Hi EVERY ONE.
I'm working on a title-bar free window on windows api based on this example

ukmKN.png

But i want to resize window outside of it's window area just like windows 10 style :

4Q9NL.png

What should i do? or where should i start ?

Code:
#pragma once
#include <memory>
#include <string>
#include <Windows.h>

using unique_hwnd = std::unique_ptr<std::remove_pointer <HWND>::type, decltype(&DestroyWindow)>;

class Window
{
public:
    Window();
    HWND handle() const { return hWnd.get(); }
    bool isClosed() const { return _closed; };

private:
    unique_hwnd hWnd;
    bool _closed = false;

    static const std::wstring& registerWindow();
    static LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wparam, LPARAM lparam);

    void setBorderLess() const;
    void show() const;
    void setShadow() const;
};

Code:
#include "test.h"
#include <cassert>
#include <stdexcept>
#include <windowsx.h>
#include <dwmapi.h>
#pragma comment(lib, "dwmapi.lib")

LPCWSTR CLASS_NAME = L"Win32APP";
#define  BORDER_WIDTH  5

enum Style : DWORD {
    BorderLess = ( WS_THICKFRAME | WS_CAPTION | WS_SYSMENU | WS_MAXIMIZEBOX | WS_MINIMIZEBOX)
};



const std::wstring& Window::registerWindow() {

    static const std::wstring WINDOW_CLASS = []{
        WNDCLASSEX wcx{};
        wcx.cbSize = sizeof(wcx);
        wcx.style = CS_HREDRAW | CS_VREDRAW;
        wcx.hInstance = (HINSTANCE)GetModuleHandle(nullptr);
        wcx.lpfnWndProc = &Window::WndProc;
        wcx.lpszClassName = CLASS_NAME;
        wcx.hbrBackground = reinterpret_cast<HBRUSH>(COLOR_WINDOW + 1);
        wcx.hCursor = LoadCursor((HINSTANCE)GetModuleHandle(nullptr), IDC_ARROW);

        const HRESULT result = RegisterClassEx(&wcx);

        if (FAILED(result)) throw std::runtime_error("Faild To Register Window Class");

        return wcx.lpszClassName;
    }();
    return WINDOW_CLASS;
}