1```eval_rst
2.. include:: /header.rst
3:github_url: |github_link_base|/porting/indev.md
4```
5# Input device interface
6
7## Types of input devices
8
9To 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.**
10
11```c
12lv_disp_drv_register(&disp_drv);
13
14static lv_indev_drv_t indev_drv;
15lv_indev_drv_init(&indev_drv);      /*Basic initialization*/
16indev_drv.type =...                 /*See below.*/
17indev_drv.read_cb =...              /*See below.*/
18/*Register the driver in LVGL and save the created input device object*/
19lv_indev_t * my_indev = lv_indev_drv_register(&indev_drv);
20```
21
22The `type` member can be:
23- `LV_INDEV_TYPE_POINTER` touchpad or mouse
24- `LV_INDEV_TYPE_KEYPAD` keyboard or keypad
25- `LV_INDEV_TYPE_ENCODER` encoder with left/right turn and push options
26- `LV_INDEV_TYPE_BUTTON` external buttons virtually pressing the screen
27
28`read_cb` is a function pointer which will be called periodically to report the current state of an input device.
29
30Visit [Input devices](/overview/indev) to learn more about input devices in general.
31
32###  Touchpad, mouse or any pointer
33Input devices that can click points on the screen belong to this category.
34
35```c
36indev_drv.type = LV_INDEV_TYPE_POINTER;
37indev_drv.read_cb = my_input_read;
38
39...
40
41void my_input_read(lv_indev_drv_t * drv, lv_indev_data_t*data)
42{
43  if(touchpad_pressed) {
44    data->point.x = touchpad_x;
45    data->point.y = touchpad_y;
46    data->state = LV_INDEV_STATE_PRESSED;
47  } else {
48    data->state = LV_INDEV_STATE_RELEASED;
49  }
50}
51```
52
53To set a mouse cursor use `lv_indev_set_cursor(my_indev, &img_cursor)`. (`my_indev` is the return value of `lv_indev_drv_register`)
54
55### Keypad or keyboard
56
57Full keyboards with all the letters or simple keypads with a few navigation buttons belong here.
58
59To use a keyboard/keypad:
60- Register a `read_cb` function with `LV_INDEV_TYPE_KEYPAD` type.
61- 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)`
62- 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`)
63- Use `LV_KEY_...` to navigate among the objects in the group. See `lv_core/lv_group.h` for the available keys.
64
65```c
66indev_drv.type = LV_INDEV_TYPE_KEYPAD;
67indev_drv.read_cb = keyboard_read;
68
69...
70
71void keyboard_read(lv_indev_drv_t * drv, lv_indev_data_t*data){
72  data->key = last_key();            /*Get the last pressed or released key*/
73
74  if(key_pressed()) data->state = LV_INDEV_STATE_PRESSED;
75  else data->state = LV_INDEV_STATE_RELEASED;
76}
77```
78
79### Encoder
80With an encoder you can do the following:
811. Press its button
822. Long-press its button
833. Turn left
844. Turn right
85
86In short, the Encoder input devices work like this:
87- By turning the encoder you can focus on the next/previous object.
88- When you press the encoder on a simple object (like a button), it will be clicked.
89- 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.
90- To leave edit mode, long press the button.
91
92
93To use an *Encoder* (similarly to the *Keypads*) the objects should be added to groups.
94
95
96```c
97indev_drv.type = LV_INDEV_TYPE_ENCODER;
98indev_drv.read_cb = encoder_read;
99
100...
101
102void encoder_read(lv_indev_drv_t * drv, lv_indev_data_t*data){
103  data->enc_diff = enc_get_new_moves();
104
105  if(enc_pressed()) data->state = LV_INDEV_STATE_PRESSED;
106  else data->state = LV_INDEV_STATE_RELEASED;
107}
108```
109
110#### Using buttons with Encoder logic
111In addition to standard encoder behavior, you can also utilize its logic to navigate(focus) and edit widgets using buttons.
112This is especially handy if you have only few buttons available, or you want to use other buttons in addition to encoder wheel.
113
114You need to have 3 buttons available:
115- `LV_KEY_ENTER` will simulate press or pushing of the encoder button
116- `LV_KEY_LEFT` will simulate turning encoder left
117- `LV_KEY_RIGHT` will simulate turning encoder right
118- other keys will be passed to the focused widget
119
120If you hold the keys it will simulate an encoder advance with period specified in `indev_drv.long_press_rep_time`.
121
122```c
123indev_drv.type = LV_INDEV_TYPE_ENCODER;
124indev_drv.read_cb = encoder_with_keys_read;
125
126...
127
128void encoder_with_keys_read(lv_indev_drv_t * drv, lv_indev_data_t*data){
129  data->key = last_key();            /*Get the last pressed or released key*/
130                                     /* use LV_KEY_ENTER for encoder press */
131  if(key_pressed()) data->state = LV_INDEV_STATE_PRESSED;
132  else {
133      data->state = LV_INDEV_STATE_RELEASED;
134      /* Optionally you can also use enc_diff, if you have encoder*/
135      data->enc_diff = enc_get_new_moves();
136  }
137}
138```
139
140### Button
141*Buttons* mean external "hardware" buttons next to the screen which are assigned to specific coordinates of the screen.
142If a button is pressed it will simulate the pressing on the assigned coordinate. (Similarly to a touchpad)
143
144To assign buttons to coordinates use `lv_indev_set_button_points(my_indev, points_array)`.
145`points_array` should look like `const lv_point_t points_array[] = { {12,30},{60,90}, ...}`
146
147``` 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.
148```
149
150```c
151indev_drv.type = LV_INDEV_TYPE_BUTTON;
152indev_drv.read_cb = button_read;
153
154...
155
156void button_read(lv_indev_drv_t * drv, lv_indev_data_t*data){
157    static uint32_t last_btn = 0;   /*Store the last pressed button*/
158    int btn_pr = my_btn_read();     /*Get the ID (0,1,2...) of the pressed button*/
159    if(btn_pr >= 0) {               /*Is there a button press? (E.g. -1 indicated no button was pressed)*/
160       last_btn = btn_pr;           /*Save the ID of the pressed button*/
161       data->state = LV_INDEV_STATE_PRESSED;  /*Set the pressed state*/
162    } else {
163       data->state = LV_INDEV_STATE_RELEASED; /*Set the released state*/
164    }
165
166    data->btn = last_btn;            /*Save the last button*/
167}
168```
169
170## Other features
171
172### Parameters
173
174The default value of the following parameters can be changed in `lv_indev_drv_t`:
175- `scroll_limit` Number of pixels to slide before actually scrolling the object.
176- `scroll_throw`  Scroll throw (momentum) slow-down in [%]. Greater value means faster slow-down.
177- `long_press_time` Press time to send `LV_EVENT_LONG_PRESSED` (in milliseconds)
178- `long_press_rep_time` Interval of sending `LV_EVENT_LONG_PRESSED_REPEAT` (in milliseconds)
179- `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.
180
181### Feedback
182
183Besides `read_cb` a `feedback_cb` callback can be also specified in `lv_indev_drv_t`.
184`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`.
185
186
187### Associating with a display
188Every 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()`).
189The associated display is stored and can be changed in `disp` field of the driver.
190
191### Buffered reading
192By default, LVGL calls `read_cb` periodically. Because of this intermittent polling there is a chance that some user gestures are missed.
193
194To 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.
195Setting the `data->continue_reading` flag will tell LVGL there is more data to read and it should call `read_cb` again.
196
197## Further reading
198
199- [lv_port_indev_template.c](https://github.com/lvgl/lvgl/blob/master/examples/porting/lv_port_indev_template.c) for a template for your own driver.
200- [INdev features](/overview/display) to learn more about higher level input device features.
201
202## API
203
204```eval_rst
205
206.. doxygenfile:: lv_hal_indev.h
207  :project: lvgl
208
209```
210