Logging

LittlevGL has built-in log module to inform the user about what is happening in the library.

Log level

To enable logging, set LV_USE_LOG  1 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 issue, when the system may fail

  • LV_LOG_LEVEL_NONE Do not log anything

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

Logging with printf

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

Custom log function

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 * file, int line, const char * dsc)
{
  /*Send the logs via serial port*/
  if(level == LV_LOG_LEVEL_ERROR) serial_send("ERROR: ");
  if(level == LV_LOG_LEVEL_WARN)  serial_send("WARNING: ");
  if(level == LV_LOG_LEVEL_INFO)  serial_send("INFO: ");
  if(level == LV_LOG_LEVEL_TRACE) serial_send("TRACE: ");

  serial_send("File: ");
  serial_send(file);

  char line_str[8];
  sprintf(line_str,"%d", line);
  serial_send("#");
  serial_send(line_str);

  serial_send(": ");
  serial_send(dsc);
  serial_send("\n");
}

...


lv_log_register_print_cb(my_log_cb);

Add logs

You can also use the log module via the LV_LOG_TRACE/INFO/WARN/ERROR(description) functions.