我尝试在WM_CREATE消息中设置首选的设备上下文属性,然后在WM_PAINT消息中使用它。我的方法是分别在SaveDCRestoreDC消息中使用WM_CREATEWM_PAINT函数。但是结果不符合我的需要。我真正需要的是在客户区域的中心显示一个圆圈。

#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 ("HelloWin") ;
     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,                  // window class name
                          TEXT ("The Hello Program"), // 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 nSavedDC;

     switch (message)
     {
     case WM_CREATE:
         hdc = GetDC(hwnd);
         SetMapMode(hdc, MM_LOMETRIC);
         GetClientRect(hwnd, &rect);
         SetViewportOrgEx(hdc, rect.right/2, rect.bottom/2, NULL);
         nSavedDC = SaveDC(hdc);         //I want to save the current state of device context to be used in WM_PAINT message.
         ReleaseDC(hwnd, hdc);
         return 0;

     case WM_PAINT:
          hdc = BeginPaint (hwnd, &ps) ;
          RestoreDC(hdc, nSavedDC);       //Restore the the state of device context which is saved in WM_CREATE message.
          Ellipse(hdc, -100, 100, 100, -100);
          EndPaint (hwnd, &ps) ;
          return 0 ;

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

最佳答案

您的代码缺乏错误处理。您需要检查每个GDI函数调用返回的所有值。

MSDN page所述,SaveDC / RestoreDC的用途主要是在完成绘制后将状态恢复为原始状态。这正是您在WM_CREATEWM_PAINT消息处理程序中都没有执行的操作。您始终将DC保留为修改状态。

至于使用SaveDC / RestoreDC一次设置DC状态,然后在每次绘制操作时快速恢复它,而不是每次都从头开始设置它,我至少想到了一个障碍:如果某些其他函数在在处理程序之间的DC还原项目(不在DC状态堆栈的顶部)之间,则保存在堆栈顶部的状态将被破坏,如here所述。

关于c - 不能在不同的消息处理代码中使用“SaveDC”和“RestoreDC”功能吗?,我们在Stack Overflow上找到一个类似的问题:https://stackoverflow.com/questions/44610963/

10-11 23:08
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