[apps/agl-service-windowmanager-2017.git] / doc / ApplicationGuide.md

**Window Manager Application Guide**
====
<div align="right">Revision: 0.2Final</div>
<div align="right">TOYOTA MOTOR CORPORATION</div>
<div align="right">23rd/Oct/2017</div>

* * *
<div id="Table\ of\ content"></div>

Table of content  
============
- [Introduction](#Introduction)
        - [Intended audience](#Intended\ audience)
        - [Scope of this Document](#Scope\ of\ this\ Document)
        - [Known Issues](#Known\ Issues)
        - [External libraries](#External\ libraries)
        - [Client Library](#Client\ Library)
- [Concepts](#Concepts)
        - [Layers](#Layers)
        - [Surfaces](#Surfaces)
- [Configuration](#Configuration)
        - [Configuration Items](#Configuration\ Items)
- [Building and Running](#Building\ and\ Running)
        - [Dependencies](#Dependencies)
        - [Build Configuration](#Build\ Configuration)
- [Implementation Notes](#Implementation\ Notes)
        - [Binding code generation](#Binding\ code\ generation)
        - [Structure](#Structure)
- [Sequence](#Sequence)
- [Binding API](#Binding\ API)
        - [LibWindowmanager](#LibWindowmanager)
        - [Methods](#Methods)
        - [Errors](#Errors)
        - [Usage](#Usage)
        - [Events](#Events)
- [Sample](#Sample)


<div id="Introduction"></div>

Introduction
============

This WindowManager implements simple layout switching of applications on
multiple layers and with different layer layouts.

<div id="Intended\ audience"></div>

Intended audience
-----------------

This documentation is intended for developers and system integrators who
need to know, how the window manager works and how it is to be used.

<div id="Scope\ of\ this\ Document"></div>

Scope of this Document
----------------------

This document covers the window manager that was implemented for TMC and
delivered to the Automotive Grade Linux (AGL) project. It includes its
implementation details, concepts of operation, configuration and usage.

It does not include

-   documentation of the underlying architecture, see
    [HMI-Framework](https://wiki.automotivelinux.org/hmiframework).

-   documentation of the AGL application framework and its technologies,
    see [AGL Application
    Framework](https://wiki.automotivelinux.org/agl-distro/app-framework).

It is highly recommended to have a good understanding of these documents
and projects before using the window manager.

<div id="Known\ Issues"></div>

Known Issues
------------

Currently there is a one known issues:

-   Only single-surface Qt applications are support through the
    libwindowmanager library. This is a limitation of how Qt creates surface
    IDs for the ivi-application interface.

<div id="External\ libraries"></div>

External libraries
------------------

This project includes a copy of version 2.1.1 the excellent [C++11 JSON
library by Niels Lohmann](https://github.com/nlohmann/json).

<div id="Client\ Library"></div>

Client Library
--------------

A client library implementation that internally uses the *libafbwsc*, is
provided in the subdirectory `libwindowmanager/` with its own documentation
directory.

The client library is built together with the window manager itself.

<div id="Concepts"></div>

Concepts
========

The window manager implements a couple of concepts in order to allow
efficient implementation.

<div id="Layers"></div>

Layers
------

Layers are entities that are stacked on top of each other. Each layer
has an ID which is used for the ivi-controller interface, but this ID
also implicitly specifies its stacking order, from lowest to highest.

Layers are always full-screen. We do not use layer dimensions as a way
to setup the scene, rather - each layer has a layout attached to it,
which specifies an area that is used by surfaces to draw on.

Additionally, layers will generally leave surfaces on below layers
activated, and only disable surfaces on layers the are above the
currently used layer.

It is possible to deactivate these surfaces on lower layers explicitly
using the `DeactivateSurface` API call.

<div id="Surfaces"></div>

Surfaces
--------

Surfaces are *placed* on layers according to their name. The surface
will then be resized to dimensions, according to the layer's layout
configuration.


<div id="Configuration"></div>

Configuration
=============

The window manager is configured with the *layers.json* configuration
file, by default it is searched in `/etc/layers.json` but through the
use of the environment variable `LAYERS_JSON` the WM can be instructed
to use different file. Note, that the WM will not run unless this
configuration is found and valid.

A sample configuration is provided with the window manager
implementation, this sample is installed to /etc/layers.json.

<div id="Configuration\ Items"></div>

Configuration Items
-------------------

This section describes configuration items available through
`layers.json`. It will do this, by first providing an example, and then
going into its components.

### main\_surface

    "main_surface": {
       "surface_role": "HomeScreen",
    },

The `main_surface` object describes a surface that will internally be
treated as the main surface - usually this mean *HomeScreen*. The only
special handling this surface receives, is that it is not allowed to
deactivate it. Placement of this surface on an layer is done by the
other configuration described below.

-   `surface_role` this configuration item specifies the name of the
    main surface. Set this to e.g. `HomeScreen`.

### mappings

This configuration item is a list of surface-name to layer mappings.

#### surface to layer mapping

    "mappings": [
      {
         "role": "^HomeScreen$",
         "name": "HomeScreen",
         "layer_id": 1000,
         "area": { "type": "full" },
         "comment": "Single layer map for the HomeScreen, XXX: type is redundant, could also check existence of id/first_id+last_id"
      },
      {
         "role": "MediaPlayer|Radio|Phone|Navigation|HVAC|Settings|Dashboard|POI|Mixer",
         "name": "apps",
         "layer_id": 1001,
         "area": { "type": "rect", "rect": { "x": 0, "y": 218, "width": -1, "height": -433 } },
         "comment": "Range of IDs that will always be placed on layer 1001, negative rect values are interpreted as output_size.dimension - $value",

         "split_layouts": [
            {
               "name": "Navigation",
               "main_match": "Navigation",
               "sub_match": "HVAC|MediaPlayer",
               "priority": 1000
            }
         ]
      },
      {
         "role": "^OnScreen.*",
         "name": "popups",
         "layer_id": 9999,
         "area": { "type": "rect", "rect": { "x": 0, "y": 760, "width": -1, "height": 400 } },
         "comment": "Range of IDs that will always be placed on the popup layer, that gets a very high 'dummy' id of 9999"
      }
    ]

Each mapping defines the following items to map corresponding surfaces
to a layer.

-   `role` defines a regular expression that application drawing names
    are matched against. If applications match tis regular expression,
    the surface will be visible on this layer.

-   `name` is just a name definition for this layer, it has no
    functional use apart from identifying a layer with a name.

-   `layer_id` specifies which ID this layer will use.

-   `area` is an object that defines the area assigned to surfaces.

-   `split_layouts` is an optional item, that - if present - defines a
    number of possible split-screen layouts for this layer.

#### Area

Areas can be either `full` or `rect`, whereas `full` means a full-screen
layer, this is mostly useful for the main\_surface or HomeScreen layer.
`rect` declares a layer drawing area specified as a rectangle with start
coordinates `x` and `y` as well as its dimensions `width` and `height`.

The dimensions can be specified relative to the screen dimensions. For
this negative values for width and height mus be used.

For example, a full-screen surface can have the following `rect`
definition:

    "rect": { "x": 0,
              "y": 0,
              "width": -1,
              "height": -1 }

A surface that leaves a 200pixel margin on the top and bottom can use
the following `rect` definition:

    "rect": { "x": 0,
              "y": 200,
              "width": -1,
              "height": -401 }

So the expression for the actual surface dimensions when using
screen-size-relative values will be:

    actual_width = screen_width + 1 + width
    actual_height = screen_height + 1 + height

Or in other words, to leave an `N` wide border around a surface, the
actual value in the dimension configuration needs to be `-N - 1`, and
appropriate offsets need to be set for `x` and `y`.

#### split\_layouts

This configuration item allows the specification of split-screen layouts
on layers for certain surfaces.

A split screen layout always has a *main* surface and a *sub* surface.
In order to enter a split screen layout, first the *main* surface of the
layout must be activated, and then the *sub* surface. In order to
disable the split layout, one of the two participating surface must be
deactivated (or a surface on a layer below the current one must be
activated).

    "split_layouts": [
       {
           "name": "Navigation",
           "main_match": "Navigation",
           "sub_match": "HVAC|MediaPlayer",
       }
    ]

A split layout object has the following attributes:

-   `name` defines its name, it has no actual function other then a way
    to identify this split layout.

-   `main_match` is a regular expression that matches for the *main*
    surface of this split layout.

-   `sub_match` is a regular expression that matches for the *sub*
    surface of this layout.

In the above example only the surface with drawing name
`App MPlayer Main` will be used as the *main* surface, but all surfaces
that begin with `App MPlayer Sub` can be used as a *sub* surface for
this layout.

The names must still match the layer's role match!

<div id="Building\ and\ Running"></div>

Building and Running
====================

<div id="Dependencies"></div>

Dependencies
------------

This project is intended to be build with the 4.0 release of AGL.

Build dependencies are as follows:

-   afb-daemon &gt;= 1.0

-   libsystemd &gt;= 222

-   wayland-client &gt;= 1.11

-   cmake &gt;= 3.6.1

<div id="Build\ Configuration"></div>

Build Configuration
-------------------

**Download recipe**
If repo is already done, please start with git clone
```
$ mkdir WORK
$ cd WORK
$ repo init -b dab -m dab_4.0.0_xml -u https://gerrit.automotivelinux.org/gerrit/AGL/AGL-repo
$ repo sync
$ git clone https://gerrit.automotivelinux.org/gerrit/staging/meta-hmi-framework

```

Then you can get the following recipe.
* `meta-hmi-framework/windowmanager`


**Bitbake**
```
$ source meta-agl/scripts/aglsetup.sh -m m3ulcb agl-demo agl-devel agl-appfw-smack agl-hmi-framework
$ bitbake agl-service-windowmanager-2017
```


A couple of build options to configure the build are available:

-   `ENABLE_DEBUG_OUTPUT:BOOL` Compiles including very verbose debug
    output from the window manager, use --verbose three times on an
    afb-daemon instance to see the debug messages.

-   `ENABLE_SCOPE_TRACING:BOOL` Enables a simple scope tracing mechanism
    used for a rather small portion of the window manager code. However,
    it is used quite extensively in the libwindowmanager implementation.

By default these options will be disabled.


<div id="Implementation\ Notes"></div>

Implementation Notes
====================

The window manager is implemented as a app-framework-binder binding.
That means, the build produces one shared object that exports a binding
interface.

<div id="Binding\ code\ generation"></div>

Binding code generation
-----------------------

The binding API is rather simple; functions receive a json object
describing arguments and return a json object describing the result or
an error. In order to simplify development, the
`generate-binding-glue.py` script was added, that contains a description
of the API as a python dictionary. This script generates the header
`afb_binding_api.hpp` and the afb binding functions as
`afb_binding_glue.inl`. Where the latter is included in `main.cpp`.

Each function for the AFB binding that is generated does the following:

-   Lock the binding mutex, so that we serialize all access to
    the binding.

-   Do some debug logging (if wanted).

-   Check the binding state, i.e. the compositor might have exited
    unexpectedly at which point it would not make sense to continue.

-   Extract the arguments from the json object that is provided (doing
    some primitive type checking).

-   Call the afb\_binding\_api method corresponding to this binding
    function

-   Check the afb\_binding\_api’s function return value, log an error
    state and return the result to the afb request.

The generated functions do also check for any "loose" exception that
comes out of the afb\_binding\_api call (which in turn might call the
actual non-trivial implementation in `App`). However, **IF** an
exception is thrown and not handled inside the afb\_binding\_call, that
internal state of the window manager might be broken at this time (hence
the talkative error log).

<div id="Structure"></div>

Structure
---------

The implementation is loosely split across the following source files:

-   `main.cpp`: The program entry point as used by the afb-daemon. This
    file defines the afbBindingV2 symbol tat is used by the afb-daemon
    in order to load a binding. It also defines the wayland fd event
    dispatcher and some globals to be used (as context for the afb calls
    we receive).

-   `afb_binding_api.cpp`: The implementation of the afb
    binding functions. The actual functions are generated by
    `generate-binding-glue.py` which generates a **.inl** file that is
    included by `main.cpp`.

-   `app.cpp` / `app.hpp`: This is the main application
    logic implementation.

-   `config.cpp` / `config.hpp`: Very simple configuration
    item interface.

-   `controller_hooks.hpp`: hook functions called by the wayland
    controller to call into the App instance. Only a very limited number
    of events are passed to the Application, which allowed the usage of
    such a simple interface.

-   `json_helper.cpp` / `json_helper.hpp`: Smaller json related
    helper functions.

-   `layers.cpp` / `layers.hpp`: Actually hold all the data from
    layers.json configuration, do some transformations and service the
    App implementation.

-   `layout.cpp` / `layout.hpp`: Very simple layout state for the
    implementation of split layouts and tracking of the
    surfaces involved.

-   `policy.hpp`: PolicyManager implementation stub. Gets passed the
    current and new layout on layout switch and can decide upon it being
    valid or not.

-   `result.hpp`: Simple result class around
    `std::experimental::optional` that additionally can hold a
    `char const *` to describe the error.

-   `util.cpp` / `util.hpp`: general utility functions and structs - and
    preprocessor definitions (e.g. `log*()` to AFB logging functions.

-   `wayland.cpp` / `wayland.hpp`: A C++ object-oriented
    libwayland-client wrapper. It is instanced in `main.cpp` and handles
    all our wayland needs.

<div id="Sequence"></div>

Sequence
===============

To understand the sequence between application and window manager, refer to the [spec documentation](https://wiki.automotivelinux.org/windowmanager).


<div id="Binding\ API"></div>

Binding API
===============

Each function returns a reply containing at least a failed or successful
result of the call, additionally, when calls return something, it is
noted.

<div id="LibWindowmanager"></div>

LibWindowmanager
------

This is the public interface of the class `LibWindowmanager`.

    class LibWindowmanager
    {
    public:
        LibWindowmanager();
        ~LibWindowmanager();

        enum EventType {
           Event_Active = 0,
           Event_Inactive,

           Event_Visible,
           Event_Invisible,

           Event_SyncDraw,
           Event_FlushDraw,
        };

        int init(int port, char const *token);

        // WM API
        int requestSurface(json_object *object);
        int activateSurface(json_object *object);
        int deactivateSurface(json_object *object);
        int endDraw(json_object *object);

        void set_event_handler(enum EventType et, handler_fun f);

    };

<div id="Methods"></div>

Methods
-------

### init(int port, char const *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`.

### requestSurface(json_object *object)

**args: `{ 'kKeyDrawingName': 'application name' }`**  
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.

### activateSurface(json_object *object)

**args: `{ 'kKeyDrawingName': 'application name', 'kKeyDrawingArea': 'layout'  }`**  
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.

### deactivateSurface(json_object *object)

**args: `{ 'kKeyDrawingName': 'application name' }`**  
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.

### endDraw(json_object *object)

**args: `{ 'kKeyDrawingName': 'application name' }`**  
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.

### set\_event\_handler(enum EventType et, handler_fun f)

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.

<div id="Errors"></div>

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.

<div id="Usage"></div>

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* applications, 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.

<div id="Events"></div>

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.

-   `Active(json_object *object)`  
    args: { 'kKeyDrawingName': 'application name' }  
    Signal that the surface with the name
    `kKeyDrawingName` is now active.

-   `Inactive(json_object *object)`  
    args: { 'kKeyDrawingName': 'application name' }  
    Signal that the surface with the
    name `kKeyDrawingName` is now inactive. This usually means, the layout
    got changed, and the surface is now considered inactive
    (or sleeping).

### Visible and Invisible

These events signal an application that it was switched to be visible or
invisible respectively. These events also are handled implicitly through
the wayland protocol by means of `wl_surface::enter` and
`wl_surface::leave` events to the client.

-   `Visible(json_object *object)`  
    args: { 'kKeyDrawingName': 'application name' }  
    Signal applications, that the
    surface with name `kKeyDrawingName` is now visible.

-   `Invisible(json_object *object)`  
    args: { 'kKeyDrawingName': 'application name' }  
    Signal applications that the
    surface with name `kKeyDrawingName` is now invisible.

### 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.

-   `SyncDraw(json_object *object)`  
    args: { 'kKeyDrawingName': 'application name', 'kKeyDrawingArea': 'layout'  }  
    Signal applications, that the
    surface with name `kKeyDrawingArea` needs to redraw its content - this
    usually is sent when the surface geometry changed.

-   `FlushDraw(json_object *object)`  
    args: { 'kKeyDrawingName': 'application name' }  
    Signal applications, that the
    surface with name `kKeyDrawingArea` can now be swapped to its newly
    drawn content as the window manager is ready to activate a new
    layout (i.e. a new surface geometry).

<div id="Sample"></div>

Sample
============

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.

Repo: `apps/agl-service-homescreen-2017`  
Path: `sample/template/main.c`