Input device interface¶

Types of input devices¶

To register an input device an lv_indev_drv_t variable has to be initialized:

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);

type 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 4 things:

Press its button
Long-press its button
Turn left
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 turning the encoder you can navigate inside the object.
To leave edit mode press long 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 encoder click 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;

...

bool 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();
  }

  return false; /*No buffering now so no more data read*/
}

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 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 from 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 lastly created or the explicitly selected (using lv_disp_set_default()) display. The associated display is stored and can be changed in disp field of the driver.

Buffered reading¶

By default LVGL calls read_cb periodically. This way 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 set the buffered data instead of reading the input device. You can set the data->continue_reading flag to tell that LVGL there is more data to read and it should call the read_cb again.

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 surly have known values in the fields ant 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 a input device. (return value of lv_indev_drv_register)
new_drv -- pointer to the new driver

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 devise or NULL if no more. Give 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¶: Call the read callback until it's set to true

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 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

Input device interface¶

Types of input devices¶

Touchpad, mouse or any pointer¶

Keypad or keyboard¶

Encoder¶

Using buttons with Encoder logic¶

Button¶

Other features¶

Parameters¶

Feedback¶

Associating with a display¶

Buffered reading¶

Further reading¶

API¶