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Editorial Team
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Asked: 2026-06-17T06:59:07+00:00

I handle the WM_NCCALCSIZE message, and try to set the dest window client rect

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I handle the WM_NCCALCSIZE message, and try to set the dest window client rect manually.

case WM_NCCALCSIZE: 
        {
            RECT *rect = (LPRECT)lParam;
            if (wParam == TRUE)
            {
                ////缩小客户区的范围
                //RECT *rect = (LPRECT)lParam;
                //rect->left += 8;
                //rect->right -= 8;
                //rect->top += 30;
                //rect->bottom = 8;
                InflateRect(rect, -50, -50);
                RECT dstRect = *(LPRECT)lParam;
                RECT srcRect = rect[1];
                rect[1] = dstRect;
                rect[2] = srcRect;

                //DefWindowProc(hWnd, message, wParam, lParam);
                return 0;
                //return WVR_REDRAW;
            }
            else
            {
                DWORD lRet =  DefWindowProc(hWnd, message, wParam, lParam);
                return lRet;
            }

But the result is bad, enter image description here
When I resize the window the text drawn with DrawText does not get erased cleanly.

How do I erase the background completely?

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1 Answer

  1. Editorial Team

    The root cause here is if you changed the client size, you changed the non-client area size.
    But WM_ERASEBKGND handler does only erase the client area background but not non-client area size.

    So, if you changed the client size, you’ll also need to handle the WM_NCPAINT to erase the non-client area background and paint the frame with DefWindowProc.

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