在`apt`数组中。`WM_PAINT`消息处理函数使用`Polyline()`函数绘制这些点之间的线段，形成十二等分圆。