LiTE Architecture

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LiTE stands for LiTE is a Toolbox Engine. Its role is to facilitate the functions of DirectFB so that a toolbox could be written on top of DirectFB with less effort. As such LiTE has abstractions for the underlying graphics and event systems.


Contents

LiteBox and Graphics Surfaces

An important abstraction is the LiteBox. It is a low-level view that is tied to a so called sub-surface of a DirectFB surface.

When a LiTE application initializes itself, as part of that process, a window is most likely created. The window has a DirectFB surface to store the actual pixel content and acts as a top level LiteBox. Any LiteBox created as a child will create a sub-surface. It's basically just another handle (think of a graphics context) to the same surface, so it's using the existing pixel buffer, but with a translated origin, limited clipping area, separate render state etc.

Two examples where LiteBox could be used are window decorations and placing views such as widgets into the main window. The current theme system in LiTE is cutting out the top/bottom, left and right parts of a window into separate LiteBox entries, and these could be manipulated, such as placing a texture into these areas, adding strings to the top part (as in window titles), or a possible close icon in the top-right corner.

LiteBox and Events

LiteBox entries are serviced events via a main event Buffer. This is done by starting the LiTE event loop from the LiteWindow APIs. Inside this event loop, the event is parsed. In the case of DFBWindow events, the right LiteBox is triggered by finding out which box is the innermost in a hierarchy of boxes installed inside each other. Based on that the right box will be called, and special callbacks for various events will trigger.

Examples of such callbacks are OnMouseEnter and OnMouseLeave. When the mouse entered or is leaving this box area, then one or the other of the callbacks is triggered. By default most of these callbacks are not doing anything, they are mostly used for derived widgets.


LiteBox Child/Parent Relationships

LiteBox has a notion of parent/child inheritance. When a LiteBox is created, its parent is defined, and the parent will store this new child in its child array. When the LiteBox is deleted (lite_destroy_box()), then the parent array is updated and the entry is removed. Also, as part of deleting this box, it will also call all its child LiteBox entries and call their lite_destroy_box() calls, ensuring that each level is properly deleted.

LiteBox Inheritance

A higher-level widget is usually created by having as its first entry in the data structure a LiteBox. This makes it possible to cast it into a LiteBox and use the LiTE APIs related to the LiteBox.


LiTE Callback Methods

LiteBox has a set of function callbacks that could be overwritten by accessing these public slots (box.h has the 'LiteBox' structure exported). Examples of such callbacks are: OnKeyUp, OnKeyDown, Draw, Destroy, etcetera.

If a compound widget or another part wants to override the default style (of which most do nothing), it accesses the function pointer, calls its own function, and possible calls the original function before or after its function has been triggered. This makes it possible to make adornment to the actual widget, or even implement a new behavior. Think of this as very similar to member functions in C.


Compound Widgets

The LiteBox base widgets are very primitive, each one is doing one specific job, for instance LiteLabel will display a text label, and LiteButton will use a set of bitmaps to show button states and activate the states.

Complex widgets are built by creating a compound widget that contains lower-level widgets. As an example, a checkbox could be built by including a LiteLabel that has four states related to what the checkbox icon should look like in various states, and a LiteLabel that draws a text string next to the LiteButton showing the checkbox icon. Both of these two primitives are inside a parent LiteBox that occupies a specific area in the surface. Any control of this API is done via a specific API that controls this compound structure.


LiteWindow

LiteWindow takes care of events and global functions. A lot of the underlying event state is recorded in this structure. Examples of event state are: opacity level, the underlying IDirectFBSurface and the IDirectFBWindow, window ID. See the window.h for more information.

A LiteWindow is initialized and then its event loop is started. If there are multiple windows, they all share the initial window’s event buffer. However, just an initial lite_window_event_loop() is triggered.


LiTE Base Widgets

LiTE has a set of basic widgets that could be used standalone, or for building more complex widgets.

One of the more versatile widgets is the LiteButton widget. It knows of four discrete states:

   * Normal - normal drawing of the button
   * Pressed - the button is pressed
   * Hilite - the button is hilited (moving over with a mouse)
   * Disabled - the button is disabled 

You could provide four specific images for each of the state, and the LiTE framework will issue the right one to be drawn based on the incoming mouse events, or by setting the LiteButton into a specific state.

LiteLabel is used for drawing text in a known location. It handled UTF-8 Unicode and arbitrary fonts.

LiteImage is a quick way to load images into a location. However, for button purposes LiteButton should be used, even if with the magic of LiteBox callbacks button behavior could be introduced.

LiteSlider is intended to build slider-like widgets.

LiteAnimation is a primitive widget for building a sequence of images that are triggered.

LiteTextLine is a single line text editing field.

LiTE Initialization

The code that is called when LiTE is initialized is in lite.c. lite_open will initialize DirectFB, and get access to the DFB display layer, after this the default font and cursor is initialized. You could always get access to the IDirectFB interface via lite_get_dfb_interface().

Most of the interesting window initialization is happening inside lite_init_window. This is where access to the surface is done, setting up the window with various DirectFB flags, etcetera.


LiTE Window Updating

The window content updating is done by issuing a lite_update_box() call that queues a repaint for a certain region of a LiteBox. This LiTE call is to be triggered whenever there's a need to update a box's content. The event loop will execute queued updates.

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