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Network / [Solved-ish] Movement Lag on Client

« on: March 04, 2013, 08:29:31 pm »

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Last update 6.21AM 10Mar2013 -8 GMT

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I'm giving a dabble at SFML networking and I have what I think is probably a very basic issue/fundamental misunderstanding on my part.

I have created a server that sends out commands to a client in order to move a rectangle, however the client end is always lagged compared to the server as can be seen here:

I haven't tried implementing UDP yet, and from what I've been reading real time movement should be implemented with UDP (I think most games are using UDP for this type of stuff/TCP for the chat).

Is my understanding correct and I should move to UDP, or should TCP be able to handle something like this?

I can think of one possible way to eliminate this lag. When the key is pressed on the server end have a move left sent and the client will continuously move until a move left end is received.. and this should synch it up better, but I'm wondering if there is a better approach. Another possibility I thought of is just send the exact coords of where the client rectangle should be.

Thanks! Any input/advice is greatly appreciated as always.

main.cpp

//#include "VoIP.hpp"
#include "tcp_issue.hpp"


int main( int argc, char* argv[])
{
    //voip example
    //voipExample();

    if( argc > 2 )
    {

        //tcp/udp issue
        issueServer( argv[1], argv[2] ); //[server,client] [tcp,udp]
    }

    return EXIT_SUCCESS;
}
 

tcp_issue.hpp

#include <SFML/Graphics.hpp>
#include <string>

const float MOVE_SPEED = 70;
const int PORT = 7777;

sf::TcpSocket socket;
sf::UdpSocket usocket;
sf::Mutex globalMutex;

std::string command = "";

bool quit = false;

void tcpServerListen();
void tcpClient();
void tcpSend();

void udpServer();
void udpClient();
void udpSend();

void issueServer( std::string mode, std::string method )
{
    std::cout << "Incoming mode: " << mode << std::endl;
    std::cout << "Incoming method: " << method << std::endl;

    sf::Thread threadServerTCP(&tcpServerListen);
    sf::Thread threadClientTCP(&tcpClient);
    sf::Thread threadServerUDP(&udpServer);
    sf::Thread threadClientUDP(&udpClient);

    if( mode.compare("server") == 0 )
    {
        std::cout << "Starting in server mode.\n";
        if( method.compare("tcp") == 0 )
        {
            std::cout << "Launching server tcp thread\n";
            threadServerTCP.launch();
        }
        else
        {
            std::cout << "Launching server udp thread\n";
            threadServerUDP.launch();
        }
    }
    else
    {
        std::cout << "Starting in client mode.\n";
        if( method.compare("tcp") == 0 )
        {
            std::cout << "Starting tcp client thread.\n";
            threadClientTCP.launch();
        }
        else
        {
            std::cout << "Starting udp client thread.\n";
            threadClientTCP.launch();
        }
    }


    sf::RenderWindow window(sf::VideoMode(800, 600), "SFML Playground");

    sf::Clock Clock;
    sf::Time time;

    sf::RectangleShape rectangle;
    rectangle.setSize(sf::Vector2f(100, 50));
    rectangle.setOutlineColor(sf::Color::Red);
    rectangle.setOutlineThickness(5);
    rectangle.setPosition(10, 20);

    while (window.isOpen())
    {
        sf::Event event;
        while (window.pollEvent(event))
        {
            if (event.type == sf::Event::Closed)
            {
                quit = true;

                if( method.compare("tcp") == 0 )
                    threadClientTCP.wait();
                else
                    threadClientUDP.wait();

                window.close();
            }
            if (event.type == sf::Event::KeyPressed)
            {
            }
        }
        if( mode.compare("server") == 0 )
        {
            if (sf::Keyboard::isKeyPressed(sf::Keyboard::A))
            {
                globalMutex.lock();
                command = "left";
                globalMutex.unlock();

                if( method.compare("tcp") == 0 )
                    tcpSend();
                else
                    udpSend();

                rectangle.move(-1*MOVE_SPEED*time.asSeconds(),0);
            }

            if (sf::Keyboard::isKeyPressed(sf::Keyboard::S))
            {
                globalMutex.lock();
                command = "down";
                globalMutex.unlock();

                if( method.compare("tcp") == 0 )
                    tcpSend();
                else
                    udpSend();

                rectangle.move(0,1*MOVE_SPEED*time.asSeconds());
            }

            if (sf::Keyboard::isKeyPressed(sf::Keyboard::D))
            {
                globalMutex.lock();
                command = "right";
                globalMutex.unlock();

                if( method.compare("tcp") == 0 )
                    tcpSend();
                else
                    udpSend();

                rectangle.move(1*MOVE_SPEED*time.asSeconds(),0);
            }

            if (sf::Keyboard::isKeyPressed(sf::Keyboard::W))
            {
                globalMutex.lock();
                command = "up";
                globalMutex.unlock();

                if( method.compare("tcp") == 0 )
                    tcpSend();
                else
                    udpSend();

                rectangle.move(0,-1*MOVE_SPEED*time.asSeconds());
            }
        }
        else
        {
            if (command.compare("left") == 0)
            {
                rectangle.move(-1*MOVE_SPEED*time.asSeconds(),0);

                globalMutex.lock();
                command = "";
                globalMutex.unlock();
            }

            if (command.compare("down")  == 0 )
            {
                rectangle.move(0,1*MOVE_SPEED*time.asSeconds());

                globalMutex.lock();
                command = "";
                globalMutex.unlock();
            }

            if (command.compare("right")  == 0 )
            {
                rectangle.move(1*MOVE_SPEED*time.asSeconds(),0);

                globalMutex.lock();
                command = "";
                globalMutex.unlock();
            }

            if (command.compare("up")  == 0 )
            {
                rectangle.move(0,-1*MOVE_SPEED*time.asSeconds());

                globalMutex.lock();
                command = "";
                globalMutex.unlock();
            }

        }


        window.draw( rectangle );
        window.display();
        window.clear();

        time = Clock.restart();
    }
}

void tcpSend()
{
        sf::Packet packetSend;
        globalMutex.lock();
        packetSend << command;
        globalMutex.unlock();
        command = "";
        socket.send(packetSend);
}

void udpSend()
{
}

void tcpServerListen()
{
    sf::TcpListener listener;
    listener.listen(PORT);
    listener.accept(socket);
    std::cout << "New client connected: " << socket.getRemoteAddress() << std::endl;
}

void udpServer()
{
}


void udpClient()
{
}


void tcpClient()
{
        if(socket.connect("127.0.0.1", PORT) == sf::Socket::Done)
                std::cout << "Connected\n";
    else
        std::cout << "FAILURE\n";

    while( !quit )
    {
                std::string msg;
                sf::Packet packetReceive;
                socket.receive(packetReceive);

                packetReceive >> msg;

                if( !msg.empty() )
                {
            std::cout << "Command Received: " << msg << std::endl;
            globalMutex.lock();
            command = msg;
            globalMutex.unlock();
                }
    }
}
 

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