10 This WindowManager implements simple layout switching of applications on
11 multiple layers and with different layer layouts.
14 This documentation is intended for developers and system integrators
15 who need to know, how the window manager works and how it is to be used.
17 === Scope of this Document
18 This document covers the window manager that was implemented for TMC and
19 delivered to the Automotive Grade Linux (AGL) project. It includes its
20 implementation details, concepts of operation, configuration and usage.
24 * documentation of the underlying architecture, see
25 https://wiki.automotivelinux.org/hmiframework[HMI-Framework].
26 * documentation of the AGL application framework and its technologies,
27 see https://wiki.automotivelinux.org/agl-distro/app-framework[AGL
28 Application Framework].
30 It is highly recommended to have a good understanding of these documents
31 and projects before using the window manager.
34 Currently there are a couple of known issues:
36 * Weston seems not to redraw the screen correctly. When the window
37 manager makes scene changes in quick succession, Weston seems not to
38 redraw the screen correctly and also not send wl_surface::enter
39 events, which in turn leaves applications "dead" - i.e. not rendering
40 or showing up. We developed a simple secondary ivi-controller client
41 application *redraw_fixer* (See <<_redraw_fixer,redraw_fixer>> for more)
42 that listens for specific scene-change events and issues other commands
43 that should prompt a correct redraw - however, this does not work in
45 * Only single-surface Qt applications are support through the AFBClient
46 library. This is a limitation of how Qt creates surface IDs for the
47 ivi-application interface.
49 === External libraries
50 This project includes a copy of version 2.1.1 the excellent
51 https://github.com/nlohmann/json[C++11 JSON library by Niels Lohmann].
54 A client library implementation that internally uses the _libafbwsc_, is
55 provided in the subdirectory `client-lib/` with its own documentation
58 The client library is built together with the window manager itself.
61 The window manager implements a couple of concepts in order to allow
62 efficient implementation.
65 Layers are entities that are stacked on top of each other. Each layer
66 has an ID which is used for the ivi-controller interface, but this ID
67 also implicitly specifies its stacking order, from lowest to highest.
69 Layers are always full-screen. We do not use layer dimensions as a way
70 to setup the scene, rather - each layer has a layout attached to it,
71 which specifies an area that is used by surfaces to draw on.
73 Additionally, layers will generally leave surfaces on below layers
74 activated, and only disable surfaces on layers the are above the
77 It is possible to deactivate these surfaces on lower layers explicitly
78 using the `DeactivateSurface` API call.
81 Surfaces are _placed_ on layers according to their name. The surface
82 will then be resized to dimensions, according to the layer's layout
86 The binding API consists of a couple of AFB _verbs_ - that is; function
87 calls to the Window Manager.
90 Each function returns a reply containing at least a failed or successful
91 result of the call, additionally, when calls return something, it is
92 noted. The notation used has the following meaning:
95 FunctionName(argument_name: argument_type)[: function_return_type]
98 Where the return type may be omitted if it is void.
100 * `RequestSurface(drawing_name: string): int`
101 Request a surface ID for the given name. This name and ID association
102 will live until the surface is destroyed (or e.g. the application
103 exits). Each surface that is managed by the window manager needs to
104 call this function first!
105 * `ActivateSurface(drawing_name: string)`
106 This function requests the activation of a surface. It usually is not
107 called by the application, but rather by the application framework or
109 * `DeactivateSurface(drawing_name: string)`
110 Request deactivation of a surface. This function is not usually called
111 by applications themselves, but rather by the application framework or
113 * `EndDraw(drawing_name: string)`
114 Signals the window manager, that the surface is finished drawing. This
115 is useful for consistent flicker-free layout switches, see the
116 Architecture document for details.
118 There are a couple of non-essential (mostly for debugging and
119 development) API calls:
121 * `list_drawing_names(): json`
122 List known surface _name_ to _ID_ associations.
124 Ping the window manager. Does also dispatch pending events if any.
125 * `debug_status(): json`
126 Returns a json representation of the current layers and surfaces known
127 to the window manager. This represents the wayland-ivi-extension
129 * `debug_surfaces(): json`
130 Returns a json representation of all surfaces known to the window
131 manager. This represents the wayland-ivi-extension properties of the
133 * `debug_layers(): json`
134 Returns the current layer configuration, as configured through
136 * `debug_terminate()`
137 Terminates the afb-daemon running the window manager binding, if the
138 environment variable `WINMAN_DEBUG_TERMINATE` is set.
141 The window manager broadcasts certain events (to all applications) that
142 signal information on the state of the surface regarding the current
145 * `Active(drawing_name: string)`
146 Signal that the surface with the name `drawing_name` is now active.
147 * `Inactive(drawing_name: string)`
148 Signal that the surface with the name `drawing_name` is now inactive.
149 This usually means, the layout got changed, and the surface is now
150 considered inactive (or sleeping).
151 * `Visible(drawing_name: string)`
152 Signal applications, that the surface with name `drawing_name` is now
154 * `Invisible(drawing_name: string)`
155 Signal applications that the surface with name `drawing_name` is now
157 * `SyncDraw(drawing_name: string)`
158 Signal applications, that the surface with name `drawing_name` needs
159 to redraw its content - this usually is sent when the surface geometry
161 * `FlushDraw(drawing_name: string)`
162 Signal to applications, that the surface with name `drawing_name` can
163 now be swapped to its newly drawn content as the window manager is
164 ready to activate a new layout (i.e. a new surface geometry).
166 === Binding API Usage
167 For a detailed description on how the binding API is supposed to be
168 used, refer to the Architecture document.
171 The window manager is configured with the _layers.json_ configuration
172 file, by default it is searched in `/etc/layers.json` but through the
173 use of the environment variable `LAYERS_JSON` the WM can be instructed
174 to use different file. Note, that the WM will not run unless this
175 configuration is found and valid.
177 A sample configuration is provided with the window manager
178 implementation, this sample is installed to /etc/layers.json.
180 === Configuration Items
181 This section describes configuration items available through
182 `layers.json`. It will do this, by first providing an example, and then
183 going into its components.
188 "surface_role": "HomeScreen",
192 The `main_surface` object describes a surface that will internally be
193 treated as the main surface - usually this mean _HomeScreen_. The only
194 special handling this surface receives, is that it is not allowed to
195 deactivate it. Placement of this surface on an layer is done by the
196 other configuration described below.
198 * `surface_role` this configuration item specifies the name of the main
199 surface. Set this to e.g. `HomeScreen`.
202 This configuration item is a list of surface-name to layer mappings.
204 ===== surface to layer mapping
208 "role": "^HomeScreen$",
209 "name": "HomeScreen",
211 "area": { "type": "full" },
217 "area": { "type": "rect",
227 Each mapping defines the following items to map corresponding surfaces
230 * `role` defines a regular expression that application drawing names are
231 matched against. If applications match tis regular expression, the
232 surface will be visible on this layer.
233 * `name` is just a name definition for this layer, it has no functional use
234 apart from identifying a layer with a name.
235 * `layer_id` specifies which ID this layer will use.
236 * `area` is an object that defines the area assigned to surfaces.
237 * `split_layouts` is an optional item, that - if present - defines a
238 number of possible split-screen layouts for this layer.
241 Areas can be either `full` or `rect`, whereas `full` means a full-screen
242 layer, this is mostly useful for the main_surface or HomeScreen layer.
243 `rect` declares a layer drawing area specified as a rectangle with
244 start coordinates `x` and `y` as well as its dimensions `width` and
247 The dimensions can be specified relative to the screen dimensions. For
248 this negative values for width and height mus be used.
250 For example, a full-screen surface can have the following `rect`
260 A surface that leaves a 200pixel margin on the top and bottom can use
261 the following `rect` definition:
270 So the expression for the actual surface dimensions when using
271 screen-size-relative values will be:
274 actual_width = screen_width + 1 + width
275 actual_height = screen_height + 1 + height
278 Or in other words, to leave an `N` wide border around a surface, the
279 actual value in the dimension configuration needs to be `-N - 1`, and
280 appropriate offsets need to be set for `x` and `y`.
283 This configuration item allows the specification of split-screen layouts
284 on layers for certain surfaces.
286 A split screen layout always has a _main_ surface and a _sub_
287 surface. In order to enter a split screen layout, first the _main_
288 surface of the layout must be activated, and then the _sub_ surface. In
289 order to disable the split layout, one of the two participating surface
290 must be deactivated (or a surface on a layer below the current one
296 "name": "Media Player",
297 "main_match": "^App MPlayer Main$",
298 "sub_match": "^App MPlayer Sub",
303 A split layout object has the following attributes:
305 * `name` defines its name, it has no actual function other then a way to
306 identify this split layout.
307 * `main_match` is a regular expression that matches for the _main_
308 surface of this split layout.
309 * `sub_match` is a regular expression that matches for the _sub_ surface
312 In the above example only the surface with drawing name
313 `App MPlayer Main` will be used as the _main_ surface, but all surfaces
314 that begin with `App MPlayer Sub` can be used as a _sub_ surface for
319 The names must still match the layer's role match!
322 == Building and Running
325 This project is intended to be build with the 4.0 release of AGL.
327 Build dependencies are as follows:
331 * wayland-client >= 1.11
334 === Build Configuration
335 Use cmake to configure a build tree:
345 A couple of build options to configure the build are available:
347 * `ENABLE_DEBUG_OUTPUT:BOOL` Compiles including very verbose debug
348 output from the window manager, use --verbose three times on an
349 afb-daemon instance to see the debug messages.
350 * `ENABLE_SCOPE_TRACING:BOOL` Enables a simple scope tracing mechanism
351 used for a rather small portion of the window manager code. However,
352 it is used quite extensively in the AFBClient implementation.
354 By default these options will be disabled.
357 With the actual window manager implementation, two general utilities are
361 A shell script, that wraps `afb-client-demo` and issues commands to the
362 window manager using the AFB exposed API. It will call synchronously to
363 the WM, and output any events that are happening in the meantime.
364 Replies are printed to stdout using an failed/success annotation and a
365 dump of the actual json reply from the AFB. When found on the system, it
366 will use `pygmentize` to apply syntax highlighting to the returned JSON.
371 $ wm-request list_drawing_names
372 ON-REPLY 1:winman/list_drawing_names: OK
386 $ wm-request activatesurface App1
387 ON-REPLY 1:winman/activatesurface: OK
397 $ wm-request activatesurface AppThatDoesNotExist
398 ON-REPLY 1:winman/activatesurface: ERROR
403 "info":"Surface does not exist"
409 This utility is intended to be ran alongside the compositor, it will
410 listen for certain events regarding surfaces, and issue a couple of
411 other commands, to hopefully trigger a redraw of the surface in the
414 It will print messages for each acted-upon event, and exit when the
417 == Implementation Notes
418 The window manager is implemented as a app-framework-binder binding. That
419 means, the build produces one shared object that exports a binding
422 === Binding code generation
423 The binding API is rather simple; functions receive a json object
424 describing arguments and return a json object describing the result or
425 an error. In order to simplify development, the
426 `generate-binding-glue.py` script was added, that contains a description
427 of the API as a python dictionary. This script generates the header
428 `afb_binding_api.hpp` and the afb binding functions as
429 `afb_binding_glue.inl`. Where the latter is included in `main.cpp`.
431 Each function for the AFB binding that is generated does the following:
433 * Lock the binding mutex, so that we serialize all access to the
435 * Do some debug logging (if wanted).
436 * Check the binding state, i.e. the compositor might have exited
437 unexpectedly at which point it would not make sense to continue.
438 * Extract the arguments from the json object that is provided (doing
439 some primitive type checking).
440 * Call the afb_binding_api method corresponding to this binding function
441 * Check the afb_binding_api's function return value, log an error state
442 and return the result to the afb request.
444 The generated functions do also check for any "loose" exception that
445 comes out of the afb_binding_api call (which in turn might call the
446 actual non-trivial implementation in `App`). However, *IF* an exception
447 is thrown and not handled inside the afb_binding_call, that internal
448 state of the window manager might be broken at this time (hence the
449 talkative error log).
452 The implementation is loosely split across the following source files:
454 * `main.cpp`: The program entry point as used by the afb-daemon. This
455 file defines the afbBindingV2 symbol tat is used by the afb-daemon in
456 order to load a binding. It also defines the wayland fd event
457 dispatcher and some globals to be used (as context for the afb calls
459 * `afb_binding_api.cpp`: The implementation of the afb binding
460 functions. The actual functions are generated by
461 `generate-binding-glue.py` which generates a *.inl* file that is
462 included by `main.cpp`.
463 * `app.cpp` / `app.hpp`: This is the main application logic
465 * `config.cpp` / `config.hpp`: Very simple configuration item interface.
466 * `controller_hooks.hpp`: hook functions called by the wayland
467 controller to call into the App instance. Only a very limited number
468 of events are passed to the Application, which allowed the usage of
469 such a simple interface.
470 * `json_helper.cpp` / `json_helper.hpp`: Smaller json related helper
472 * `layers.cpp` / `layers.hpp`: Actually hold all the data from
473 layers.json configuration, do some transformations and service the App
475 * `layout.cpp` / `layout.hpp`: Very simple layout state for the
476 implementation of split layouts and tracking of the surfaces involved.
477 * `policy.hpp`: PolicyManager implementation stub. Gets passed the
478 current and new layout on layout switch and can decide upon it being
480 * `result.hpp`: Simple result class around `std::experimental::optional`
481 that additionally can hold a `char const *` to describe the error.
482 * `util.cpp` / `util.hpp`: general utility functions and structs - and
483 preprocessor definitions (e.g. `log*()` to AFB logging functions.
484 * `wayland.cpp` / `wayland.hpp`: A C++ object-oriented libwayland-client
485 wrapper. It is instanced in `main.cpp` and handles all our wayland
488 // vim:set ft=asciidoc tw=72 spell spelllang=en_US: