Logging

LVGL has a built-in Log module to inform the user about what is happening in the library.

Log Level

To enable logging, set LV_USE_LOG in lv_conf.h and set LV_LOG_LEVEL to one of the following values:

LV_LOG_LEVEL_TRACE: A lot of logs to give detailed information
LV_LOG_LEVEL_INFO: Log important events
LV_LOG_LEVEL_WARN: Log if something unwanted happened but didn't cause a problem
LV_LOG_LEVEL_ERROR: Only critical issues, where the system may fail
LV_LOG_LEVEL_USER: Only user messages
LV_LOG_LEVEL_NONE: Do not log anything

The events which have a higher level than the set log level will be logged as well. E.g. if you LV_LOG_LEVEL_WARN, errors will be also logged.

If your system supports printf, you just need to enable LV_LOG_PRINTF in lv_conf.h to send the logs with printf.

If you can't use printf or want to use a custom function to log, you can register a "logger" callback with lv_log_register_print_cb().

For example:

void my_log_cb(lv_log_level_t level, const char * buf)
{
  serial_send(buf, strlen(buf));
}

...


lv_log_register_print_cb(my_log_cb);

You can also use the log module via the LV_LOG_TRACE/INFO/WARN/ERROR/USER(text) or LV_LOG(text) functions. Here:

LV_LOG_TRACE/INFO/WARN/ERROR/USER(text) append the following information to your text
Log Level
__FILE__
__LINE__
__func__
LV_LOG(text) is similar to LV_LOG_USER but has no extra information attached.