Cursor and Window position problem

I'm trying to create 2 windows and magnet them so they stay close to each other by 10px: the main window and bottom window. The bottom window act as a resizer for main window when user drag it.
Everything is fine with one problem: when main window is moved, the cursor points are not correct anymore. I posted below the pseudo code and a screenshot to show the effect problem.

Code:

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hwndMain = CreateWindow(L"classMain", L"main", WS_POPUP, 50, 0, 800, 600, NULL, NULL, instanceMain, NULL);
hwndResizer = CreateWindowEx(WS_EX_LAYERED, TEXT("classResizer"), L"", WS_POPUP, 400, 610, 55, 35, hwndMain, NULL, instanceMain, NULL);

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resizer proc

Code:

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case WM_LBUTTONUP: {
                ReleaseCapture();
        } break;

        case WM_LBUTTONDOWN: {
                SetCapture(hwndBottomResizer);
        } break;

        case WM_MOUSEMOVE: {

                if (wParam & MK_LBUTTON) {

                        RECT bottomResizerRect, mainWindowRect;
                        POINT posBottomResizer;
                       
                        GetWindowRect(hwndBottomResizer, &bottomResizerRect);
                        GetWindowRect(hwndMain, &mainWindowRect);

                        posBottomResizer.x = GET_X_LPARAM(lParam); //(int)(short)LOWORD(lParam);
                        posBottomResizer.y = GET_Y_LPARAM(lParam); //(int)(short)HIWORD(lParam);
                        ClientToScreen(hwndBottomResizer, &posBottomResizer);

                        HDWP move = BeginDeferWindowPos(2);
                        DeferWindowPos(move, hwndMain, 0, mainWindowRect.left, mainWindowRect.top, mainWindowRect.right - mainWindowRect.left, posBottomResizer.y, 0);
                        DeferWindowPos(move, hwndBottomResizer, 0, bottomResizerRect.left, posBottomResizer.y + 10, bottomResizerRect.right - bottomResizerRect.left, 35, 0);
                        EndDeferWindowPos(move);

                }

        } break;

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main proc

Code:

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        case WM_NCHITTEST: {

                moveWindows = DefWindowProc(hwnd, message, wParam, lParam);

                RECT rc, brc;

                GetWindowRect(hwnd, &rc);
                GetWindowRect(hwndBottomResizer, &brc);

                POINT pt;
                pt.x = GET_X_LPARAM(lParam);
                pt.y = GET_Y_LPARAM(lParam);
                ScreenToClient(hwnd, &pt);

                HDWP move = BeginDeferWindowPos(1);
                //DeferWindowPos(move, hwndMain, 0, mainWindowRect.left, mainWindowRect.top, mainWindowRect.right - mainWindowRect.left, posBottomResizer.y, 0);
                DeferWindowPos(move, hwndBottomResizer, 0, brc.left, rc.bottom + 10, brc.right - brc.left, 35, 0);
                EndDeferWindowPos(move);

                if (moveWindows == HTCLIENT) {
                        return HTCAPTION;
                }
                else {
                        return moveWindows;
                }
        } break;

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See below gif for effect problem.
https://ibb.co/TtTVZSM

Please watch this gif to see how the main window rect is losing control after is moved by bottom resizer
https://ibb.co/TtTVZSM

[Thread moved]

Quote:

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Originally Posted by Valerianel

Please watch this gif to see how the main window rect is losing control after is moved by bottom resizer
https://ibb.co/TtTVZSM

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Unfortunately it is not clear what you are doing and what for... :confused:
Could you explain it in more details?

I want to create a smaller window below main window to act as a resizer button. The problem is that when the main window is moved, the smaller window below it is not sending correct resize position anymore (like in gif animation). I guess this is because once the main window is moved the other window is not getting correct GetWindowRect positions for some reason

Quote:

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I guess this is because once the main window is moved the other window is not getting correct GetWindowRect positions for some reason

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Never guess with Windows programming! Do some debugging and find out. Determine what info you are getting and if not as expected, then understand what you are getting.