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diff --git a/libwindowmanager/doc/LibWindowmanager.md b/libwindowmanager/doc/LibWindowmanager.md new file mode 100644 index 0000000..b855081 --- /dev/null +++ b/libwindowmanager/doc/LibWindowmanager.md @@ -0,0 +1,250 @@ +Introduction +============ + +The LibWindowmanager library provides a simple interface to manipulate and +query the state of the window manager application framework binding. +It is needs to be integrated and called from the client application. + +Intended audience +----------------- + +This document is intended to be useful to application developers. + +Scope of this Document +---------------------- + +This document describes the singleton class interface to the *Window +Manager* binding service. + +class LibWindowmanager +=============== + +This is the public interface of the class `LibWindowmanager`. Private members +and methods are not reproduced as they will not affect usage of the +class by client applications. + + class LibWindowmanager + { + public: + static LibWindowmanager &instance(); + + int init(int port, char const *token); + + // WM API + int requestSurface(const char *label); + int activateSurface(const char *label); + int deactivateSurface(const char *label); + int endDraw(const char *label); + + enum EventType { + Event_Active, + Event_Inactive, + Event_Visible, + Event_Invisible, + Event_SyncDraw, + Event_FlushDraw, + }; + + void set_event_handler(enum EventType et, + std::function<void(char const *label)> f); + }; + +Errors +------ + +Methods returning an `int` signal successful operation when returning +`0`. In case of an error, an error value is returned as a negative errno +value. E.g. `-EINVAL` to signal that some input value was invalid. + +Additionally, logging of error messages is done on the standard error +file descriptor to help debugging the issue. + +Labels +------ + +Surface labels are any valid strings. For `requestSurface()` these +strings must match the *Window Manager* configuration in order to be +allowed to be displayed on one layer or the other. For all other calls +the label must match the exact name of a requested surface. + +Methods +------- + +### LibWindowmanager::init(port, token) + +Initialize the Binding communication. + +The `token` parameter is a string consisting of only alphanumeric characters. +If these conditions are not met, the LibWindowmanager instance will not initialize, +i.e. this call will return `-EINVAL`. + +The `port` parameter is the port the afb daemon is listening on, an +invalid port will lead to a failure of the call and return `-EINVAL`. + +### LibWindowmanager::requestSurface(label) + +This method requests a surface with the label given from the *Window +Manager*. It will return `0` for a successful surface request, and +`-errno` on failure. Additionally, on the standard error, messages are +logged to help debgging the issue. + +### LibWindowmanager::activateSurface(label) + +This method is mainly intended for *manager* applications that control +other applications (think an application manager or the *HomeScreen*). +It instructs the window manager to activate the surface with the given +*label*. + +This method only is effective after the actual window or surface was +created by the application. + +### LibWindowmanager::deactivateSurface(label) + +This method is mainly intended for *manager* applications that control +other applications. It instructs the window manager to deactivate the +surface associated with the given label. Note, that deactivating a +surface also means to implicitly activate another (the last active or if +not available *main surface* or *HomeScreen*.) + +This method only is effective after the actual window or surface was +created by the application. + +### LibWindowmanager::endDraw(label) + +This function is called from a client application when it is done +drawing its surface content. + +It is not crucial to make this call at every time a drawing is finished +- it is mainly intended to allow the window manager to synchronize +drawing in case of layout switch. The exact semantics are explained in +the next [Events](#_events) Section. + +### LibWindowmanager::set\_event\_handler(et, func) + +This method needs to be used to register event handlers for the WM +events described in the EventType enum. Only one hendler for each +EventType is possible, i.e. if it is called multiple times with the same +EventType the previous handler will be replaced. + +The `func` handler functions will receive the label of the surface this +event is targeted at. + +See Section [Events](#_events) for mor detailed information about event +delivery to client applications. + +Usage +----- + +### Initialization of LibWindowmanager + +Before usage of the LibWindowmanager, the method `init()` must be +called once, it will return `-errno` in case of en error and log +diagnostic messages to stderr. + +### Request a surface + +When creating a surface with *Qt* - it is necessary to request a surface +from the WM, internally this will communicate with the window manager +binding. Only after `requestSurface()` was successful, a surface should +be created. + +This is also true for *QML* aplications, where only after the +`requestSurface()` should the load of the resource be done. The method +returns `0` after the surface was requested successfully. + +#### Workings of requestSurface() + +`LibWindowmanager::requestSurface()` calls the AFB binding verb +`requestsurface` of the `windowmanager` API. This API call will return a +numeric ID to be used when creating the surface. This ID is never +explicitly returned to the client application, instead, it is set in the +application environment in order for *Qt* to then use it when creating +the surface. + +With the current *Qt* implementation this means, that only one surface +will be available to client applications, as subsequent windows will +increment this numeric ID internally - which then will lead to IDs that +cannot be known by the window manager as there is no direct +communication from *Qt* to the WM. + +Events +------ + +Events are a way for the *Window Manager* to propagate information to +client applications. It was vital for the project to implement a number +of events, that mirror functionality that is already present in the +wayland protocol. + +All events have the surface `label` as argument - a way to enable future +multi-surface applications. + +As already stated above, this is currently not possible with the way +*Qt* implements its surface ID setting. + +### Active and Inactive Events + +These events signal an application that it was activated or deactivated +respectively. Usually this means it was switched visible - which means +the surface will now be on the screen and therefor continue to render. + +### Visible and Invisible + +These events signal an application that it was switched to be visible or +invisible respectively. These events too are handled implicitly through +the wayland protocol by means of `wl_surface::enter` and +`wl_surface::leave` events to the client. + +### SyncDraw and FlushDraw + +These events instruct applications that they should redraw their surface +contents - again, this is handled implicitly by the wayland protocol. + +`SyncDraw` is sent to the application when it has to redraw its surface. + +`FlushDraw` is sent to the application when it should swap its buffers, +that is *signal* the compositor that its surface contains new content. + +Example Use Case +---------------- + +In order to enable application to use the `WM` surface registration +function the above described steps need to be implemented. + +As a minimal example the usage and initialization can look like the +following. + + // Assume a program argc and argv. + QGuiApplication app(argc, argv); + + auto &wm = LibWindowmanager::instance(); + + // initialize the LibWindowmanager binding. + if(wm.init(1234, "wmtest") != 0) { + exit(EXIT_FAILURE); + } + + // Request a surface label from the WM. + char const *surface_label = "AppMediaPlayer"; + if (wm.requestSurface(surface_label) != 0) { + exit(EXIT_FAILURE); + } + + // Register an Active event handler. + wm.set_event_handler(Event_Active, + [](char const *label) { + qDebug() << "Surface" << label << "got activated"; + }); + + // Initialize application window + // ... + + // request to activate the surface, this should usually + // not be done by the client application. + if (wm.activateSurface(surface_label) != 0) { + fprintf(stderr, "Could not activate the surface\n"); + exit(EXIT_FAILURE); + } + + // e.g. exec the qt application + app.exec(); + |