RGM (Ralefaso GlassMirror)

A zero-configuration screen extender with automatic network discovery

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Overview

RGM (Ralefaso GlassMirror) is a lightweight, cross-platform screen extender that turns any networked machine into a wireless second monitor. It implements SSDP (Simple Service Discovery Protocol) to automatically detect receiver hosts on your local network, requiring zero manual IP configuration.

The receiver machine opens a borderless fullscreen window that presents itself as a natural display extension — positioned logically to the right of, or below, the sender's screen. The result looks and behaves like a real second monitor plugged into the sender machine.

A mirror mode (classic screen duplication) is also available for presentations and demos.

Features

Category	Capability
Screen Extension	Extend Right, Extend Below, or Mirror modes — chosen per session
Discovery	Zero-configuration SSDP automatic detection, no IP setup needed
Performance	60 FPS streaming, 4 MB socket buffers, TCP_NODELAY optimisation
CPU Offload	RLE frame compression and colour correction offloaded to the receiver's CPU (TCP 8082)
Port Inspector	Full remote port inspection: list, query, and kill processes on any receiver port (TCP 8083)
Platform Support	Linux (X11), Windows 10/11, macOS 10.15+
Display Handling	Auto-resolution handshake, borderless fullscreen, aspect-ratio scaling
Splash Screen	rcorp.jpeg corporate logo displayed at launch via SDL2_image
Monitoring	Real-time FPS, bandwidth, source/destination resolution, real measured offload timing
User Interface	Splash screen, menu-driven launcher, direct executable mode

Architecture

Component Structure

RGM/
├── makefile                     # Cross-platform build (Linux/macOS/Windows)
├── src/                         # Source code
│   ├── app.cpp                  # Launcher: splash + menu
│   ├── sender.cpp               # Screen capture, extender handshake, stream, port inspector client
│   ├── receiver.cpp             # Fullscreen display, SSDP advertiser, compute svc, port svc
│   ├── discover.cpp             # SSDP discovery engine
│   ├── discover.h               # Discovery API
│   ├── gpu_accelerate.c         # Remote CPU offload (RLE compress / colorfix) with real timing
│   ├── gpu_accelerate.h         # Compute offload API
│   ├── ports.cpp                # Remote port inspection service (server + client)
│   └── ports.h                  # Port inspector API
├── assets/
│   └── icons/
│       ├── rcorp.jpeg           # Corporate splash logo  ← shown at startup
│       └── RGM.png              # Fallback splash logo
├── build/                       # Compiled object files
├── sender                       # Sender executable
├── receiver                     # Receiver executable
├── app                          # Launcher executable
└── readme.md

Executables

Executable	Role
`app`	Menu launcher — choose send / receive mode
`sender`	Captures local display, negotiates mode, streams frames, runs port inspector client
`receiver`	Advertises via SSDP, opens fullscreen window, renders frames, runs compute and port services

Network Ports

Port	Protocol	Purpose
1900	UDP multicast	SSDP discovery (M-SEARCH / NOTIFY)
8081	TCP	Video frame stream
8082	TCP	CPU compute offload service (RLE compress / colour fix)
8083	TCP	Remote port inspection service

How It Works

1 — Discovery (SSDP)

RGM uses the same multicast discovery protocol as UPnP/DLNA — no manual IP entry required.

Receiver  →  joins 239.255.255.250:1900
           →  sends periodic NOTIFY announcements
           →  listens for M-SEARCH queries

Sender    →  broadcasts M-SEARCH to 239.255.255.250:1900
           →  collects 200 OK responses
           →  lists discovered receivers
           →  user picks one

2 — Extended Handshake

Once the user selects a receiver and a display mode, the sender opens a TCP connection to port 8081 and exchanges an extended handshake:

Sender → Receiver   (16 bytes, network byte order)
  uint32  sender_width
  uint32  sender_height
  uint32  fps
  uint32  mode          0=mirror  1=extend-right  2=extend-below

Receiver → Sender   (12 bytes, network byte order)
  uint32  receiver_width
  uint32  receiver_height
  uint32  status        0=OK

The sender uses the receiver's reported resolution to display the combined virtual desktop layout in the terminal.

3 — Display Window Strategy

Mode	Window behaviour
Extend Right / Below	`SDL_WINDOW_FULLSCREEN_DESKTOP` — borderless, covers the entire receiver display, appears as a physical second monitor
Mirror	Normal resizable window, scaled to fit

In extend modes the receiver also draws a subtle 2-pixel blue edge glow on the side that logically joins to the sender's screen (left edge for extend-right, top edge for extend-below).

4 — Frame Stream

Every frame:

Sender  →  captures screen (X11 / GDI / CoreGraphics)
        →  optionally RLE-compresses via compute offload service
        →  sends  [uint32 frame_size] [frame_bytes]

Receiver →  reads size header
         →  reads frame_bytes
         →  RLE-decompresses if frame_size < raw_size
         →  SDL_UpdateTexture → SDL_RenderCopy → SDL_RenderPresent

5 — CPU Compute Offload Service (port 8082)

The receiver runs a second TCP server on port 8082 (gpu_accelerate.c). The sender connects to it optionally before streaming begins. All work is performed on the receiver's CPU — the sender sends raw pixel data, the receiver processes it and sends back the result, so processing load is shifted off the sender machine.

Timing is measured with clock_gettime(CLOCK_MONOTONIC) on Linux/macOS and QueryPerformanceCounter on Windows, so the ms_elapsed values reported are real measured durations, not estimates.

Operation	Code	Description
PING	0xFF	Heartbeat / handshake check
COMPRESS	0x01	RLE-compress a raw RGB frame (receiver CPU)
COLORCONV	0x03	BGR → RGB channel swap (receiver CPU)

If the compute service is unavailable the sender falls back silently to uncompressed local frames.

6 — Port Inspection Service (port 8083)

The receiver runs a third TCP server on port 8083 (ports.cpp). Once connected, the sender can interactively inspect every listening socket on the receiver machine:

Operation	Description
LIST_TCP	All TCP sockets with PID, process name, state, addresses
LIST_UDP	All UDP sockets
LIST_ALL	TCP + UDP combined
GET_PORT	Details for one specific port number
KILL_PORT	Send SIGTERM to the process owning a port

Port data is collected natively per platform:

Platform	Method
Linux	`/proc/net/tcp`, `tcp6`, `udp`, `udp6` + inode→PID mapping via `/proc/PID/fd`
macOS	`lsof -nP -iTCP -iUDP`
Windows	`GetExtendedTcpTable` / `GetExtendedUdpTable` (iphlpapi) + `CreateToolhelp32Snapshot`

Streaming Architecture

┌─────────────┐   handshake   ┌──────────────────────────────────────────┐
│   SENDER    │  ──────────►  │              RECEIVER                    │
│             │               │                                          │
│ capture     │  frame data   │  RLE decode → SDL2 texture               │
│ (X11/GDI/  │  ──────────►  │  → fullscreen borderless window          │
│  CG)        │  TCP 8081     │    (extend-right / below / mirror)       │
│             │               │                                          │
│ RLE via     │  compute proto│  gpu_service_run() on TCP 8082           │
│ CPU offload │  ──────────►  │  (RLE compress / color fix, real timing) │
│             │  TCP 8082     │                                          │
│ port cmds   │  port proto   │  ports_service_run() on TCP 8083         │
│ interactive │  ──────────►  │  (list/query/kill receiver ports)        │
└─────────────┘  TCP 8083     └──────────────────────────────────────────┘

Display Modes

Extend Right (default)

The receiver's display appears logically to the right of the sender's screen. The receiver opens a borderless fullscreen window with a blue left-edge indicator showing where the screens join.

┌────────────────┬────────────────┐
│                │                │
│  SENDER        │  RECEIVER      │
│  (your machine)│  (extended)    │
│                │◄ blue edge     │
└────────────────┴────────────────┘

Extend Below

The receiver's display appears below the sender's screen, with a blue top-edge indicator.

┌────────────────────────────────┐
│         SENDER                 │
└────────────────────────────────┘
  ▲ blue edge
┌────────────────────────────────┐
│         RECEIVER               │
└────────────────────────────────┘

Mirror

The receiver displays an exact duplicate of the sender's screen in a normal resizable window. Use this for presentations.

System Requirements

Hardware

Component	Minimum	Recommended
CPU	1 GHz	2 GHz dual-core
RAM	256 MB	512 MB
Network	100 Mbps	1 Gbps wired
Display	800×600	1920×1080

Software by Platform

Linux

Requirement	Detail
Distribution	Ubuntu 18.04+, Debian 10+, Fedora 32+, Arch
Compiler	GCC 8+ (C++17)
Libraries	libX11-dev, libsdl2-dev, libsdl2-image-dev, pthread
Build tool	make

Windows

Requirement	Detail
Version	Windows 10 build 1903+ or Windows 11
Compiler	MinGW-w64 (MSYS2) or MSVC 2019+
Libraries	SDL2, SDL2_image (from MSYS2 packages)
SDK	Windows SDK 10.0+ (iphlpapi required for port inspector)

macOS

Requirement	Detail
Version	macOS Catalina 10.15+
Compiler	Clang 12+ (Xcode 12+)
Libraries	`brew install sdl2 sdl2_image`
Screen capture	CoreGraphics (built-in)

Note: SDL2_image is required on all platforms for the rcorp.jpeg splash screen.

Installation

Linux (Ubuntu / Debian)

git clone https://github.com/RR-Ralefaso/RGM.git
cd RGM
sudo apt update
sudo apt install -y g++ make libx11-dev libsdl2-dev libsdl2-image-dev
make install-deps
make
./app

Linux (Fedora / RHEL)

sudo dnf install gcc-c++ make libX11-devel SDL2-devel SDL2_image-devel
git clone https://github.com/RR-Ralefaso/RGM.git
cd RGM && make && ./app

Linux (Arch)

sudo pacman -S gcc make libx11 sdl2 sdl2_image
git clone https://github.com/RR-Ralefaso/RGM.git
cd RGM && make install-deps && make && ./app

macOS

# Install Homebrew if needed
/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

brew install sdl2 sdl2_image
git clone https://github.com/RR-Ralefaso/RGM.git
cd RGM && make install-deps && make && ./app

Windows (MSYS2 / MinGW)

# In MSYS2 MinGW64 shell
pacman -S mingw-w64-x86_64-SDL2 mingw-w64-x86_64-SDL2_image

git clone https://github.com/RR-Ralefaso/RGM.git
cd RGM
make install-deps
make
./app.exe

Building from Source

Build Commands

Command	Description
`make`	Build all components
`make sender`	Build sender only
`make receiver`	Build receiver only
`make app`	Build launcher only
`make debug`	Build with `-g -O0 -DDEBUG`
`make clean`	Remove all build output
`make check`	Verify environment, sources, and assets
`make install-deps`	Install system dependencies

Build Output

RGM/
├── sender      (or sender.exe)
├── receiver    (or receiver.exe)
├── app         (or app.exe)
└── build/
    ├── sender.o
    ├── receiver.o
    ├── app.o
    ├── discover.o
    ├── gpu_accelerate.o
    └── ports.o

Usage Guide

Quick Start

On the receiver machine (the machine that will act as the second monitor):

./receiver

Expected output:

========================================
  RGM RECEIVER v2.0.1
========================================
  Local IP   : 192.168.1.105
  My display : 1920x1080
  Stream TCP : 8081
  Compute TCP: 8082
  Ports TCP  : 8083
  SSDP UDP   : 239.255.255.250:1900
  GPU Stats  : gpu_stats.json
  Modes      : extend-right | extend-below | mirror
========================================
Waiting for sender on TCP 8081 ...

On the sender machine (the machine whose screen you want to extend):

./sender

Interactive session:

Discovering receivers...
  Found: 192.168.1.105:8081 – testing...
  Connection OK
Discovery complete: 1 receiver(s) found

RECEIVERS FOUND:
  [0] 192.168.1.105:8081

  Select display mode:
  1  Extend Right  (receiver = right monitor)
  2  Extend Below  (receiver = bottom monitor)
  3  Mirror        (duplicate screen)
  Choice [1]:

Mode: Extend Right

Remote compute (CPU offload) active
Port inspector active  (press 'p' during stream)

Extended desktop active:
  Sender:   1920x1080
  Receiver: 1920x1080
  Layout:   Extend Right
  Total:    3840x1080

Streaming – Ctrl+C to stop

The receiver's display immediately goes fullscreen and begins showing the sender's screen content.

Using the Launcher

./app

The launcher shows the rcorp.jpeg splash screen then presents:

╔════════════════════════════════╗
║      RGM v2.0.2                ║
╠════════════════════════════════╣
║                                ║
║  1.  SEND SCREEN               ║
║  2.  RECEIVE SCREEN            ║
║  0.  EXIT                      ║
║                                ║
╚════════════════════════════════╝

Receiver Controls

Key	Action
ESC or Q	Disconnect and exit
F11	Toggle fullscreen (extend modes)
Close window	Stop receiving

Sender Controls

Key / Input	Action
Ctrl+C	Graceful shutdown
Number at prompt	Select receiver from list
1 / 2 / 3 at mode prompt	Choose Extend Right / Extend Below / Mirror
`p` at stream prompt	Open Port Inspector menu

Port Inspector Menu

When the sender connects to a receiver, it also connects to the port inspection service on TCP 8083. Press p (or enter it at the prompt) to open the interactive menu:

╔════════════════════════════════╗
║   RECEIVER PORT INSPECTOR      ║
╠════════════════════════════════╣
║  1. List all TCP ports         ║
║  2. List all UDP ports         ║
║  3. List ALL ports             ║
║  4. Query specific port        ║
║  5. Kill process on port       ║
║  0. Back to stream             ║
╚════════════════════════════════╝

The table output shows protocol, local address:port, remote address:port, TCP state, PID, and process name — all read live from the receiver OS. The kill option sends SIGTERM (Linux/macOS) or TerminateProcess (Windows) to the process owning the specified port.

Network Configuration

Firewall Rules

Linux (UFW)

sudo ufw allow 1900/udp comment 'RGM SSDP'
sudo ufw allow 8081/tcp comment 'RGM Video Stream'
sudo ufw allow 8082/tcp comment 'RGM Compute Offload'
sudo ufw allow 8083/tcp comment 'RGM Port Inspector'
sudo ufw reload

Linux (iptables)

sudo iptables -A INPUT -p udp --dport 1900 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 8081 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 8082 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 8083 -j ACCEPT

Windows (PowerShell — Administrator)

New-NetFirewallRule -DisplayName "RGM SSDP"     -Direction Inbound -Protocol UDP -LocalPort 1900 -Action Allow
New-NetFirewallRule -DisplayName "RGM Stream"   -Direction Inbound -Protocol TCP -LocalPort 8081 -Action Allow
New-NetFirewallRule -DisplayName "RGM Compute"  -Direction Inbound -Protocol TCP -LocalPort 8082 -Action Allow
New-NetFirewallRule -DisplayName "RGM Ports"    -Direction Inbound -Protocol TCP -LocalPort 8083 -Action Allow

macOS

sudo /usr/libexec/ApplicationFirewall/socketfilterfw --add /path/to/receiver
sudo /usr/libexec/ApplicationFirewall/socketfilterfw --add /path/to/sender

Network Requirements

All devices must be on the same subnet
Multicast must be enabled on network switches (IGMP snooping)
Wired Ethernet recommended for 60 FPS at 1080p
WiFi 5 GHz (802.11ac) workable for lower resolutions

Performance Characteristics

Bandwidth (uncompressed RGB24)

Resolution	30 FPS	60 FPS
1280×720	~125 MB/s	~250 MB/s
1920×1080	~280 MB/s	~560 MB/s
2560×1440	~500 MB/s	~1 GB/s

CPU offload RLE compression typically reduces bandwidth by 30–70% for desktop content (text, UI). Video content compresses less. The compression ratio and time are reported accurately based on real measurements.

Latency

Connection	Typical Latency
Wired 1 Gbps	< 5 ms
WiFi 5 GHz	10–15 ms
WiFi 2.4 GHz	20–35 ms

Compute Offload Stats

The receiver writes live statistics to gpu_stats.json every 60 seconds and prints a summary to the console every 30 seconds. Stats include total operations, bytes processed in/out, real average compression ratio, actual milliseconds per operation, and per-client connection counts.

Troubleshooting

Problem	Check	Solution
No receivers found	Network connectivity	Verify firewall allows UDP 1900 on receiver
Connection refused	Receiver running?	Check port 8081 is open; restart receiver
Black screen on receiver	Handshake exchange	Ensure both binaries are the same version
Low FPS	Network utilisation	Use wired Ethernet; enable CPU offload
Compute offload unavailable	Port 8082 blocked	Allow TCP 8082 in firewall on receiver
Port inspector unavailable	Port 8083 blocked	Allow TCP 8083 in firewall on receiver
rcorp.jpeg not showing	Asset path	Place `rcorp.jpeg` in `assets/icons/`; run `make check`
SDL_image not found	Missing library	Run `make install-deps` or install `libsdl2-image-dev`
Build fails on Windows	Missing iphlpapi	Ensure Windows SDK is installed; iphlpapi is linked automatically
Build fails on macOS	Homebrew paths	Run `brew install sdl2 sdl2_image`; check `BREW_PREFIX` in makefile

Diagnostic Commands

# Verify receiver is listening on all four ports
netstat -tulpn | grep -E '8081|8082|8083|1900'

# Test TCP reachability
nc -zv <receiver-ip> 8081
nc -zv <receiver-ip> 8082
nc -zv <receiver-ip> 8083

#ensure all dependancies are installed 
make install-deps

# Check assets and source files
make check

# Full rebuild
make clean && make

Roadmap

Support the Project

Action	Impact
Star on GitHub	Increases project visibility
Become a Sponsor	Funds ongoing development
Report Issues	Helps improve stability
Contribute Code	Accelerates feature development

╔════════════════════════════════════════════════════════════════╗
║                                                                ║
║   "Seeking to solve complex business problems through          ║
║    analytical precision and elegant code - on any platform."   ║
║                                                                ║
║                    - RR-Ralefaso (polaris)                     ║
║                                                                ║
╚════════════════════════════════════════════════════════════════╝

Linux • Windows 10/11 • macOS — One codebase, all platforms.

Star on GitHub • Sponsor Development

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RGM (Ralefaso GlassMirror)

Table of Contents

Overview

Features

Architecture

Component Structure

Executables

Network Ports

How It Works

1 — Discovery (SSDP)

2 — Extended Handshake

3 — Display Window Strategy

4 — Frame Stream

5 — CPU Compute Offload Service (port 8082)

6 — Port Inspection Service (port 8083)

Streaming Architecture

Display Modes

Extend Right (default)

Extend Below

Mirror

System Requirements

Hardware

Software by Platform

Linux

Windows

macOS

Installation

Linux (Ubuntu / Debian)

Linux (Fedora / RHEL)

Linux (Arch)

macOS

Windows (MSYS2 / MinGW)

Building from Source

Build Commands

Build Output

Usage Guide

Quick Start

Using the Launcher

Receiver Controls

Sender Controls

Port Inspector Menu

Network Configuration

Firewall Rules

Linux (UFW)

Linux (iptables)

Windows (PowerShell — Administrator)

macOS

Network Requirements

Performance Characteristics

Bandwidth (uncompressed RGB24)

Latency

Compute Offload Stats

Troubleshooting

Diagnostic Commands

Roadmap

Support the Project

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