flickering in GDI drawing under win11

Question

hello, i have a program to draw a rubber band line, i use classic XOR, in Win32 GDI, this is SetROP2(R2_XORPEN) method, it workd 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? thanks!

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

#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

Hi. Thank you for your question and reaching out. My name is John and I’d be more than happy to help you with your query.

As what Raymond Chen on this thread https://stackoverflow.com/questions/7633672/how-to-avoid-excessive-screen-flickering-with-gdi

Your WM PAINT should write to the window DC precisely once to reduce flicker. This single operation is typically a BitBlt:

HDC hdc = BeginPaint(m_hwnd, &m_PaintStruct);
... paint to bitmap ...
BitBlt(hdc, ...); // blt from bitmap to screen
EndPaint(m_hwnd, &m_PaintStruct);

If the reply was helpful, please don’t forget to upvote or accept as answer, thank you.

Answer 2

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