evdev

The Linux event device (evdev) is a hardware-independent API that gives access to input events from, for example, a mouse or touchscreen. It is exposed via the Linux device file system interface.

Overview

The Linux event device (evdev) is a hardware-independent API that gives access to input events from, for example, a mouse or touchscreen. It is exposed via the Linux device file system interface.

Prerequisites

Your system has an input device configured (usually under /dev/input/ such as /dev/input/event0).

Configuring the driver

Enable the Linux LVGL evdev driver support in lv_conf.h.

#define LV_USE_EVDEV 1

Usage

To set up an event input, first create an input device with lv_edev_create setting it to the correct Linux event device. Then link this to the LVGL display with lv_indev_set_display.

lv_indev_t *touch = lv_evdev_create(LV_INDEV_TYPE_POINTER, "/dev/input/event0");
lv_indev_set_display(touch, disp);

Ensure that an lv_display_t object is already created for disp. An example for this is shown below, using the Linux framebuffer driver.

lv_display_t * disp = lv_linux_fbdev_create();
lv_linux_fbdev_set_file(disp, "/dev/fb0");

Locating your input device

If you can't determine your input device, first run

$cat /proc/bus/input/devices

This should show input devices and there will be entries with the word event which give a clue as to the device to use eg. event1 would be /dev/input/event1.

You can use evtest to show data from that event source to see if it is actually the one you want.

Try:

$evtest /dev/input/event1 replacing eventX with your event device from above.

Automatic input device discovery

There is support for automatically finding and adding input devices in /dev/input/. New devices will automatically be added when they are connected. To enable this feature, you can simply call lv_evdev_discovery_start(NULL, NULL).

You may want to react to a new device being added so that a cursor image can be applied, for example. You can provide a callback function which will be called when a new device is added.

#include "lvgl/src/core/lv_global.h"

static void indev_deleted_cb(lv_event_t * e)
{
    if(LV_GLOBAL_DEFAULT()->deinit_in_progress) return;
    lv_obj_t * cursor_obj = lv_event_get_user_data(e)
    lv_obj_delete(cursor_obj);
}

static void discovery_cb(lv_indev_t * indev, lv_evdev_type_t type, void * user_data)
{
    LV_LOG_USER("new '%s' device discovered", type == LV_EVDEV_TYPE_REL ? "REL" :
                                              type == LV_EVDEV_TYPE_ABS ? "ABS" :
                                              type == LV_EVDEV_TYPE_KEY ? "KEY" :
                                              "unknown");

    if(type == LV_EVDEV_TYPE_REL) {
        LV_IMAGE_DECLARE(mouse_cursor_icon);
        lv_obj_t * cursor_obj = lv_image_create(lv_screen_active());
        lv_image_set_src(cursor_obj, &mouse_cursor_icon);
        lv_indev_set_cursor(indev, cursor_obj);
        lv_indev_add_event_cb(indev, indev_deleted_cb, LV_EVENT_DELETE, cursor_obj);
    }
}

int main()
{
    /* ... */
    lv_evdev_discovery_start(discovery_cb, NULL);
    /* ... */
}

At the time of writing, this feature is not supported in BSD.