Gravity Forms - Populate Name Field - Setting Field Default Value Directly - Part 1.

functions.php

/**
 * Populate a Gravity Forms Name field.
 * 
 * @param array        $field  Gravity Forms field object
 * @param string|array $name   Name components, pass either a string or array when the 
 *                             nameFormat is 'simple' or an array in all other cases  
 */
function eo_populate_name_field(&$field, $name = array())
{
  if ( !(is_array($field) && ('name' == rgar($field, 'type')) && !empty($name)) )
    return;
  
  $field_id = $field['id'];
  $format = rgar($field, 'nameFormat'); 
  
  if ( is_array($name) )
  {
    $first = sanitize_text_field(rgar($name, 'first'));
    $last  = sanitize_text_field(rgar($name, 'last'));    
  }
  
  switch ($format)
  {
    case 'simple':        
      $default_value = isset($first, $last) ? ($first . ' ' . $last) : $name;
      $default_value = sanitize_text_field($default_value);   
    break;
      
    case 'normal':
      $default_value = array_filter(array
      (
        (strval($field_id . '.3')) => $first,
        (strval($field_id . '.6')) => $last,
      ));
    break;
      
    case 'extended':
      $prefix = sanitize_text_field(rgar($name, 'prefix'));
      $suffix = sanitize_text_field(rgar($name, 'suffix'));
      
      $default_value = array_filter(array
      (
        (strval($field_id . '.2')) => $prefix,
        (strval($field_id . '.3')) => $first,
        (strval($field_id . '.6')) => $last,
        (strval($field_id . '.8')) => $suffix,
      ));        
      
    break;
  }

  if ( !empty($default_value) )
    $field['defaultValue'] = $default_value;
}