Input device interface

Types of input devices

To register an input device an lv_indev_drv_t variable has to be initialized. Be sure to register at least one display before you register any input devices.

lv_disp_drv_register(&disp_drv);

static lv_indev_drv_t indev_drv;
lv_indev_drv_init(&indev_drv);      /*Basic initialization*/
indev_drv.type =...                 /*See below.*/
indev_drv.read_cb =...              /*See below.*/
/*Register the driver in LVGL and save the created input device object*/
lv_indev_t * my_indev = lv_indev_drv_register(&indev_drv);

The type member can be:

  • LV_INDEV_TYPE_POINTER touchpad or mouse

  • LV_INDEV_TYPE_KEYPAD keyboard or keypad

  • LV_INDEV_TYPE_ENCODER encoder with left/right turn and push options

  • LV_INDEV_TYPE_BUTTON external buttons virtually pressing the screen

read_cb is a function pointer which will be called periodically to report the current state of an input device.

Visit Input devices to learn more about input devices in general.

Touchpad, mouse or any pointer

Input devices that can click points on the screen belong to this category.

indev_drv.type = LV_INDEV_TYPE_POINTER;
indev_drv.read_cb = my_input_read;

...

void my_input_read(lv_indev_drv_t * drv, lv_indev_data_t*data)
{
  if(touchpad_pressed) {
    data->point.x = touchpad_x;
    data->point.y = touchpad_y;
    data->state = LV_INDEV_STATE_PRESSED;
  } else {
    data->state = LV_INDEV_STATE_RELEASED; 
  }
}

To set a mouse cursor use lv_indev_set_cursor(my_indev, &img_cursor). (my_indev is the return value of lv_indev_drv_register)

Keypad or keyboard

Full keyboards with all the letters or simple keypads with a few navigation buttons belong here.

To use a keyboard/keypad:

  • Register a read_cb function with LV_INDEV_TYPE_KEYPAD type.

  • An object group has to be created: lv_group_t * g = lv_group_create() and objects have to be added to it with lv_group_add_obj(g, obj)

  • The created group has to be assigned to an input device: lv_indev_set_group(my_indev, g) (my_indev is the return value of lv_indev_drv_register)

  • Use LV_KEY_... to navigate among the objects in the group. See lv_core/lv_group.h for the available keys.

indev_drv.type = LV_INDEV_TYPE_KEYPAD;
indev_drv.read_cb = keyboard_read;

...

void keyboard_read(lv_indev_drv_t * drv, lv_indev_data_t*data){
  data->key = last_key();            /*Get the last pressed or released key*/

  if(key_pressed()) data->state = LV_INDEV_STATE_PRESSED;
  else data->state = LV_INDEV_STATE_RELEASED;
}

Encoder

With an encoder you can do the following:

  1. Press its button

  2. Long-press its button

  3. Turn left

  4. Turn right

In short, the Encoder input devices work like this:

  • By turning the encoder you can focus on the next/previous object.

  • When you press the encoder on a simple object (like a button), it will be clicked.

  • If you press the encoder on a complex object (like a list, message box, etc.) the object will go to edit mode whereby you can navigate inside the object by turning the encoder.

  • To leave edit mode, long press the button.

To use an Encoder (similarly to the Keypads) the objects should be added to groups.

indev_drv.type = LV_INDEV_TYPE_ENCODER;
indev_drv.read_cb = encoder_read;

...

void encoder_read(lv_indev_drv_t * drv, lv_indev_data_t*data){
  data->enc_diff = enc_get_new_moves();

  if(enc_pressed()) data->state = LV_INDEV_STATE_PRESSED;
  else data->state = LV_INDEV_STATE_RELEASED;
}

Using buttons with Encoder logic

In addition to standard encoder behavior, you can also utilize its logic to navigate(focus) and edit widgets using buttons. This is especially handy if you have only few buttons available, or you want to use other buttons in addition to encoder wheel.

You need to have 3 buttons available:

  • LV_KEY_ENTER will simulate press or pushing of the encoder button

  • LV_KEY_LEFT will simulate turning encoder left

  • LV_KEY_RIGHT will simulate turning encoder right

  • other keys will be passed to the focused widget

If you hold the keys it will simulate an encoder advance with period specified in indev_drv.long_press_rep_time.

indev_drv.type = LV_INDEV_TYPE_ENCODER;
indev_drv.read_cb = encoder_with_keys_read;

...

void encoder_with_keys_read(lv_indev_drv_t * drv, lv_indev_data_t*data){
  data->key = last_key();            /*Get the last pressed or released key*/
                                     /* use LV_KEY_ENTER for encoder press */
  if(key_pressed()) data->state = LV_INDEV_STATE_PRESSED;
  else {
      data->state = LV_INDEV_STATE_RELEASED;
      /* Optionally you can also use enc_diff, if you have encoder*/
      data->enc_diff = enc_get_new_moves();
  }
}

Button

Buttons mean external "hardware" buttons next to the screen which are assigned to specific coordinates of the screen. If a button is pressed it will simulate the pressing on the assigned coordinate. (Similarly to a touchpad)

To assign buttons to coordinates use lv_indev_set_button_points(my_indev, points_array).
points_array should look like const lv_point_t points_array[] =  { {12,30},{60,90}, ...}

Important

The points_array can't go out of scope. Either declare it as a global variable or as a static variable inside a function.

indev_drv.type = LV_INDEV_TYPE_BUTTON;
indev_drv.read_cb = button_read;

...

void button_read(lv_indev_drv_t * drv, lv_indev_data_t*data){
    static uint32_t last_btn = 0;   /*Store the last pressed button*/
    int btn_pr = my_btn_read();     /*Get the ID (0,1,2...) of the pressed button*/
    if(btn_pr >= 0) {               /*Is there a button press? (E.g. -1 indicated no button was pressed)*/
       last_btn = btn_pr;           /*Save the ID of the pressed button*/
       data->state = LV_INDEV_STATE_PRESSED;  /*Set the pressed state*/
    } else {
       data->state = LV_INDEV_STATE_RELEASED; /*Set the released state*/
    }

    data->btn = last_btn;            /*Save the last button*/
}

Other features

Parameters

The default value of the following parameters can be changed in lv_indev_drv_t:

  • scroll_limit Number of pixels to slide before actually scrolling the object.

  • scroll_throw Scroll throw (momentum) slow-down in [%]. Greater value means faster slow-down.

  • long_press_time Press time to send LV_EVENT_LONG_PRESSED (in milliseconds)

  • long_press_rep_time Interval of sending LV_EVENT_LONG_PRESSED_REPEAT (in milliseconds)

  • read_timer pointer to the lv_timer which reads the input device. Its parameters can be changed by lv_timer_...() functions. LV_INDEV_DEF_READ_PERIOD in lv_conf.h sets the default read period.

Feedback

Besides read_cb a feedback_cb callback can be also specified in lv_indev_drv_t. feedback_cb is called when any type of event is sent by the input devices (independently of its type). This allows generating feedback for the user, e.g. to play a sound on LV_EVENT_CLICKED.

Associating with a display

Every input device is associated with a display. By default, a new input device is added to the last display created or explicitly selected (using lv_disp_set_default()). The associated display is stored and can be changed in disp field of the driver.

Buffered reading

By default, LVGL calls read_cb periodically. Because of this intermittent polling there is a chance that some user gestures are missed.

To solve this you can write an event driven driver for your input device that buffers measured data. In read_cb you can report the buffered data instead of directly reading the input device. Setting the data->continue_reading flag will tell LVGL there is more data to read and it should call read_cb again.

Further reading

API

@description Input Device HAL interface layer header file

Typedefs

typedef struct _lv_indev_drv_t lv_indev_drv_t

Initialized by the user and registered by 'lv_indev_add()'

typedef struct _lv_indev_proc_t _lv_indev_proc_t

Run time data of input devices Internally used by the library, you should not need to touch it.

typedef struct _lv_indev_t lv_indev_t

The main input device descriptor with driver, runtime data ('proc') and some additional information

Enums

enum lv_indev_type_t

Possible input device types

Values:

enumerator LV_INDEV_TYPE_NONE

Uninitialized state

enumerator LV_INDEV_TYPE_POINTER

Touch pad, mouse, external button

enumerator LV_INDEV_TYPE_KEYPAD

Keypad or keyboard

enumerator LV_INDEV_TYPE_BUTTON

External (hardware button) which is assigned to a specific point of the screen

enumerator LV_INDEV_TYPE_ENCODER

Encoder with only Left, Right turn and a Button

enum lv_indev_state_t

States for input devices

Values:

enumerator LV_INDEV_STATE_RELEASED
enumerator LV_INDEV_STATE_PRESSED

Functions

void lv_indev_drv_init(struct _lv_indev_drv_t *driver)

Initialize an input device driver with default values. It is used to surely have known values in the fields and not memory junk. After it you can set the fields.

Parameters

driver -- pointer to driver variable to initialize

lv_indev_t *lv_indev_drv_register(struct _lv_indev_drv_t *driver)

Register an initialized input device driver.

Parameters

driver -- pointer to an initialized 'lv_indev_drv_t' variable (can be local variable)

Returns

pointer to the new input device or NULL on error

void lv_indev_drv_update(lv_indev_t *indev, struct _lv_indev_drv_t *new_drv)

Update the driver in run time.

Parameters
  • indev -- pointer to an input device. (return value of lv_indev_drv_register)

  • new_drv -- pointer to the new driver

void lv_indev_delete(lv_indev_t *indev)

Remove the provided input device. Make sure not to use the provided input device afterwards anymore.

Parameters

indev -- pointer to delete

lv_indev_t *lv_indev_get_next(lv_indev_t *indev)

Get the next input device.

Parameters

indev -- pointer to the current input device. NULL to initialize.

Returns

the next input device or NULL if there are no more. Provide the first input device when the parameter is NULL

void _lv_indev_read(lv_indev_t *indev, lv_indev_data_t *data)

Read data from an input device.

Parameters
  • indev -- pointer to an input device

  • data -- input device will write its data here

struct lv_indev_data_t
#include <lv_hal_indev.h>

Data structure passed to an input driver to fill

Public Members

lv_point_t point

For LV_INDEV_TYPE_POINTER the currently pressed point

uint32_t key

For LV_INDEV_TYPE_KEYPAD the currently pressed key

uint32_t btn_id

For LV_INDEV_TYPE_BUTTON the currently pressed button

int16_t enc_diff

For LV_INDEV_TYPE_ENCODER number of steps since the previous read

lv_indev_state_t state

LV_INDEV_STATE_REL or LV_INDEV_STATE_PR

bool continue_reading

If set to true, the read callback is invoked again

struct _lv_indev_drv_t
#include <lv_hal_indev.h>

Initialized by the user and registered by 'lv_indev_add()'

Public Members

lv_indev_type_t type

< Input device type Function pointer to read input device data.

void (*read_cb)(struct _lv_indev_drv_t *indev_drv, lv_indev_data_t *data)
void (*feedback_cb)(struct _lv_indev_drv_t*, uint8_t)

Called when an action happened on the input device. The second parameter is the event from lv_event_t

void *user_data
struct _lv_disp_t *disp

< Pointer to the assigned display Timer to periodically read the input device

lv_timer_t *read_timer

Number of pixels to slide before actually drag the object

uint8_t scroll_limit

Drag throw slow-down in [%]. Greater value means faster slow-down

uint8_t scroll_throw

At least this difference should be between two points to evaluate as gesture

uint8_t gesture_min_velocity

At least this difference should be to send a gesture

uint8_t gesture_limit

Long press time in milliseconds

uint16_t long_press_time

Repeated trigger period in long press [ms]

uint16_t long_press_repeat_time
struct _lv_indev_proc_t
#include <lv_hal_indev.h>

Run time data of input devices Internally used by the library, you should not need to touch it.

Public Members

lv_indev_state_t state

Current state of the input device.

uint8_t long_pr_sent
uint8_t reset_query
uint8_t disabled
uint8_t wait_until_release
lv_point_t act_point

Current point of input device.

lv_point_t last_point

Last point of input device.

lv_point_t last_raw_point

Last point read from read_cb.

lv_point_t vect

Difference between act_point and last_point.

lv_point_t scroll_sum
lv_point_t scroll_throw_vect
lv_point_t scroll_throw_vect_ori
struct _lv_obj_t *act_obj
struct _lv_obj_t *last_obj
struct _lv_obj_t *scroll_obj
struct _lv_obj_t *last_pressed
lv_area_t scroll_area
lv_point_t gesture_sum
lv_dir_t scroll_dir
lv_dir_t gesture_dir
uint8_t gesture_sent
struct _lv_indev_proc_t::[anonymous]::[anonymous] pointer
lv_indev_state_t last_state
uint32_t last_key
struct _lv_indev_proc_t::[anonymous]::[anonymous] keypad
union _lv_indev_proc_t::[anonymous] types
uint32_t pr_timestamp

Pressed time stamp

uint32_t longpr_rep_timestamp

Long press repeat time stamp

struct _lv_indev_t
#include <lv_hal_indev.h>

The main input device descriptor with driver, runtime data ('proc') and some additional information

Public Members

struct _lv_indev_drv_t *driver
_lv_indev_proc_t proc
struct _lv_obj_t *cursor

Cursor for LV_INPUT_TYPE_POINTER

struct _lv_group_t *group

Keypad destination group

const lv_point_t *btn_points

Array points assigned to the button ()screen will be pressed here by the buttons