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XDisplay Architecture

XDisplay is a high-performance cross-platform virtual display solution designed for extremely low-latency desktop extension to Android devices.

High-Level Overview

graph TD
    subgraph Host [Linux Host - Rust]
        EVDI[EVDI Kernel Module] --> |Virtual Display| DRM[DRM Device]
        DRM --> Capture[Screen Capture]
        Capture --> Encoder[H.264 Hardware Encoder]
        Encoder --> Transport[UDP/USB Transport]
    end

    subgraph Client [Android Client - Kotlin/Rust]
        Transport --> |Network| Reassembly[Native Reassembly]
        Reassembly --> MediaCodec[NDK MediaCodec]
        MediaCodec --> Surface[Surface Rendering]
    end

    Input[Touch/Keyboard] -.-> |Feedback Loop| Transport
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Core Components

1. Virtual Display (EVDI)

XDisplay utilizes the EVDI (Extensible Virtual Display Interface) kernel module to create virtual DRM devices. This allows Linux to treat the Android device as a real second monitor, complete with resolution switching and workspace management.

2. Encoder Path

The host application captures frames from the EVDI buffer and pipes them through xd-encoder. It targets H.264 (AVC) exclusively to ensure compatibility with Android hardware decoders. Raw pixel streaming is avoided to preserve bandwidth and reduce jitter.

3. Transport Layer (xd-transport)

  • UDP: Primary wireless transport. Implements a custom fragmentation and reassembly protocol optimized for real-time video (drops old frames instead of retrying).
  • USB (ADB): High-stability wired transport. Uses ADB port forwarding to tunnel traffic with minimal overhead.

4. Native Android Client

The client uses a hybrid architecture:

  • Rust (NDK): Handles high-frequency network packets and interacts directly with the Android MediaCodec C API. This bypasses Java overhead for frame queuing, achieving sub-16ms latency.
  • Kotlin (Compose): Manages the discovery UI, connection state, and provides a Java-based decoder fallback for maximum compatibility.

Security

  • All communication is designed for local networks.
  • No cloud dependencies; data stays on your local hardware.
  • Source code is open under AGPLv3.