meh

#include "Form.hpp"
#include "MouseListener.hpp"
#include <thread>
#include <chrono>

class Form : public BaseForm
{
    private:
        std::function<void(HWND, HDC)> onPaint;
        std::function<LRESULT(HWND, HDC)> onBackgroundErase;

    public:
        Form(const char *Title, DWORD flags, DWORD flagsex, POINT Location, unsigned short Width, unsigned short Height, HWND Parent = NULL);
        LRESULT WinProc(HWND Hwnd, UINT Msg, WPARAM wParam, LPARAM lParam);

        void setBackgroundListener(const std::function<LRESULT(HWND, HDC)>& onBackgroundErase) {this->onBackgroundErase = onBackgroundErase;}
        void setPaintListener(const std::function<void(HWND, HDC)>& onPaint) {this->onPaint = onPaint;}
};

Form::Form(const char *Title, DWORD flags, DWORD flagsex, POINT Location, unsigned short Width, unsigned short Height, HWND Parent)
{
    if (flags == 0)
        flags = WS_OVERLAPPEDWINDOW | WS_TABSTOP;
    BaseForm::Create(flagsex, Title, flags, Location, Width, Height, Parent);
}

LRESULT Form::WinProc(HWND Hwnd, UINT Msg, WPARAM wParam, LPARAM lParam)
{
    if (onBackgroundErase && Msg == WM_ERASEBKGND)
    {
        return onBackgroundErase(Hwnd, (HDC)wParam);
    }

    switch(Msg)
    {
        case WM_PAINT:
        {
            PAINTSTRUCT ps = {0};
            HDC hdc = BeginPaint(Hwnd, &ps);

            if (onPaint)
            {
                onPaint(Hwnd, hdc);
            }

            EndPaint(Hwnd, &ps);
        }
        break;

        case WM_DESTROY:
            PostQuitMessage(0);
            return 0;

        default:
            return DefWindowProc(Hwnd, Msg, wParam, lParam);
    }
    return 0;
}

int main()
{
    Form parent("Parent", 0, 0, {CW_USEDEFAULT, CW_USEDEFAULT}, 500, 500);
    parent.setBackgroundListener([](HWND hwnd, HDC dc) -> LRESULT{
        SetBkColor(dc, RGB(0xFF, 0xFF, 0xFF));
        return true;
    });

    HBITMAP hbmp = (HBITMAP)LoadImage(GetModuleHandle(NULL), "test.bmp", IMAGE_BITMAP, 0, 0, LR_LOADFROMFILE);

    std::thread([&] {
        while(parent.GetHWND() == NULL && !IsWindowVisible(parent.GetHWND()))
        {
            std::this_thread::sleep_for(std::chrono::milliseconds(0));
        }

        Form child("Baby", WS_OVERLAPPEDWINDOW, WS_EX_LAYERED, {CW_USEDEFAULT, CW_USEDEFAULT}, 500, 500, parent.GetHWND());
        SetLayeredWindowAttributes(child.GetHWND(), RGB(0x80, 0x00, 0xFF), 0, LWA_COLORKEY);

        child.setPaintListener([&](HWND hwnd, HDC dc) {
            BITMAP bitmap;
            HDC hdcMem = CreateCompatibleDC(dc);
            HGDIOBJ old = SelectObject(hdcMem, hbmp);

            GetObject(hbmp, sizeof(bitmap), &bitmap);
            BitBlt(dc, 150, 100, bitmap.bmWidth, bitmap.bmHeight, hdcMem, 0, 0, SRCCOPY);
            SelectObject(hdcMem, old);
            DeleteDC(hdcMem);
        });

        child.Show();
    }).detach();

    int res = parent.Show();
    DeleteObject(hbmp);
    return res;
}