lvgl/docs/get-started/quick-overview.rst

.. _quick-overview:

==============
Quick overview
==============

Here you can learn the most important things about LVGL. You should read
this first to get a general impression and read the detailed
:ref:`porting` and :ref:`overview` sections
after that.

Get started in a simulator
--------------------------

Instead of porting LVGL to embedded hardware straight away, it's highly
recommended to get started in a simulator first.

LVGL is ported to many IDEs to be sure you will find your favorite one.
Go to the :ref:`simulator` section to get ready-to-use projects that can be run
on your PC. This way you can save the time of porting for now and get some
experience with LVGL immediately.

Add LVGL into your project
--------------------------

If you would rather try LVGL on your own project follow these steps:

-  `Download <https://github.com/lvgl/lvgl/archive/master.zip>`__ or
   clone the library from GitHub with ``git clone https://github.com/lvgl/lvgl.git``.
-  Copy the ``lvgl`` folder into your project.
-  Copy ``lvgl/lv_conf_template.h`` as ``lv_conf.h`` next to the
   ``lvgl`` folder, change the first ``#if 0`` to ``1`` to enable the
   file's content and set the :c:macro:`LV_COLOR_DEPTH` defines.
-  Include ``lvgl/lvgl.h`` in files where you need to use LVGL related functions.
-  Call :cpp:expr:`lv_tick_inc(x)` every ``x`` milliseconds in a Timer or Task
   (``x`` should be between 1 and 10). It is required for the internal
   timing of LVGL. Alternatively, register a ``tick_get_cb`` with
   :cpp:func:`lv_tick_set_cb` so that LVGL can retrieve the current time directly.
-  Call :cpp:func:`lv_init`
-  Create a draw buffer: LVGL will render the graphics here first, and
   send the rendered image to the display. The buffer size can be set
   freely but 1/10 screen size is a good starting point.

.. code:: c

   static lv_disp_draw_buf_t draw_buf;
   static lv_color_t buf1[MY_DISP_HOR_RES * MY_DISP_VER_RES / 10];                        /*Declare a buffer for 1/10 screen size*/
   lv_disp_draw_buf_init(&draw_buf, buf1, NULL, MY_DISP_HOR_RES * MY_DISP_VER_RES / 10);  /*Initialize the display buffer.*/

-  Implement and register a function which can copy the rendered image
   to an area of your display:

.. code:: c

   static lv_disp_t disp_drv;        /*Descriptor of a display driver*/
   lv_disp_drv_init(&disp_drv);          /*Basic initialization*/
   disp_drv.flush_cb = my_disp_flush;    /*Set your driver function*/
   disp_drv.draw_buf = &draw_buf;        /*Assign the buffer to the display*/
   disp_drv.hor_res = MY_DISP_HOR_RES;   /*Set the horizontal resolution of the display*/
   disp_drv.ver_res = MY_DISP_VER_RES;   /*Set the vertical resolution of the display*/
   lv_disp_drv_register(&disp_drv);      /*Finally register the driver*/

   void my_disp_flush(lv_disp_t * disp, const lv_area_t * area, lv_color_t * color_p)
   {
       int32_t x, y;
       /*It's a very slow but simple implementation.
        *`set_pixel` needs to be written by you to a set pixel on the screen*/
       for(y = area->y1; y <= area->y2; y++) {
           for(x = area->x1; x <= area->x2; x++) {
               set_pixel(x, y, *color_p);
               color_p++;
           }
       }

       lv_disp_flush_ready(disp);         /* Indicate you are ready with the flushing*/
   }

-  Implement and register a function which can read an input device.
   E.g. for a touchpad:

.. code:: c

   static lv_indev_t indev_drv;           /*Descriptor of a input device driver*/
   lv_indev_drv_init(&indev_drv);             /*Basic initialization*/
   indev_drv.type = LV_INDEV_TYPE_POINTER;    /*Touch pad is a pointer-like device*/
   indev_drv.read_cb = my_touchpad_read;      /*Set your driver function*/
   lv_indev_drv_register(&indev_drv);         /*Finally register the driver*/

   void my_touchpad_read(lv_indev_drv_t * indev_drv, lv_indev_data_t * data)
   {
       /*`touchpad_is_pressed` and `touchpad_get_xy` needs to be implemented by you*/
       if(touchpad_is_pressed()) {
         data->state = LV_INDEV_STATE_PRESSED;
         touchpad_get_xy(&data->point.x, &data->point.y);
       } else {
         data->state = LV_INDEV_STATE_RELEASED;
       }

   }

-  Call :cpp:func:`lv_timer_handler` periodically every few milliseconds in
   the main ``while(1)`` loop or in an operating system task. It will
   redraw the screen if required, handle input devices, animation etc.

For a more detailed guide go to the :ref:`porting`
section.

Learn the basics
----------------

Widgets
~~~~~~~

The graphical elements like Buttons, Labels, Sliders, Charts etc. are
called objects or widgets. Go to :ref:`widgets` to see the
full list of available widgets.

Every object has a parent object where it is created. For example, if a
label is created on a button, the button is the parent of label.

The child object moves with the parent and if the parent is deleted the
children will be deleted too.

Children can be visible only within their parent's bounding area. In
other words, the parts of the children outside the parent are clipped.

A Screen is the "root" parent. You can have any number of screens.

To get the current screen call :cpp:func:`lv_screen_active`, and to load a screen
use :cpp:expr:`lv_screen_load(scr1)`.

You can create a new object with ``lv_<type>_create(parent)``. It will
return an :cpp:type:`lv_obj_t` ``*`` variable that can be used as a reference to the
object to set its parameters.

For example:

.. code:: c

   lv_obj_t * slider1 = lv_slider_create(lv_screen_active());

To set some basic attributes ``lv_obj_set_<parameter_name>(obj, <value>)`` functions can be used. For
example:

.. code:: c

   lv_obj_set_x(btn1, 30);
   lv_obj_set_y(btn1, 10);
   lv_obj_set_size(btn1, 200, 50);

Along with the basic attributes, widgets can have type specific
parameters which are set by ``lv_<widget_type>_set_<parameter_name>(obj, <value>)`` functions. For
example:

.. code:: c

   lv_slider_set_value(slider1, 70, LV_ANIM_ON);

To see the full API visit the documentation of the widgets or the
related header file
(e.g. `lvgl/src/widgets/slider/lv_slider.h <https://github.com/lvgl/lvgl/blob/master/src/widgets/slider/lv_slider.h>`__).

Events
~~~~~~

Events are used to inform the user that something has happened with an
object. You can assign one or more callbacks to an object which will be
called if the object is clicked, released, dragged, being deleted, etc.

A callback is assigned like this:

.. code:: c

   lv_obj_add_event(btn, btn_event_cb, LV_EVENT_CLICKED, NULL); /*Assign a callback to the button*/

   ...

   void btn_event_cb(lv_event_t * e)
   {
       printf("Clicked\n");
   }

:cpp:enumerator:`LV_EVENT_ALL` can be used instead of :cpp:enumerator:`LV_EVENT_CLICKED` to invoke
the callback for any event.

From :cpp:expr:`lv_event_t * e` the current event code can be retrieved with:

.. code:: c

   lv_event_code_t code = lv_event_get_code(e);

The object that triggered the event can be retrieved with:

.. code:: c

   lv_obj_t * obj = lv_event_get_target(e);

To learn all features of the events go to the :ref:`events` section.

Parts
~~~~~

Widgets might be built from one or more *parts*. For example, a button
has only one part called :cpp:enumerator:`LV_PART_MAIN`. However, a
:ref:`slider` has :cpp:enumerator:`LV_PART_MAIN`, :cpp:enumerator:`LV_PART_INDICATOR`
and :cpp:enumerator:`LV_PART_KNOB`.

By using parts you can apply different styles to sub-elements of a
widget. (See below)

Read the widgets' documentation to learn which parts each uses.

States
~~~~~~

LVGL objects can be in a combination of the following states:

- :cpp:enumerator:`LV_STATE_DEFAULT`: Normal, released state
- :cpp:enumerator:`LV_STATE_CHECKED`: Toggled or checked state
- :cpp:enumerator:`LV_STATE_FOCUSED`: Focused via keypad or encoder or clicked via touchpad/mouse
- :cpp:enumerator:`LV_STATE_FOCUS_KEY`: Focused via keypad or encoder but not via touchpad/mouse
- :cpp:enumerator:`LV_STATE_EDITED`: Edit by an encoder
- :cpp:enumerator:`LV_STATE_HOVERED`: Hovered by mouse (not supported now)
- :cpp:enumerator:`LV_STATE_PRESSED`: Being pressed
- :cpp:enumerator:`LV_STATE_SCROLLED`: Being scrolled
- :cpp:enumerator:`LV_STATE_DISABLED`: Disabled

For example, if you press an object it will automatically go to the
:cpp:enumerator:`LV_STATE_FOCUSED` and :cpp:enumerator:`LV_STATE_PRESSED` states and when you
release it the :cpp:enumerator:`LV_STATE_PRESSED` state will be removed while focus
remains active.

To check if an object is in a given state use
``lv_obj_has_state(obj, LV_STATE_...)``. It will return ``true`` if the
object is currently in that state.

To manually add or remove states use:

.. code:: c

   lv_obj_add_state(obj, LV_STATE_...);
   lv_obj_remove_state(obj, LV_STATE_...);

Styles
~~~~~~

A style instance contains properties such as background color, border
width, font, etc. that describe the appearance of objects.

Styles are represented with :cpp:struct:`lv_style_t` variables. Only their pointer
is saved in the objects so they need to be defined as static or global.
Before using a style it needs to be initialized with
:cpp:expr:`lv_style_init(&style1)`. After that, properties can be added to
configure the style. For example:

.. code:: c

   static lv_style_t style1;
   lv_style_init(&style1);
   lv_style_set_bg_color(&style1, lv_color_hex(0xa03080))
   lv_style_set_border_width(&style1, 2))

See the full list of properties here :ref:`style_properties`.

Styles are assigned using the ORed combination of an object's part and
state. For example to use this style on the slider's indicator when the
slider is pressed:

.. code:: c

   lv_obj_add_style(slider1, &style1, LV_PART_INDICATOR | LV_STATE_PRESSED);

If the *part* is :cpp:enumerator:`LV_PART_MAIN` it can be omitted:

.. code:: c

   lv_obj_add_style(btn1, &style1, LV_STATE_PRESSED); /*Equal to LV_PART_MAIN | LV_STATE_PRESSED*/

Similarly, :cpp:enumerator:`LV_STATE_DEFAULT` can be omitted too:

.. code:: c

   lv_obj_add_style(slider1, &style1, LV_PART_INDICATOR); /*Equal to LV_PART_INDICATOR | LV_STATE_DEFAULT*/

For :cpp:enumerator:`LV_STATE_DEFAULT` and :cpp:enumerator:`LV_PART_MAIN` simply write ``0``:

.. code:: c

   lv_obj_add_style(btn1, &style1, 0); /*Equal to LV_PART_MAIN | LV_STATE_DEFAULT*/

Styles can be cascaded (similarly to CSS). It means you can add more
styles to a part of an object. For example ``style_btn`` can set a
default button appearance, and ``style_btn_red`` can overwrite the
background color to make the button red:

.. code:: c

   lv_obj_add_style(btn1, &style_btn, 0);
   lv_obj_add_style(btn1, &style1_btn_red, 0);

If a property is not set on for the current state, the style with
:cpp:enumerator:`LV_STATE_DEFAULT` will be used. A default value is used if the
property is not defined in the default state.

Some properties (typically the text-related ones) can be inherited. This
means if a property is not set in an object it will be searched for in
its parents too. For example, you can set the font once in the screen's
style and all text on that screen will inherit it by default.

Local style properties also can be added to objects. This creates a
style which resides inside the object and is used only by the object:

.. code:: c

   lv_obj_set_style_bg_color(slider1, lv_color_hex(0x2080bb), LV_PART_INDICATOR | LV_STATE_PRESSED);

To learn all the features of styles see the :ref:`styles` section.

Themes
~~~~~~

Themes are the default styles for objects. Styles from a theme are
applied automatically when objects are created.

The theme for your application is a compile time configuration set in
``lv_conf.h``.

Examples
--------

.. include:: ../examples/get_started/index.rst

Micropython
-----------

Learn more about :ref:`micropython`.

.. code:: python

   import lvgl as lv

   # Create a Button and a Label
   scr = lv.obj()
   btn = lv.btn(scr)
   btn.align(lv.screen_active(), lv.ALIGN.CENTER, 0, 0)
   label = lv.label(btn)
   label.set_text("Button")

   # Load the screen
   lv.screen_load(scr)