setROP2(R2_XORPEN) win11下闪烁

Question

I have a program to draw a rubber band line, I use classic XOR , in Win32 GDI , this is SetROP2(R2_XORPEN) method, it works in xp/vista/win7/win8/win10 , but recently, after I update win11, found the rubber band line become flickering. this never happen before, is it a win11 bug? how to fix this?

I write a simple demo program, you can build and run it under win11 , and see flickering

note: I know handling WM_ERASEBKGND and using a double buffer can avoid window flickering, but this is only rubber band line flickering, not the entire window.

 #define WIN32_LEAN_AND_MEAN
 #include <windows.h>
 #include <tchar.h>
    
 LRESULT CALLBACK MyWndProc(HWND, UINT, WPARAM, LPARAM);
    
 int APIENTRY _tWinMain(_In_ HINSTANCE hInstance,
                      _In_opt_ HINSTANCE hPrevInstance,
                      _In_ LPWSTR    lpCmdLine,
                      _In_ int       nCmdShow)
 {
     UNREFERENCED_PARAMETER(hPrevInstance);
     UNREFERENCED_PARAMETER(lpCmdLine);
    
     WNDCLASSEX wcex;
     wcex.cbSize = sizeof(WNDCLASSEX);
     wcex.style = CS_HREDRAW | CS_VREDRAW;
     wcex.lpfnWndProc = MyWndProc;
     wcex.cbClsExtra = 0;
     wcex.cbWndExtra = 0;
     wcex.hInstance = hInstance;
     wcex.hIcon = NULL;
     wcex.hCursor = LoadCursor(nullptr, IDC_ARROW);
     wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
     wcex.lpszMenuName = NULL;
     wcex.lpszClassName = _T("MyRubberBandLine");
     wcex.hIconSm = NULL;
     RegisterClassEx(&wcex);
    
     HWND hWnd = CreateWindow(_T("MyRubberBandLine"), _T("RubberBandLine"), WS_OVERLAPPEDWINDOW,
         CW_USEDEFAULT, 0, CW_USEDEFAULT, 0, nullptr, nullptr, hInstance, nullptr);
    
     ShowWindow(hWnd, nCmdShow);
     UpdateWindow(hWnd);
    
     MSG msg;
     while (GetMessage(&msg, nullptr, 0, 0))
     {
         TranslateMessage(&msg);
         DispatchMessage(&msg);
     }
    
     return (int) msg.wParam;
 }
    
 //
 //  FUNCTION: WndProc(HWND, UINT, WPARAM, LPARAM)
 //
 //  PURPOSE: Processes messages for the main window.
 //
 //  WM_COMMAND  - process the application menu
 //  WM_PAINT    - Paint the main window
 //  WM_DESTROY  - post a quit message and return
 //
 //
 LRESULT CALLBACK MyWndProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
 {
     switch (message)
     {
     case WM_PAINT:
         {
             PAINTSTRUCT ps;
             HDC hdc = BeginPaint(hWnd, &ps);
    
             RECT rect;
             GetClientRect(hWnd, &rect);
             COLORREF clrbak = SetBkColor(hdc, RGB(255, 0, 0));
             ExtTextOut(hdc, 0, 0, ETO_OPAQUE, &rect, NULL, 0, NULL);
    
             int x = (rect.right - rect.left ) / 8;
             int y = (rect.bottom - rect.top) / 8;
             rect.left += x; rect.right -= x;
             rect.top += y; rect.bottom -= y;
             SetBkColor(hdc, RGB(0, 255, 0));
             ExtTextOut(hdc, 0, 0, ETO_OPAQUE, &rect, NULL, 0, NULL);
    
             rect.left += x; rect.right -= x;
             rect.top += y; rect.bottom -= y;
             SetBkColor(hdc, RGB(0, 0, 255));
             ExtTextOut(hdc, 0, 0, ETO_OPAQUE, &rect, NULL, 0, NULL);
    
             rect.left += x; rect.right -= x;
             rect.top += y; rect.bottom -= y;
             SetBkColor(hdc, RGB(0, 0, 0));
             ExtTextOut(hdc, 0, 0, ETO_OPAQUE, &rect, NULL, 0, NULL);
    
             SetBkColor(hdc, clrbak);
             EndPaint(hWnd, &ps);
         }
         break;
     case WM_DESTROY:
         PostQuitMessage(0);
         break;
     case WM_MOUSEMOVE:
         {
            static POINT ptPrev1{ -1,-1 };
            static POINT ptPrev2{ -1,-1 };
    
            HDC hdc = GetDC(hWnd);
            int modebak = SetROP2(hdc, R2_XORPEN);
    
            HPEN hPen = CreatePen(PS_SOLID, 1, RGB(255, 255, 255));
            HGDIOBJ hOld = SelectObject(hdc, hPen);
    
            // erase prev line
            if (ptPrev1.x != -1 && ptPrev2.x != -1)
            {
                MoveToEx(hdc, ptPrev1.x, ptPrev1.y, NULL);
                LineTo(hdc, ptPrev2.x, ptPrev2.y);
                ptPrev1.x = ptPrev1.y = ptPrev2.x = ptPrev2.y = -1;
            }
    
            // draw new line
            RECT rect;
            GetClientRect(hWnd, &rect);
            POINT ptCenter{ (rect.left + rect.right) / 2, (rect.top + rect.bottom) / 2 };
            POINT ptMouse{ LOWORD(lParam), HIWORD(lParam) };
            if ((ptMouse.x != ptCenter.x) || (ptMouse.y != ptCenter.y))
            {
                MoveToEx(hdc, ptCenter.x, ptCenter.y, NULL);
                LineTo(hdc, ptMouse.x, ptMouse.y);
    
                ptPrev1 = ptCenter;
                ptPrev2 = ptMouse;
            }
    
            SelectObject(hdc, hOld);
            SetROP2(hdc, modebak);
            ReleaseDC(hWnd, hdc);
            DeleteObject(hPen);
         }
         break;
     default:
         return DefWindowProc(hWnd, message, wParam, lParam);
     }
     return 0;
 }

Answer 1

You are right. Drawing lines using SetROP2(hdc, R2_XORPEN) where hdc is device context of the window generally causes flickering. However, the flickering is almost negligible under Windows 7 and Windows 10. The flickering is much more noticeable with Windows 11. Instead of drawing in hdc, which is device context of the window, draw in compatible memory device context (hMemDC=CreateCompatibleDC(hdc);) and just BitBlt(hdc,0,0...) hMemDC to hdc. You will not lose speed of drawing and flickering is completely eliminated.