A window transparent overlay stops working after a few seconds

I'm trying to create a transparent overlay over some process' window (I want to draw some stuff on the overlay using Direct3D 9).

The overlay is being created by using an external program (not a .dll injected library or something).

The problem is when I launch the program, an invisible overlay appears over the process window (and it even draws some text on it, so the WM_PAINT seems to be working), but in the next few seconds the cursor becomes a "sand clock" styled (sorry, I don't know how else is it called xd) and if I click on the window, it shows an error "The app is not responding" and becomes solid white.

I import the overlay class into the entry point file and here's how I run it in the main function (simplified):

#include <iostream>
#include "memory.hpp"
#include "overlay.hpp"

int main() {
    Memory mem;
    Overlay ol(&mem);
    HANDLE overlay = CreateThread(NULL, NULL, &ol.static_start, (void*)&ol, NULL, NULL);

    while (1) {
        SendMessage(ol.hwnd, WM_PAINT, NULL, NULL);

        Sleep(2);
    }

    return EXIT_SUCCESS;
}

overlay.hpp:

#ifndef OVERLAY_HPP
#define OVERLAY_HPP
#pragma once
 
#include <Windows.h>
#include <d3d9.h>
#include "paint.hpp" // has a class with methods to draw on overlay using d3dx9
#include "memory.hpp" // has a tHWND variable - handle to target window 
#include <iostream>
#include <dwmapi.h>
#pragma comment(lib, "dwmapi.lib")
 
Paint paint;
 
class Overlay {
private:
    WCHAR _title[20] = L"anoverlay"; // overlay window title
    // HINSTANCE hwnd_inst;
    Memory* mem;
    RECT rect; // coordinates of target window
 
    // registers window class
    ATOM _register_сlass() {
        WNDCLASSEX wc;
        ZeroMemory(&wc, sizeof(WNDCLASSEX));
 
        wc.cbSize = sizeof(WNDCLASSEX);
        wc.style = CS_HREDRAW | CS_VREDRAW;
        wc.lpfnWndProc = WndProc;
        wc.cbClsExtra = NULL;
        wc.cbWndExtra = NULL;
        wc.hInstance = reinterpret_cast<HINSTANCE>(GetWindowLongW(mem->tHWND, GWL_HINSTANCE)); // hwnd_inst;
        wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
        wc.hCursor = LoadCursor(nullptr, IDC_ARROW);
        wc.hbrBackground = WHITE_BRUSH;
        wc.lpszMenuName = NULL;
        wc.lpszClassName = _title;
        wc.hIconSm = LoadIcon(NULL, IDI_APPLICATION);;
 
        return RegisterClassEx(&wc);
    }
 
    // initialise overlay instance
    bool _init_instance(int width, int height) {
        hwnd = CreateWindowEx(WS_EX_TOPMOST | WS_EX_TRANSPARENT | WS_EX_LAYERED, _title, _title, WS_POPUP, rect.left, rect.top, width, height, NULL, NULL, NULL, NULL);
        if (!hwnd) return false;
 
        SetLayeredWindowAttributes(hwnd, 0, 1.0f, LWA_ALPHA);
        SetLayeredWindowAttributes(hwnd, 0, RGB(0, 0, 0), LWA_COLORKEY);
 
        MARGINS _margins = { -1, -1, -1, -1 };
        DwmExtendFrameIntoClientArea(hwnd, &_margins);
 
        ShowWindow(hwnd, SW_SHOW);
        return true;
    }
 
public:
    HWND hwnd; // an HWND to the overlay window
 
    Overlay(Memory* mem) {
        this->mem = mem;
        if (!init()) std::cout << "The overlay window was not created" << std::endl;
    }
 
    ~Overlay() {
        DestroyWindow(hwnd);
    }
 
    bool init() {
        if (!mem->tHWND) return false;
        if (!GetWindowRect(mem->tHWND, &rect)) return false;
        _register_сlass();
 
        if (!_init_instance(rect.right - rect.left, rect.bottom - rect.top)) return false;
        paint = Paint(hwnd, mem->tHWND, rect.right - rect.left, rect.bottom - rect.top);
 
        return true;
    }
 
    DWORD APIENTRY start() {
        MSG msg;
 
        while (true) {
            if (PeekMessage(&msg, hwnd, 0, 0, PM_REMOVE)) {
                if (msg.message == WM_QUIT) break;
                TranslateMessage(&msg);
                DispatchMessage(&msg);
 
                GetWindowRect(mem->tHWND, &rect);
                int width = rect.right - rect.left;
                int height = rect.bottom - rect.top;
 
                MoveWindow(hwnd, rect.left, rect.top, width, height, true);
            }
            Sleep(1);
        }
 
        return (int)msg.wParam;
    }
 
    static DWORD WINAPI static_start(void* param) {
        Overlay* ol = (Overlay*)param;
        return ol->start();
    }
 
    static LRESULT CALLBACK WndProc(HWND hwnd, UINT message, WPARAM wParam, LPARAM lParam) {
        switch (message) {
        case WM_PAINT:
            paint.render();
            break;
        case WM_DESTROY:
            PostQuitMessage(0);
            break;
        default:
            return DefWindowProc(hwnd, message, wParam, lParam);
        }
        return 0;
    }
};
#endif

memory.hpp:

#ifndef MEMORY_HPP
#define MEMORY_HPP
 
#pragma once
#pragma warning(disable: 6276)
 
#include <Windows.h>
#include <TlHelp32.h>
 
const wchar_t* TARGET = L"Telegram.exe"; // you may put any program here, like Notepad or Calculator
LPCSTR WINDOW_NAME = "Telegram";
 
class Memory {
public:
    DWORD tPID;
    HANDLE tProcess;
    HWND tHWND;
 
    Memory() {
        this->tPID = NULL;
        this->tProcess = NULL;
 
        if (!this->handle_process(TARGET)) return;
        this->tHWND = FindWindowA(0, WINDOW_NAME);
    }
 
    ~Memory() {
        CloseHandle(tProcess);
    }
 
    HANDLE handle_process(const wchar_t* processName) {
        HANDLE handle = CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, NULL);
        PROCESSENTRY32 entry;
        entry.dwSize = sizeof(entry);
 
        do {
            if (!wcscmp(entry.szExeFile, processName)) {
                tPID = entry.th32ProcessID;
                CloseHandle(handle);
                tProcess = OpenProcess(PROCESS_ALL_ACCESS, false, tPID);
                return tProcess;
            }
        } while (Process32Next(handle, &entry));
        CloseHandle(handle);
        return NULL;
    }
};
#endif

paint.hpp:

#ifndef PAINT_HPP
#define PAINT_HPP
#pragma once
#pragma warning(disable: 26495)
 
#include <Windows.h>
 
#include <d3d9.h>
#include <d3dx9.h> // Project -> [project name] Properties -> VC++ Directories: Add $(DXSDK_DIR)Include into Include Directories and $(DXSDK_DIR)Lib\x86 into Library directories
// Make sure you have Direct3D 9 SDK installed - https://www.microsoft.com/en-gb/download/details.aspx?id=6812
#pragma comment(lib, "d3d9.lib")
#pragma comment(lib, "d3dx9.lib")
#pragma comment(lib, "legacy_stdio_definitions.lib")
 
class Paint {
private:
    IDirect3D9Ex* object = NULL; // used to create device
    IDirect3DDevice9Ex* device = NULL; // contains functions like begin and end scene 
    D3DPRESENT_PARAMETERS params;
    ID3DXFont* d3d_font = 0; // font used when displaying text
 
    HWND t_hwnd; // target process window
    int width; // target process width
    int height;
 
    int d3d9init(HWND hwnd) {
        if (FAILED(Direct3DCreate9Ex(D3D_SDK_VERSION, &object))) {
            DestroyWindow(hwnd);
        }
 
        ZeroMemory(&params, sizeof(params));
        params.BackBufferWidth = width;
        params.BackBufferHeight = height;
        params.Windowed = TRUE;
        params.SwapEffect = D3DSWAPEFFECT_DISCARD;
        params.hDeviceWindow = hwnd;
        params.MultiSampleQuality = D3DMULTISAMPLE_NONE;
        params.BackBufferFormat = D3DFMT_A8R8G8B8;
        params.EnableAutoDepthStencil = TRUE;
        params.AutoDepthStencilFormat = D3DFMT_D16;
 
        HRESULT res = object->CreateDeviceEx(D3DADAPTER_DEFAULT, D3DDEVTYPE_HAL, hwnd, D3DCREATE_HARDWARE_VERTEXPROCESSING, &params, 0, &device);
        if (FAILED(res)) DestroyWindow(hwnd);
 
        D3DXCreateFont(device, 50, 0, FW_BOLD, 1, false, DEFAULT_CHARSET, OUT_DEVICE_PRECIS, ANTIALIASED_QUALITY, DEFAULT_PITCH, L"Consolas", &d3d_font);
 
        return 0;
    }
 
    void draw_text(char* text, int x, int y, int a, int r, int g, int b) {
        RECT rect;
        rect.left = x;
        rect.top = y;
        d3d_font->DrawTextA(0, text, strlen(text), &rect, DT_NOCLIP, D3DCOLOR_ARGB(a, r, g, b));
    }
 
public:
    Paint() {
        this->device = nullptr;
        this->object = nullptr;
    }
 
    ~Paint() {
        if (object != NULL) object->Release();
        if (device != NULL) device->Release();
    }
 
    Paint(HWND hwnd, HWND t_hwnd, int width, int height) {
        this->t_hwnd = t_hwnd;
        this->width = width;
        this->height = height;
        d3d9init(hwnd);
    }
 
    int render() {
        if (device == nullptr) return 1;
 
        device->Clear(0, 0, D3DCLEAR_TARGET, 0, 1.0f, 0);
        device->BeginScene();
 
        if (t_hwnd == GetForegroundWindow()) {
            draw_text((char*)"Test message", 15, 15, 255, 150, 150, 150);
        }
 
        device->EndScene();
        device->PresentEx(0, 0, 0, 0, 0);
 
        return 0;
    }
};
 
#endif

It just does not work correctly. Any ideas, what am I doing wrong?
Also I've noticed a strange thing, that when I try to debug, it gives me an error "0xC0000005: Access violation reading location 0xADE50000" at the point where I call the RegisterClassEx (overlay.hpp) function. So strange, even though I initialised all the members of the WNDCLASSEX structure. Also it's quite strange that the project builds successfully and I can run the builded .exe file.

The reason for the access conflict is the setting of the hInstance parameter in your WNDCLASSEX structure. You can set it to GetModuleHandle(NULL);

Just like the code :

wc.hInstance = GetModuleHandle(NULL);

The reason why the application is not responding is that you set the GUI thread in the thread, and set the wireless loop in the main thread, which will cause the UI thread to not respond. You can refer to this thread.

You just need to call the start function in the main thread, and then create a thread to execute the SendMessage function can solve this problem:

void fun(const Overlay&ol)
{
    while (1) {
        SendMessage(ol.hwnd, WM_PAINT, NULL, NULL);
    }
}

int main() {
    Memory mem;
    Overlay ol(&mem);
    std::thread t(fun, ol);
    ol.static_start(&ol);
    //HANDLE overlay = CreateThread(NULL, NULL, &ol.static_start, (void*)&ol, NULL, NULL);
    

    t.join();
    return EXIT_SUCCESS;
}

Edit

As @David said, You should not send the WM_PAINT message, just call the start function directly to work properly.