第5章，[Win32 章节] ：圆角矩形教学插图绘制程序-开发者社区

/*------------------------------------------------------------ RoundRect 函数讲解插图 水饺编程，2026 ------------------------------------------------------------*/ #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("RoundRect_Teach"); 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("注册窗口类失败！"), szAppName, MB_ICONERROR); return 0; } hwnd = CreateWindow(szAppName, // window class name TEXT("RoundRect 绘图讲解图示"), // window caption WS_OVERLAPPEDWINDOW, // window style CW_USEDEFAULT, // initial x position CW_USEDEFAULT, // initial y position CW_USEDEFAULT, // initial x size CW_USEDEFAULT, // initial y size NULL, // parent window handle NULL, // window menu handle hInstance, // program instance handle NULL); // creation parameters 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) { HDC hdc; PAINTSTRUCT ps; RECT rect; static int xLeft, xRight, yTop, yBottom; static int xCornerEllipse, yCornerEllipse; COLORREF color; HPEN hPen, hOldPen; HBRUSH hBrush, hOldBrush; switch (message) { case WM_CREATE: xLeft = 100; xRight = 600; yTop = 100; yBottom = 500; xCornerEllipse = 160; yCornerEllipse = 120; return 0; case WM_PAINT: hdc = BeginPaint(hwnd, &ps); color = RGB(255, 0, 255); hPen = CreatePen(PS_DASH, 0, color); hOldPen = (HPEN)SelectObject(hdc, hPen); Rectangle(hdc, xLeft, yTop, xRight, yBottom); SelectObject(hdc, hOldPen); DeleteObject(hPen); color = RGB(255, 0, 0); hPen = CreatePen(PS_DASH, 0, color); hOldPen = (HPEN)SelectObject(hdc, hPen); Ellipse(hdc, xLeft, yTop, xLeft + xCornerEllipse, yTop + yCornerEllipse); Ellipse(hdc, xRight - xCornerEllipse, yTop, xRight, yTop + yCornerEllipse); Ellipse(hdc, xLeft, yBottom - yCornerEllipse, xLeft + xCornerEllipse, yBottom); Ellipse(hdc, xRight - xCornerEllipse, yBottom - yCornerEllipse, xRight, yBottom); SelectObject(hdc, hOldPen); DeleteObject(hPen); hBrush = (HBRUSH)GetStockObject(NULL_BRUSH); hOldBrush = (HBRUSH)SelectObject(hdc, hBrush); color = RGB(0, 0, 255); hPen = CreatePen(PS_SOLID, 0, color); hOldPen = (HPEN)SelectObject(hdc, hPen); RoundRect(hdc, xLeft, yTop, xRight, yBottom, xCornerEllipse, yCornerEllipse); SelectObject(hdc, hOldPen); DeleteObject(hPen); SelectObject(hdc, hOldBrush); EndPaint(hwnd, &ps); return 0; case WM_DESTROY: PostQuitMessage(0); return 0; } return DefWindowProc(hwnd, message, wParam, lParam); }

代码本身不难，不过呢，我还是得提醒两句。

第一点，对于 static ，有它在，我们才可以在 WM_CREATE 消息中初始化一些个变量，而在 WM_PAINT 消息中使用 WM_CREATE 消息中的初始化值。

不同的消息，是处在不同的窗口过程函数 WinProc 的调用之中的。要想在不同的 WinProc 函数的调用中使用同一个变量的值，则需要将相关变量设置为 static 属性。

第二点，在本程序中，画刷我们使用了一次，并且使用的是备用画刷 NULL_BRUSH 。备用画刷也好，备用画笔也好，用完了，需要将其选出设备环境，但是不能删除它。而对于自定义画笔和自定义画刷，则需要在用完以后，选出设备环境，然后再删除它。