A janky OBS Lua script to display a pop-up notification using GDI when a replay is saved

display_notification.lua

local obs = obslua
local ffi = require("ffi")
local bit = require("bit")

-- Import the necessary libraries for graphics
local gdi32 = ffi.load("gdi32")
local kernel32 = ffi.load("kernel32")
local user32 = ffi.load("user32")

-- Define the necessary Windows API types and functions
ffi.cdef[[
    typedef void* HWND;
    typedef void* HDC;
    typedef void* HGDIOBJ;
    typedef HGDIOBJ HFONT;
    typedef HGDIOBJ HBRUSH;
    typedef HGDIOBJ HPEN;
    typedef unsigned long DWORD;
    typedef int BOOL;
    typedef unsigned char BYTE;
    typedef const char* LPCSTR;
    typedef unsigned int UINT;
    typedef unsigned long ULONG_PTR;
    typedef ULONG_PTR UINT_PTR;
    typedef ULONG_PTR WPARAM;
    typedef long LPARAM;
    typedef unsigned long COLORREF;
    typedef struct {
        long left;
        long top;
        long right;
        long bottom;
    } RECT;

    HDC GetDC(HWND hWnd);
    int ReleaseDC(HWND hWnd, HDC hDC);
    HWND GetDesktopWindow();
    HFONT CreateFontA(int cHeight, int cWidth, int cEscapement, int cOrientation, int cWeight, DWORD bItalic,
                      DWORD bUnderline, DWORD bStrikeOut, DWORD iCharSet, DWORD iOutPrecision, DWORD iClipPrecision,
                      DWORD iQuality, DWORD iPitchAndFamily, LPCSTR pszFaceName);
    HFONT SelectObject(HDC hdc, HFONT hfont);
    int SetBkMode(HDC hdc, int mode);
    BOOL DeleteObject(HFONT hFont);
    BOOL GetClientRect(HWND hWnd, RECT* lpRect);
    int DrawTextA(HDC hdc, LPCSTR lpchText, int cchText, RECT* lprc, UINT format);
    HBRUSH CreateSolidBrush(DWORD color);
    int FillRect(HDC hdc, const RECT *lprc, HBRUSH hbr);
    BOOL SetLayeredWindowAttributes(HWND hwnd, DWORD crKey, BYTE bAlpha, DWORD dwFlags);
    HWND CreateWindowExA(DWORD dwExStyle, LPCSTR lpClassName, LPCSTR lpWindowName, DWORD dwStyle,
                         int X, int Y, int nWidth, int nHeight, HWND hWndParent, void* hMenu, void* hInstance, void* lpParam);
    BOOL ShowWindow(HWND hWnd, int nCmdShow);
    BOOL UpdateWindow(HWND hWnd);
    BOOL DestroyWindow(HWND hWnd);
    UINT_PTR SetTimer(HWND hWnd, UINT_PTR nIDEvent, UINT uElapse, void* lpTimerFunc);
    BOOL KillTimer(HWND hWnd, UINT_PTR uIDEvent);
    int GetSystemMetrics(int nIndex);
    BOOL SetWindowPos(HWND hWnd, HWND hWndInsertAfter, int X, int Y, int cx, int cy, UINT uFlags);
    DWORD GetLastError();
    DWORD FormatMessageA(DWORD dwFlags, const void* lpSource, DWORD dwMessageId, DWORD dwLanguageId, char* lpBuffer, DWORD nSize, va_list* Arguments);
    BOOL PostMessageA(HWND hWnd, UINT Msg, WPARAM wParam, LPARAM lParam);    
    COLORREF SetTextColor(HDC hdc, COLORREF color);
    HPEN CreatePen(int iStyle, int cWidth, COLORREF color);
    BOOL MoveToEx(HDC hdc, int x, int y, void* lpPoint);
    BOOL LineTo(HDC hdc, int x, int y);
]]

-- Constants for FormatMessage
local FORMAT_MESSAGE_FROM_SYSTEM = 0x00001000
local FORMAT_MESSAGE_IGNORE_INSERTS = 0x00000200

-- Constants for window styles
local WS_EX_LAYERED = 0x00080000
local WS_EX_TOPMOST = 0x00000008
local WS_POPUP = 0x80000000
local WS_VISIBLE = 0x10000000
local SWP_NOMOVE = 0x0002
local SWP_NOSIZE = 0x0001
local SWP_SHOWWINDOW = 0x0040
local WM_CLOSE = 0x0010

-- Global variables
local popup_window = nil

-- Function to create and show the pop-up overlay
function show_popup(title, message)
    local screen_width = ffi.C.GetSystemMetrics(0)  -- SM_CXSCREEN
    local screen_height = ffi.C.GetSystemMetrics(1)  -- SM_CYSCREEN
    local popup_width = 350
    local popup_height = 120
    local x = screen_width - popup_width - 20
    local y = 20  -- Position at the top

    -- Create a layered window for transparency
    popup_window = ffi.C.CreateWindowExA(
        bit.bor(WS_EX_LAYERED, WS_EX_TOPMOST),
        "Static",
        "",
        bit.bor(WS_POPUP, WS_VISIBLE),
        x, y, popup_width, popup_height,
        nil, nil, nil, nil
    )

    -- Set window transparency
    ffi.C.SetLayeredWindowAttributes(popup_window, 0, 230, 2)  -- Increased opacity

    -- Show and update the window
    ffi.C.ShowWindow(popup_window, 1)
    ffi.C.UpdateWindow(popup_window)

    -- Ensure the window stays on top
    ffi.C.SetWindowPos(popup_window, ffi.cast("HWND", -1), 0, 0, 0, 0, 
        bit.bor(SWP_NOMOVE, SWP_NOSIZE, SWP_SHOWWINDOW))

    -- Get the device context
    local hdc = ffi.C.GetDC(popup_window)

    -- Create and select the fonts
    local hFontTitle = ffi.C.CreateFontA(20, 0, 0, 0, 700, 0, 0, 0, 0, 0, 0, 0, 0, "Segoe UI")
    local hFontMessage = ffi.C.CreateFontA(16, 0, 0, 0, 400, 0, 0, 0, 0, 0, 0, 0, 0, "Segoe UI")

    -- Set transparent background
    ffi.C.SetBkMode(hdc, 1)

    -- Create and fill rectangle with semi-transparent background
    local rect = ffi.new("RECT", {0, 0, popup_width, popup_height})
    local hBrush = ffi.C.CreateSolidBrush(0x00303030)  -- Dark gray background
    ffi.C.FillRect(hdc, rect, hBrush)

    -- Draw title
    ffi.C.SelectObject(hdc, hFontTitle)
    ffi.C.SetTextColor(hdc, 0x00FFFFFF)  -- White text
    rect.top = 10
    rect.left = 15
    ffi.C.DrawTextA(hdc, title, #title, rect, 0x00000000)

    -- Draw message
    ffi.C.SelectObject(hdc, hFontMessage)
    ffi.C.SetTextColor(hdc, 0x00E0E0E0)  -- Light gray text
    rect.top = 45
    rect.left = 15
    ffi.C.DrawTextA(hdc, message, #message, rect, 0x00000000)

    -- Draw a subtle border
    local hPen = ffi.C.CreatePen(0, 1, 0x00505050)  -- Slightly lighter gray
    local oldPen = ffi.C.SelectObject(hdc, hPen)
    ffi.C.MoveToEx(hdc, 0, 0, nil)
    ffi.C.LineTo(hdc, popup_width - 1, 0)
    ffi.C.LineTo(hdc, popup_width - 1, popup_height - 1)
    ffi.C.LineTo(hdc, 0, popup_height - 1)
    ffi.C.LineTo(hdc, 0, 0)

    -- Clean up
    ffi.C.SelectObject(hdc, oldPen)
    ffi.C.DeleteObject(hFontTitle)
    ffi.C.DeleteObject(hFontMessage)
    ffi.C.DeleteObject(hBrush)
    ffi.C.DeleteObject(hPen)
    ffi.C.ReleaseDC(popup_window, hdc)

    -- Set a timer to close the popup after 2 seconds
    obs.timer_add(on_timer, 2000)
end


-- Function to handle OBS events
function on_event(event)
    if event == obs.OBS_FRONTEND_EVENT_REPLAY_BUFFER_SAVED then
        print("Replay saved")
        show_popup("Replay Saved", "Your replay has been successfully saved.")
    end
end

-- Function to get the last error message
local function get_last_error_message()
    local error_code = ffi.C.GetLastError()
    local buffer = ffi.new("char[?]", 256)
    local size = ffi.C.FormatMessageA(
        bit.bor(FORMAT_MESSAGE_FROM_SYSTEM, FORMAT_MESSAGE_IGNORE_INSERTS),
        nil,
        error_code,
        0,
        buffer,
        256,
        nil
    )
    if size == 0 then
        return "Unknown error"
    else
        return ffi.string(buffer, size)
    end
end

-- Function to handle the timer event
function on_timer()
    print("Timer triggered, closing popup")
    if popup_window ~= nil then
        -- Post a WM_CLOSE message to the window
        local result = ffi.C.PostMessageA(popup_window, WM_CLOSE, 0, 0)
        if result == 0 then
            local error_message = get_last_error_message()
            print("Failed to post WM_CLOSE message: " .. error_message)
        else
            print("WM_CLOSE message posted successfully")
        end
        popup_window = nil
    end
    obs.timer_remove(on_timer)
end

-- Script load function
function script_load(settings)
    obs.obs_frontend_add_event_callback(on_event)
end

-- Script unload function
function script_unload()
    obs.obs_frontend_remove_event_callback(on_event)
    if popup_window ~= nil then
        ffi.C.DestroyWindow(popup_window)
    end
end