in src/libguac/protocol.c [320:345]
int guac_protocol_send_cfill(guac_socket* socket,
guac_composite_mode mode, const guac_layer* layer,
int r, int g, int b, int a) {
int ret_val;
guac_socket_instruction_begin(socket);
ret_val =
guac_socket_write_string(socket, "5.cfill,")
|| __guac_socket_write_length_int(socket, mode)
|| guac_socket_write_string(socket, ",")
|| __guac_socket_write_length_int(socket, layer->index)
|| guac_socket_write_string(socket, ",")
|| __guac_socket_write_length_int(socket, r)
|| guac_socket_write_string(socket, ",")
|| __guac_socket_write_length_int(socket, g)
|| guac_socket_write_string(socket, ",")
|| __guac_socket_write_length_int(socket, b)
|| guac_socket_write_string(socket, ",")
|| __guac_socket_write_length_int(socket, a)
|| guac_socket_write_string(socket, ";");
guac_socket_instruction_end(socket);
return ret_val;
}