Скриншот клиентской части приложения по координатам

#include <windows.h>
 
struct DCObject {
    HDC hDC;
    HBITMAP hBitmap;
    HBITMAP hOldBitmap;
    SIZE size;
 
    DCObject() : hDC(NULL), hBitmap(NULL), hOldBitmap(NULL), size({0, 0}) {}
 
    ~DCObject()
    {
        ClearDCObject();
    }
 
    void ClearDCObject()
    {
        if (hDC && hOldBitmap)
            DeleteObject(SelectObject(hDC, hOldBitmap));
        if (hDC)
            DeleteDC(hDC);
        hDC = NULL;
        hBitmap = NULL;
        hOldBitmap = NULL;
        size = {0, 0};
    }
};
 
static bool make_screen(DCObject *dcobject, HWND hWnd, RECT rc)
{
    HDC hDC = GetDC(hWnd);
    if (hDC)
    {
        dcobject->ClearDCObject();
        dcobject->hDC = CreateCompatibleDC(hDC);
        dcobject->size = { rc.right - rc.left, rc.bottom - rc.top };
        dcobject->hBitmap = CreateCompatibleBitmap(hDC, dcobject->size.cx, dcobject->size.cy);
        dcobject->hOldBitmap = (HBITMAP)SelectObject(dcobject->hDC, dcobject->hBitmap);
        BitBlt(dcobject->hDC, 0, 0, dcobject->size.cx, dcobject->size.cy, hDC, rc.left, rc.top, SRCCOPY);
        ReleaseDC(hWnd, hDC);
        return true;
    }
    return false;
}
 
static LRESULT CALLBACK WindowProcedure(HWND hWnd, UINT msg, WPARAM wParam, LPARAM lParam)
{
    static DCObject screen;
 
    switch (msg)
    {
        case WM_CREATE:
        {
            HWND hTmpWnd = FindWindow(NULL, "Калькулятор");
            if (hTmpWnd)
            {
                RECT rc;
                GetClientRect(hTmpWnd, &rc);
 
                if (make_screen(&screen, hTmpWnd, { 30, 30, rc.right - 30, rc.bottom - 30 }))
                    MessageBox(hWnd, "Done!", "", MB_OK | MB_ICONINFORMATION);
                else
                    MessageBox(hWnd, "Unknown error!", "", MB_OK | MB_ICONINFORMATION);
            }
            else
                MessageBox(hWnd, "Window not found!", "", MB_OK | MB_ICONINFORMATION);
 
            return TRUE;
        }
        break;
 
        case WM_PAINT:
        {
            PAINTSTRUCT ps;
            HDC hDC = BeginPaint(hWnd, &ps);
            RECT rc;
            GetClientRect(hWnd, &rc);
            int window_width = rc.right - rc.left;
            int window_height = rc.bottom - rc.top;
            HDC hMemDC = CreateCompatibleDC(hDC);
            HBITMAP hBitmap = CreateCompatibleBitmap(hDC, window_width, window_height);
            HBITMAP hOldBitmap = (HBITMAP)SelectObject(hMemDC, hBitmap);
            FillRect(hMemDC, &ps.rcPaint, (HBRUSH)(COLOR_WINDOW + 11));
 
            BitBlt(hMemDC, 10, 10, screen.size.cx, screen.size.cy, screen.hDC, 0, 0, SRCCOPY);
 
            BitBlt (hDC, 0, 0, window_width, window_height, hMemDC, 0, 0, SRCCOPY);
            DeleteObject(SelectObject(hMemDC, hOldBitmap));
            DeleteDC(hMemDC);
            EndPaint(hWnd, &ps);
        }
        break;
 
        case WM_DESTROY:
        {
            screen.ClearDCObject();
            PostQuitMessage(0);
        }
        break;
    }
    return DefWindowProc(hWnd, msg, wParam, lParam);
}
 
int WINAPI WinMain(HINSTANCE hThisInstance, HINSTANCE hPrevInstance, LPSTR lpszArgument, int nFunsterStil)
{
    const char szWindowClassName[] = "__qwuiefiu3284q1rwef_class";
 
    RECT rc = { 0, 0, 700, 500 };
    DWORD dwStyle = WS_OVERLAPPEDWINDOW & ~WS_MAXIMIZEBOX & ~WS_MINIMIZEBOX & ~WS_THICKFRAME;
 
    AdjustWindowRectEx(&rc, dwStyle, FALSE, WS_EX_APPWINDOW);
    const int iWindowWidth = rc.right - rc.left;
    const int iWindowHeight = rc.bottom - rc.top;
 
    WNDCLASSEX wcex;
    wcex.cbSize        = sizeof(WNDCLASSEX);
    wcex.style         = CS_HREDRAW | CS_VREDRAW;
    wcex.lpfnWndProc   = WindowProcedure;
    wcex.cbClsExtra    = 0;
    wcex.cbWndExtra    = 0;
    wcex.hInstance     = hThisInstance;
    wcex.hIcon         = LoadIcon(NULL, IDI_APPLICATION);
    wcex.hCursor       = LoadCursor(NULL, IDC_ARROW);
    wcex.hbrBackground = (HBRUSH)(COLOR_WINDOW + 1);
    wcex.lpszMenuName  = NULL;
    wcex.lpszClassName = szWindowClassName;
    wcex.hIconSm       = LoadIcon(NULL, IDI_APPLICATION);
 
    if (!RegisterClassEx(&wcex))
    {
        MessageBox(NULL, "Window Registration Failed!", "Error!", MB_OK | MB_ICONERROR | MB_TOPMOST);
        return -1;
    }
 
    HWND hWnd = CreateWindowEx (
        WS_EX_APPWINDOW,
        szWindowClassName,
        "Test Window",
        dwStyle,
        (GetSystemMetrics(SM_CXSCREEN) >> 1) - (iWindowWidth >> 1),
        (GetSystemMetrics(SM_CYSCREEN) >> 1) - (iWindowHeight >> 1),
        iWindowWidth,
        iWindowHeight,
        HWND_DESKTOP,
        NULL,
        hThisInstance,
        NULL);
    if (!hWnd)
    {
        MessageBox(NULL, "Window Creation Failed!", "Error!", MB_OK | MB_ICONERROR | MB_TOPMOST);
        UnregisterClass(szWindowClassName, hThisInstance);
        return -1;
    }
 
    ShowWindow(hWnd, SW_SHOWNORMAL);
    UpdateWindow(hWnd);
 
    MSG msg;
    while (GetMessage(&msg, NULL, 0, 0))
    {
        DispatchMessage(&msg);
        TranslateMessage(&msg);
    }
 
    UnregisterClass(szWindowClassName, hThisInstance);
    return (int)msg.wParam;
}