Waltham
Waltham protocol is a IPC library similar to Wayland, developed with networking in mind. It operates over TCP sockets, while the wayland protocol only works locally over a UNIX socket. It retains wayland-esque paradigm, making use of XMLs to describe the protocol, and it follows an object-oriented design with an asynchronous architecture.
Differences from Wayland to Waltham
Some of the differences between Wayland and Waltham are:
- Waltham uses TCP sockets for communication
- Waltham cannot send file descriptors
- Waltham API is minimal and symmetric between server and client sides
- Waltham does not provide an event loop implementation
- The registry implementation is left out of the library, only the interface is provided
- No multi-threading support for sharing objects between threads
Waltham-transmitter and remoting plugin
Surface sharing is not part of Waltham protocol, each system needs to implement the most efficient way of passing by the buffers from one side to another. On AGL, make use of remoting-plugin to enable surface sharing which uses GStreamer as encoder/decoder. It uses libweston DRM virtual API to grab the buffers, and then to stream them over the network. The gstreamer pipeline uses UDP while the input events are communicated with Waltham protocol. The input part is handled by waltham-transmitter plugin which provides an API to create remote connections and push surfaces over the network and handles remote input. The act of pushing surface is a misnomer, kept from the older, previous implementation, and acts a notification mechanism from the transmitter side to the remote side.
The receiver client
waltham-receiver application is a wayland demo implementation which should be running at the remote side. It is using Waltham protocol to obtain and process remote input events which handled the transmitter side by the waltham-transmitter plugin. It creates a similar gstreamer pipeline to process the incoming buffers and draw and displaying them into a subsurface created by waylandsink.
Contrary to expectations, the waltham receiver is the one that implements the server side of the Waltham protocol and is capable of displaying the incoming buffers but also process input events locally and forward them with the help of the Waltham protocol back at the transmitter side, which in turn will update the image contents and stream to the receiver, showing the changes caused by that input.
ECU 1 ECU 2
+---------------------------------------------+ +--------------------------------------+
| +-----------------+ | | |
| | Application | | | +-----------+-----------+ |
| +-----------------+ | | | Gstreamer | | |
| ^ | Buffer ---------------> (Decode) | | |
| wayland | +-------------------/ | +-----------+ | |
| v | | (Ethernet) | | Waltham-receiver | |
| +----+---------------------+ | | --------------------> | |
| | | Transmitter plugin |<---------------------/ | +-----------------------+ |
| | | | | | Waltham-Protocol | ^ |
| | |---------------------| | | | wayland | |
| | | Remoting plugin |-------+ | | v |
| | | | | | +---------------------+ |
| | +---------------------+ | | | | |
| | | | | | compositor | |
| | compositor | | | | | |
| +------+-------------------+ | | +----------------+----+ |
| | | | | |
| v | | v |
| +------------+ | | +----------+ |
| | Display | | | | Display | |
| | | | | | | |
| +------------+ | | +----------+ |
+---------------------------------------------+ +--------------------------------------+
Migrating/Placing applications on other outputs
In order to start or place an application on the remoting-ouput output, we can
use agl-shell-app-id ini entry for that particular output.
[transmitter-output]
name=transmitter-1
mode=640x720@30
host=192.168.20.99
port=5005
agl-shell-app-id=<APP_ID>
Alternatively, and programmatically, one can use the agl-shell-desktop protocol and inform the compositor that it should migrate it to other, remote outputs.