MuditaOS/module-gui

Graphic User Interface

This article includes details on how MuditaOS widgets are rendered and how the GUI handles key pressing.

Introduction

How widgets are rendered

• All widgets are children of gui::Item
• There are two major commands to trigger screen redraw:
  • gui::Item::buildDrawList in each gui::Item - uses gui::Items tree to builds draw commands
  • app::Application::refreshWindow in app::Application - triggers update on display on message: gui::AppRefreshMessage (final draw on screen done with: app::Application::render)
• All interface actions can be made with either:
  • gui::Item callbacks, which are in [callbacks](@ref callbacks "Item callbacks"), or
  • gui::Item virtual functions, [callback functions](@ref callbackCallers) When overriding please mind that you might want to use ancestor function inside too to i.e. not loose key presses etc.
• All gui::Item are able to handle keyPresses via gui::InputEvent
• All gui::Item are able to traverse down on their gui::Item::children and know which child has gui::Item::focusItem at the time

How does it work on the application side

Please see app::Application, app::manager::ApplicationManager for detailed information on how messages are handled between both. This is just general documentation.

These actions are done on a chained bus request between: app::Application, app::manager::ApplicationManager and sapm::EventWorker

All of these are asynchronous and there is little state machine maintenance.

1. app::Application has it's own state which is managed both in application and in manager (via setters and getters)
2. sapm::ApplicationManager has it's own state which tells what exactly it's processing right now

Note: All app::Application:

1. Register and initialize their windows on start of the application in app::Application::createUserInterface
2. Need to pass app::Application::DataReceivedHandler first to parent function call to properly handle bus messages
3. Have windows based on gui::AppWindow

Note: When it comes to gui::AppWindow:

1. gui::AppWindow::buildInterface has to call parent build interface first. Otherwise elements for child won't be created and it will crash
2. gui::AppWindow::onInput has to call parent onInput, otherwise handling key presses will fail
3. Applications react on key releases actions, in most scenarios key press event is useless
4. all applications, if it hasn't been overriden in gui::AppWindow will try to return to previous window or application on back

gui::Item Key Press handling

What happens when you press a key?

• bsp handles key press on I2C IRQ and sends Event to event worker on naked FreeRTOS pipe (on target RT1051, on Linux gtk does that)
• EventWorker worker of EventService:
  • handles the press and sends it to current Application
  • with focus (Note: when no application is in focus this will not work)
• application can either:
  • process gui::InputEvent with RawKey or gui::KeyInputSimpleTranslation
  • use callbacks (see how to handle key press below)
  • use widgets which override default key handling (see gui::Item::onInput)
  • have own gui::KeyInputMappedTranslation + gui::InputMode and process key press however they want

How to handle key press

There are at least 3 ways to handle key press, listed in order of execution:

• gui::Item::onInput - if not redefined calls inputCallback; if handled here, other calls wont be called
• gui::Item::inputCallback - handles any key
• gui::Item::activatedCallback - handles Enter key only
• gui::Item::itemNavigation - handles up,down,left,right if next/previous elements are added for an item

Note: return True when any of callbacks ends processing the whole Items tree

There are 2 set of parameters for key press:

• gui::InputEvent::State - state of key (pressed, released, long released). In general applications handle key releases not presses
• gui::KeyCode - initially parsed key code
• gui::RawKey - raw key code, to be processed in widget based on event i.e. translate pressing key 1 3 times into C in gui::Text mode ABC

How to add key mapping when basic key maps are not enough?

• Key maps are specific key translation mappings i.e. press 1 3 times to get C, press 1 4 times to get A, etc.
• basic key maps are stored in: InputMode, right now there are following InputMode::Modes: [ABC, abc, digit, phone]
• key maps in gui::InputMode are changed in regards of language settings

How to add a new key map

How to add a new key map, i.e. phone:

1. Add new file for your key map: cp image/assets/profiles/template.kprof image/assets/profiles/phone.kprof
2. Change your template accordingly
3. Pin new key map (add it to language support) by adding: "common_kbd_phone": "phone" to at least image/assets/lang/lang_en.json if it will differ per language, prepare one kprof file per language
4. Add new key map to gui::InputMode
   • Add InputMode::Mode enum i.e. InputMode::Mode::phone
   • Add new mode to input mode mapping in InputMode.cpp (same as with other enums)
   • Test newly added mode in: UITestWindow.cpp
   • Test new key map on phone
5. Load key map to phone

Now you can use InputMode::Mode::phone translation in gui::Text widget. This means gui::Text will automatically change text on key press for you, same as in modes InputMode::Mode::phone etc.

Adding new functionalities - visitor pattern in gui::Item

The gui::Item class is compatible with visitor pattern providing double dispatch behaviour. The double dispatch mechanism for all classes in gui::Item's inheritance hierarchy enables easily equipping them with new polymorphic behavior without changing classes themselves.

Structure

Every new functionality to be added to gui::Item hierarchy requires creation of new concrete visitor that publicly inherits from gui::GuiVisitor interface and specifies respective behavior. In order to ensure that a class in gui::Item hierarchy is recognized by its concrete type in ConcreteVisitor::visit(...) method, class must override gui::Item::accept(gui::GuiVisitor &), otherwise it will be resolved as a closest ancestor. On the diagram below both gui::CustomItem1 and gui::CustomItem2 will be resolved as gui::Rect despite existing gui::GuiVisitor::visit(gui::CustomItem2 &) overload and gui::CustomItem1::accept(...) override.

Tree of gui::Item

Each gui::Item object is used as a node to build a UI general tree. That relation can simply be thought of as a tree of dependencies with a node being a parent of zero, one or more other nodes. Concerning the need of a ConcreteVisitors to visit not only the parent but also all its children, gui::ItemTree is an interface class providing abstract interface for implementation of gui::Item tree traversal. The concrete realization of gui::ItemTree is gui::DepthFirstItemTree.

Depth-First tree of gui::Item

gui::DepthFirstItemTree builds tree of parent-children relation for any gui::Item pointed as the root.

The class offers two traverse modes:

• PreOrder - in this mode a parent precedes all its children
• PostOrder - in this mode all children precede their parent

Example

Domain Object Model of gui::Item

Each gui::Item object can be serialized into JSON-formatted stream using gui::Item2JsonSerializer. The serializing class employs dedicated gui::Item2JsonSerializingVisitor, gui::DepthFirstItemTree in PostOrder mode in a sequence flow analogous to the one presented above. Please find an exemplary fragment of DOM serialization output below.

{"Rect": {
    "Active": true, 
    "BorderColor": [0, 0], 
    "Children": [
        {"Label": {
            "Active": true, 
            "BorderColor": [0, 0], 
            "ChildrenCount": 0, 
            "Corners": 240, 
            "DrawArea": [20, 445, 440, 30], 
            "Edges": 0, 
            "FillColor": [15, 15], 
            "Filled": false, 
            "FlatEdges": 0, 
            "Focus": false, 
            "ItemType": 0, 
            "PenFocusWidth": 2, 
            "PenWidth": 1, 
            "TextValue": "Interval Chime", 
            "Visible": true, 
            "WidgetArea": [0, 0, 440, 30], 
            "WidgetMaximumArea": [0, 0, 440, 30], 
            "WidgetMinimumArea": [0, 0, 440, 30], 
            "YapSize": 10, "Yaps": 0}
        },
        {"Label": {...}}
    ], 
    "ChildrenCount": 2, 
    "Corners": 240, 
    "DrawArea": [20, 445, 440, 60], 
    "Edges": 0, 
    "FillColor": [15, 15], 
    "Filled": false, 
    "FlatEdges": 0, 
    "Focus": true, 
    "ItemType": 0, 
    "PenFocusWidth": 2, 
    "PenWidth": 1, 
    "Visible": true, 
    "WidgetArea": [20, 445, 440, 60], 
    "WidgetMaximumArea": [0, 0, 440, 60], 
    "WidgetMinimumArea": [0, 0, 440, 60], 
    "YapSize": 10, "Yaps": 0}
}

Widgets

• Window
• Text