Protocol Overview

QLC+ supports a wide range of lighting control protocols through its plugin architecture. Each protocol is implemented as a plugin that handles input, output, or both directions of communication.

Plugin Architecture

All I/O plugins implement the QLCIOPlugin interface:

class QLCIOPlugin : public QObject {
    virtual void init() = 0;
    virtual QString name() const = 0;
    virtual int capabilities() const = 0;
    virtual QString pluginInfo() const = 0;
};

Plugin Capabilities

Plugins declare their capabilities as a bitmask:

enum Capability {
    Output      = 1 << 0,  // DMX output
    Input       = 1 << 1,  // Input from controllers
    Feedback    = 1 << 2,  // Visual feedback to devices
    Infinite    = 1 << 3,  // Unlimited universes
    RDM         = 1 << 4,  // Remote Device Management
    Beats       = 1 << 5   // Beat generation
};

A single plugin can support multiple capabilities. For example, Art-Net supports both input and output.

Network Protocols

Art-Net

Protocol: Art-Net (DMX over Ethernet) Plugin: artnet Capabilities: Output, Input, Infinite

class ArtNetPlugin : public QLCIOPlugin {
    // Supports multiple universes over Ethernet
    // Standard Art-Net port: 6454 (UDP)
};

Key Features:

Industry-standard DMX over Ethernet protocol
Supports up to 32,768 universes (Art-Net 4)
Broadcast and unicast transmission modes
Auto-discovery of Art-Net nodes
Configurable universe mapping

Configuration Parameters:

inputUni - Input universe number
outputIP - Target IP address for output
outputUni - Output universe number
transmitMode - Broadcast or unicast mode

Use Cases

Multi-universe installations
Distributed lighting systems
Networked lighting control
Integration with professional consoles

Network Requirements

Gigabit Ethernet recommended
Low-latency network switches
Proper VLAN configuration
Multicast support (for broadcast mode)

sACN (E1.31)

Protocol: Streaming ACN (ANSI E1.31) Plugin: E1.31 Capabilities: Output, Input, Infinite Key Features:

ANSI standard for DMX over IP
Priority-based source selection
Universe discovery protocol
Multicast and unicast modes
Compatible with Art-Net infrastructure

Advantages:

Open standard (no licensing)
Better conflict resolution than Art-Net
Built-in priority handling
Supports up to 63,999 universes

OSC (Open Sound Control)

Protocol: Open Sound Control Plugin: osc Capabilities: Input, Output, Feedback Key Features:

Flexible, extensible protocol
Human-readable addressing
Works with TouchOSC, Lemur, and similar apps
Bidirectional communication
Custom message formats

Example OSC Addresses:

/qlc/fader/1
/qlc/button/scene/1
/qlc/master

OS2L

Protocol: ShowXpress OS2L Plugin: os2l Capabilities: Input, Output Key Features:

ShowXpress and SweetLight protocol
Network-based control
Designed for iOS/Android control

USB/Serial Protocols

DMX USB

Plugin: dmxusb Capabilities: Output, Input, RDM (device-dependent) Supported Devices:

Enttec

Open DMX USB
DMX USB Pro
DMX USB Pro Mk2

Other Manufacturers

DMXKing ultraDMX
Eurolite USB-DMX512
Velleman K8062

class DMXUSBWidget {
    // Base class for DMX USB devices
    virtual bool open() = 0;
    virtual bool close() = 0;
    virtual bool writeUniverse(const QByteArray& data) = 0;
};

Key Features:

Direct USB connection
Low latency
Compact hardware
RDM support (Pro models)
Galvanic isolation (most models)

MIDI

Plugin: midi Capabilities: Input, Output, Feedback, Beats Key Features:

MIDI Note, Control Change, and Program Change
Beat clock generation and synchronization
Support for MIDI show control
Channel routing and filtering
Feedback to LED rings and motorized faders

MIDI Message Types:

Note On/Off - Buttons and triggers
Control Change - Faders and knobs
Program Change - Scene selection
Clock - BPM synchronization

HID (Human Interface Device)

Plugin: hid Capabilities: Input, Feedback Key Features:

Generic USB HID device support
Custom controller support
Joystick and gamepad input
LED feedback for supported devices

DMX Hardware Interfaces

DMX4Linux

Plugin: dmx4linux Capabilities: Output, Input Key Features:

Native Linux DMX driver support
Direct kernel interface
Low-level hardware access
High performance

Peperoni

Plugin: peperoni Capabilities: Output, Input Key Features:

Peperoni Lighting DMX interfaces
Multiple universe support
Windows and Linux support

OLA (Open Lighting Architecture)

Plugin: ola Capabilities: Output, Input, RDM Key Features:

Integration with Open Lighting Architecture
Supports 100+ devices through OLA
RDM device configuration
Plugin-based architecture
Cross-platform compatibility

OLA acts as a middleware layer, allowing QLC+ to access dozens of lighting protocols and devices through a single plugin.

Specialized Protocols

Enttec Wing

Plugin: enttecwing Capabilities: Input Supported Devices:

Enttec Shortcut Wing
Enttec Playback Wing
Enttec Program Wing

Key Features:

Dedicated control surfaces
Motorized faders (Playback Wing)
LED feedback
USB connection

SPI (Serial Peripheral Interface)

Plugin: spi Capabilities: Output Key Features:

Direct control of LED strips
Support for WS2801, APA102, etc.
Raspberry Pi GPIO output
High-speed serial communication

Common Uses:

Pixel mapping
LED strip control
Embedded systems
Low-cost installations

UART (Serial)

Plugin: uart Capabilities: Output Key Features:

Serial port DMX output
Arduino/embedded system integration
Custom protocol support
RS-232/RS-485 interfaces

GPIO

Plugin: gpio Capabilities: Input, Output Key Features:

Raspberry Pi GPIO pins
Direct hardware control
Button and LED interfacing
Custom hardware integration

Plugin Operations

Opening and Closing Lines

Plugins manage input/output lines:

// Output operations
virtual bool openOutput(quint32 output, quint32 universe);
virtual void closeOutput(quint32 output, quint32 universe);
virtual void writeUniverse(quint32 universe, quint32 output, 
                          const QByteArray& data, bool dataChanged);

// Input operations
virtual bool openInput(quint32 input, quint32 universe);
virtual void closeInput(quint32 input, quint32 universe);

Input Value Signal

Plugins emit signals when input values change:

signals:
    void valueChanged(quint32 universe, quint32 input, 
                     quint32 channel, uchar value, 
                     const QString& key = 0);

Feedback

Send visual feedback to input devices:

virtual void sendFeedBack(quint32 universe, quint32 inputLine,
                         quint32 channel, uchar value, 
                         const QVariant& params);

Plugin Parameters

Plugins can accept custom parameters:

virtual void setParameter(quint32 universe, quint32 line, 
                         Capability type,
                         QString name, QVariant value);

virtual void unSetParameter(quint32 universe, quint32 line, 
                           Capability type, QString name);

virtual QMap<QString, QVariant> getParameters(
    quint32 universe, quint32 line, Capability type) const;

Common Parameters:

IP addresses (network plugins)
Universe numbers
Transmission modes
Device-specific settings

RDM Support

Some plugins support RDM (Remote Device Management):

virtual bool sendRDMCommand(quint32 universe, quint32 line, 
                           uchar command, QVariantList params);

signals:
    void rdmValueChanged(quint32 universe, quint32 line, 
                        QVariantMap data);

RDM Capabilities:

Device discovery
Parameter reading and setting
DMX addressing configuration
Device information queries

Protocol Selection Guide

Small Installations

Recommended: DMX USB, Enttec interfacesSimple, reliable, cost-effective for single-universe setups.

Medium Installations

Recommended: Art-Net, sACNMultiple universes, flexible routing, expandable infrastructure.

Large Installations

Recommended: Art-Net, sACN with OLADistributed control, redundancy, professional-grade reliability.

Mobile Setups

Recommended: DMX USB, MIDI controllersPortable, quick setup, minimal infrastructure requirements.

Embedded Systems

Recommended: SPI, GPIO, UARTDirect hardware control, custom integration, low power.

Control Surfaces

Recommended: MIDI, OSC, HIDInteractive control, feedback, touch interfaces.

Best Practices

Network Protocols

Use dedicated network infrastructure for lighting
Configure proper QoS and VLAN settings
Monitor network bandwidth and latency
Use unicast for specific routing needs
Test failover scenarios

USB Protocols

Use quality USB cables (short as possible)
Avoid USB hubs when possible
Check for driver conflicts
Test USB power requirements
Keep firmware updated

Performance

Match protocol to your needs (don’t over-engineer)
Monitor CPU usage with multiple universes
Optimize update rates
Close unused plugin lines
Test worst-case scenarios

Compatibility

Verify protocol versions
Test with actual hardware before deployment
Document plugin configurations
Keep backup configurations
Plan for equipment failures

Configuration Example

Configuring plugins through the Input/Output Map:

// Configure Art-Net output
inputOutputMap->setOutputPatch(
    0,                    // Universe 0
    "Art-Net",           // Plugin name
    "192.168.1.100",    // Network interface
    0                     // Output line
);

// Set Art-Net parameters
OutputPatch* patch = inputOutputMap->outputPatch(0);
patch->setPluginParameter("outputIP", "192.168.1.50");
patch->setPluginParameter("outputUni", 1);
patch->setPluginParameter("transmitMode", "unicast");

// Configure MIDI input
inputOutputMap->setInputPatch(
    0,                    // Universe 0
    "MIDI",              // Plugin name
    "USB MIDI Device",   // Device name
    0,                    // Input line
    "Behringer BCF2000"  // Input profile
);

Troubleshooting

No output on network protocols

Check network connectivity
Verify firewall settings
Confirm universe numbers match
Test with network monitoring tools
Check for IP conflicts

USB device not detected

Verify drivers are installed
Check USB cable and port
Try different USB ports
Check device permissions (Linux)
Restart QLC+ and reconnect device

MIDI not responding

Confirm MIDI routing
Check MIDI channel settings
Verify input profile is correct
Test with MIDI monitor
Check for MIDI conflicts with other software

High latency or dropped frames

Reduce universe count
Optimize network infrastructure
Check CPU usage
Disable unused plugins
Use wired connections instead of wireless

Code References

Plugin Interface: plugins/interfaces/qlcioplugin.h:90
Plugin Cache: engine/src/ioplugincache.h:34
Art-Net Plugin: plugins/artnet/src/artnetplugin.h:47
DMX USB: plugins/dmxusb/src/dmxusb.h

Get Started

Core Concepts

Functions

Fixture Management

Virtual Console

Input/Output

Advanced Features

​Plugin Architecture

​Plugin Capabilities

​Network Protocols

​Art-Net

Use Cases

Network Requirements

​sACN (E1.31)

​OSC (Open Sound Control)

​OS2L

​USB/Serial Protocols

​DMX USB

Enttec

Other Manufacturers

​MIDI

​HID (Human Interface Device)

​DMX Hardware Interfaces

​DMX4Linux

​Peperoni

​OLA (Open Lighting Architecture)

​Specialized Protocols

​Enttec Wing

​SPI (Serial Peripheral Interface)

​UART (Serial)

​GPIO

​Plugin Operations

​Opening and Closing Lines

​Input Value Signal

​Feedback

​Plugin Parameters

​RDM Support

​Protocol Selection Guide

Small Installations

Medium Installations

Large Installations

Mobile Setups

Embedded Systems

Control Surfaces

​Best Practices

​Network Protocols

​USB Protocols

​Performance

​Compatibility

​Configuration Example

​Troubleshooting

​Code References

Plugin Architecture

Plugin Capabilities

Network Protocols

Art-Net

sACN (E1.31)

OSC (Open Sound Control)

OS2L

USB/Serial Protocols

DMX USB

MIDI

HID (Human Interface Device)

DMX Hardware Interfaces

DMX4Linux

Peperoni

OLA (Open Lighting Architecture)

Specialized Protocols

Enttec Wing

SPI (Serial Peripheral Interface)

UART (Serial)

GPIO

Plugin Operations

Opening and Closing Lines

Input Value Signal

Feedback

Plugin Parameters

RDM Support

Protocol Selection Guide

Best Practices

Network Protocols

USB Protocols

Performance

Compatibility

Configuration Example

Troubleshooting

Code References