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diff --git a/docs/6_Component_Documentation/3_waltham-receiver_waltham-transmitter.md b/docs/6_Component_Documentation/3_waltham-receiver_waltham-transmitter.md new file mode 100644 index 0000000..b98de32 --- /dev/null +++ b/docs/6_Component_Documentation/3_waltham-receiver_waltham-transmitter.md @@ -0,0 +1,96 @@ +--- +title: Waltham receiver/transmitter +--- + +# Waltham + +[Waltham protocol](https://github.com/waltham/waltham) is a IPC library similar +to [Wayland](https://wayland.freedesktop.org), 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](1_agl-compositor.md#private-extensions) protocol and inform +the compositor that it should migrate it to other, remote outputs. |