Debug & Modify Wayland Capture

This skill helps you navigate src/screencopy_capture.rs and debug issues related to Wayland screen capture (wlr-screencopy-unstable-v1).

🧠 Context

The capture module is responsible for:

1. •Connecting to the Wayland display.
2. •Requesting frames via zwlr_screencopy_manager_v1.
3. •Handling buffer copy (Linux DMABUF or POSIX SHM).
4. •Handling "buffer done" events to feed the encoder.

🛠️ Common Issues & Fixes

1. "Protocol not found" or "Compositor not supported"

Symptom: The app crashes at startup claiming the global interface is missing. Cause: The compositor does not support wlr-screencopy-unstable-v1. Verification:

# Check if the Wayland global is available
wayland-info | grep screencopy

Fix: Ensure you are using Sway, Hyprland, Wayfire, or a wlroots compositor. GNOME/Mutter is not supported.

2. Black Screen / Invalid Buffer

Symptom: Stream is connected but video is black or garbage. Cause: Mismatched buffer strides or pixel formats. Debugging:

• •Inspect the frame events in screencopy_capture.rs.
• •Add logging to print buffer_width, buffer_height, stride, and format.

// In src/screencopy_capture.rs
tracing::debug!("Format: {:?}, Stride: {}", format, stride);

• •The encoder expects AV_PIX_FMT_BGR0 or AV_PIX_FMT_BGRA. If the compositor sends XRGB8888, ensure the colorspace conversion handles it.

3. High Latency / Laggy Capture

Cause: Blocking the Wayland event loop or slow copy. Check:

• •Ensure event_queue.dispatch() is called frequently.
• •Verify we are using DMABUF (zero-copy) if possible, though currently the project might rely on mmap (SHM).

🚀 Key Code Paths

src/screencopy_capture.rs

• •Capture::new(): Usage of GlobalManager to find zwlr_screencopy_manager_v1.
• •capture_output(): The main loop where we ask for capture_output.
• •FrameHandler: Callbacks for buffer, linux_dmabuf, buffer_done.

🧪 Verification Commands

Run with debug logs to see protocol events:

RUST_LOG=hdmi_wifi=debug,wayland_client=debug ./target/release/hdmi-wifi