**Table of Content** 1. TOC {:toc} ## waltham-client-server-applications ![image](./images/Waltham_Architecture.jpg) ### waltham-client waltham-client uses Waltham IPC library to connect to remote and transmit client buffers using GStreamer framework. It is designed for AGL upon certain Linux base system with wayland backend. waltham-client is divided into two components: * waltham-transmitter plugin: waltham-transmitter plugin provides API to create remote connections and push surfaces over the network and handles both remote output and remote input. * waltham-renderer: waltham-renderer is the implementation for sharing surface. It creates a buffer to be transmitted to other domain. Latest implementation uses GStreamer framework. ### waltham-receiver waltham-receiver is a sample implementation of receiver app which shall be running at remote side. It is developed based on [waltham server](https://github.com/ waltham/waltham/tree/master/tests), using Waltham protocol to obtain and process remote output which is sent by waltham-transmitter. This component is designed to be used for evaluating the functionalities of waltham-transmitter plugin. ## How it works 1. Loading and initialization The system launches Weston, then Weston loads waltham-transmitter plugin. waltham-client connects to receiver app at remote side during initialization. ![image](./images/01_Load_transmitter.jpg) 2.Establishing connection At transmitter_create_remote(), waltham-transmitter creates "struct weston_transmitter_remote" which expresses the receiver object at remote side. Therefore this structure is created for each receiver. waltham-transmitter sends wth_display_get_registry() and wth_display_sync_message() to the receiver app as same manner as Wayland protocol. So that receiver app sends back the resource list to waltham-transmitter. ![image](./images/02_Establish_connection.jpg) 3. Forwarding surface While Weston redraws the surface to waltham-transmitter output, waltham-transmitter sends waltham protocol messages to receiver app to notify the surface update. wthp_surface_attach(), wthp_surface_damage() and wthp_surface_commit() which correspond to wl_surface_attach(), wl_surface_damage() and wl_surface_commit() message in wayland protocol. wthp_surface_attach() - Send wthp_buffer to a buffer handling. This is not the a ctual buffer which contains the data to be rendered but the handle of actual buffer. It abstracts the differences of buffer type. wthp_surface_damage() - Tell the updated region to the receiver app. wthp_surface_commit() - Tell surface gets updated to the receiver app. ![image](./images/03_Forward_surface.jpg) 4. Rendering using GStreamer ![image](./images/04_Rendering_using_gstreamer.jpg) 5. Input handling For handling input events, waltham-transmitter has 2 ways to secure seat. 1. Use wl_seat as weston has. 2. Create new wl_seat. Second case is applicable in the case transmitter side does not have input device but the receiver at remote side has. After wl_seat is created, waltham-transmitter sends input events to weston client application when it gets input event from receiver via waltham protocol. The message wthp_send_XXX shows you that input event is forwarded from receiver to transmitter, XXX is filled by input event name. ![image](./images/05_Input_handling.jpg) 6. Retry connection In case the connection gets disconnected during surface sharing, waltham-transmitter shall re-establish the connection. The object “struct waltham_display” represents the connection between the transmitter and receiver, which structure has the flag used to detect disconnection named “running”. In function “connection_handle_data()”, running is set to "false" in case disconnection detected. This flag is checked at every “transmitter_surface_gather_state". When running is false state, waltham-transmitter starts retry handling sequence. First of all, it release the waltham protocol objects. Second, it establishes connection sequence mentioned in "[2. Establishing connection](#EstCnnn)". ![image](./images/06_Retry_connection.jpg) ## Waltham in practice Here is the example how waltham can be used in hypervisor use case of real project. * Weston is used as the wayland compositor. * waltham-client is implemented for Weston which acts as a Waltham virtual display. * Application surface is assigned to Waltham virtual display and it's sent to the other ECU/OS. Buffers of surface are transferred via GStreamer(UDP), since transferring raw pixel data via Waltham(TCP) is not enough fast. * Controlling input events (pointer, keyboard, touch) for the surface is handled by Waltham. ![image](./images/Waltham_In_Practice.jpg) ## How Waltham can be integrated Here are possible integration examples of waltham. ### As EGL backend (theoretical possibility) Similar to Wayland backend for EGL, Waltham client could be backend in compositor. For good performance, a generic surface sharing mechanism is needed in hypervisor environment. Applications need to adapt to Waltham. Waltham is not designed with this use in mind. This usage is just a theoretical possibility. ![image](./images/Waltham_Integration_Possibility-01.jpg) ### As GStreamer sink (theoretical possibility) Similar to Wayland sink, Waltham sink GStreamer plugin can be implemented which sends the buffers to receiver on another domain/OS. Waltham sink can utilize frame sync and presentation feedback protocols for video synchronization. For good performance, a generic surface sharing mechanism is needed in hypervisor environment. Waltham is not designed with this use in mind. This usage is just a theoretical possibility. ![image](./images/Waltham_Integration_Possibility-02.jpg) ### As virtual display in compositor Virtual display plugin can be implemented in compositor. This plugin sends client buffers to waltham-receiver in another domain. No changes to applications. For good performance, a generic surface sharing mechanism is needed in hypervisor environment. This is the intended use in mind during design. ![image](./images/Waltham_Integration_Possibility-03.jpg)