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Add an example of using Enet with Allegro.
This should help address questions about why Allegro does not include its own networking code. The example comes in two parts: ex_enet_client and ex_enet_server. The example coordinates movement between circles each controlled by a separate client. The clients send changes in movement direction to the server and rely on the server as an authoritative source of their positions.
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‎examples/CMakeLists.txt‎

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@@ -245,6 +245,14 @@ if(WANT_CURL_EXAMPLE)
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endif(CURL_FOUND)
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endif(WANT_CURL_EXAMPLE)
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# The enet example won't compile if the enet library isn't available.
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# This example isn't important so it's disabled by default to prevent problems.
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option(WANT_ENET_EXAMPLE "Build ex_enet example" off)
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if(WANT_ENET_EXAMPLE)
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example(ex_enet_client -lenet ${PRIM})
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example(ex_enet_server -lenet)
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endif(WANT_ENET_EXAMPLE)
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# example(ex_ogre3d ex_ogre3d.cpp)
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# include_directories(/usr/include/OGRE)
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# target_link_libraries(ex_ogre3d OgreMain)

‎examples/enet_common.h‎

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#ifndef ENET_COMMON_H
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#define ENET_COMMON_H
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#include <allegro5/allegro.h>
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#define SCREEN_W 640
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#define SCREEN_H 480
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#define FPS 30 // framerate
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#define PLAYER_SIZE 16 // radius of player circle
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#define PLAYER_SPEED 200 // movement rate of player in pixels/sec
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#define MAX_PLAYER_COUNT 32
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#define DEFAULT_PORT 9234
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typedef enum
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{
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PLAYER_JOIN,
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PLAYER_LEAVE,
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POSITION_UPDATE,
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} MESSAGE_TYPE;
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// message sent from client to server
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typedef struct
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{
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int x; // requested x movement (-1, 0, or 1)
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int y; // requested y movement (-1, 0, or 1)
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} ClientMessage;
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// message sent from server to client
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typedef struct
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{
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int player_id;
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MESSAGE_TYPE type;
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int x; // current position (x)
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int y; // current position (y)
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ALLEGRO_COLOR color; // valid when type == PLAYER_JOIN
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} ServerMessage;
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// storage for all players
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struct
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{
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bool active;
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int x, y; // current position
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int dx, dy; // direction of movemnt
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ALLEGRO_COLOR color;
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} players[MAX_PLAYER_COUNT];
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#endif

‎examples/ex_enet_client.c‎

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/* Simple networked game example using ENet (http://enet.bespin.org/).
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*
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* You will need enet installed to run this demo.
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*
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* This example is based on http://enet.bespin.org/Tutorial.html
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*
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* To try this example, first run ex_enet_server.
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* Then start multiple instances of ex_enet_client.
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <enet/enet.h>
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#include "allegro5/allegro.h"
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#include "allegro5/allegro_primitives.h"
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#include "common.c"
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#include "enet_common.h"
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static ENetHost* create_client(void)
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{
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ENetHost * client;
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client = enet_host_create(NULL /* create a client host */,
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1 /* only allow 1 outgoing connection */,
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2 /* allow up 2 channels to be used, 0 and 1 */,
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57600 / 8 /* 56K modem with 56 Kbps downstream bandwidth */,
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14400 / 8 /* 56K modem with 14 Kbps upstream bandwidth */);
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if (client == NULL)
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abort_example("Client: Failed to create the client.\n");
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return client;
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}
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static void disconnect_client(ENetHost *client, ENetPeer *server)
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{
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enet_peer_disconnect(server, 0);
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/* Allow up to 3 seconds for the disconnect to succeed
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* and drop any packets received packets.
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*/
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ENetEvent event;
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while (enet_host_service (client, &event, 3000) > 0) {
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switch (event.type) {
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case ENET_EVENT_TYPE_RECEIVE:
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enet_packet_destroy(event.packet);
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break;
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case ENET_EVENT_TYPE_DISCONNECT:
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puts("Client: Disconnect succeeded.");
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return;
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case ENET_EVENT_TYPE_NONE:
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case ENET_EVENT_TYPE_CONNECT:
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break;
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}
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}
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// failed to disconnect gracefully, force the connection closed
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enet_peer_reset(server);
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}
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static ENetPeer* connect_client(ENetHost *client, int port)
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{
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ENetAddress address;
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ENetEvent event;
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ENetPeer *server;
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enet_address_set_host(&address, "localhost");
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address.port = port;
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/* Initiate the connection, allocating the two channels 0 and 1. */
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server = enet_host_connect(client, & address, 2, 0);
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if (server == NULL)
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abort_example("Client: No available peers for initiating an ENet connection.\n");
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/* Wait up to 5 seconds for the connection attempt to succeed. */
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if (enet_host_service(client, & event, 5000) > 0 &&
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event.type == ENET_EVENT_TYPE_CONNECT)
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{
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printf("Client: Connected to %x:%u.\n",
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event.peer->address.host,
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event.peer->address.port);
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}
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else
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{
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/* Either the 5 seconds are up or a disconnect event was */
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/* received. Reset the peer in the event the 5 seconds */
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/* had run out without any significant event. */
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enet_peer_reset(server);
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abort_example("Client: Connection to server failed.");
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}
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return server;
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}
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static void send_receive(ENetHost *client)
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{
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ENetEvent event;
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ServerMessage *msg;
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// Check if we have any queued incoming messages, but do not wait otherwise.
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// This also sends outgoing messages queued with enet_peer_send.
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while (enet_host_service(client, &event, 0) > 0) {
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// clients only care about incoming packets, they will not receive
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// connect/disconnect events.
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if (event.type == ENET_EVENT_TYPE_RECEIVE) {
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msg = (ServerMessage*)event.packet->data;
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switch (msg->type) {
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case POSITION_UPDATE:
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players[msg->player_id].x = msg->x;
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players[msg->player_id].y = msg->y;
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break;
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case PLAYER_JOIN:
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printf("Client: player #%d joined\n", msg->player_id);
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players[msg->player_id].active = true;
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players[msg->player_id].x = msg->x;
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players[msg->player_id].y = msg->y;
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players[msg->player_id].color = msg->color;
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break;
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case PLAYER_LEAVE:
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printf("Client: player #%d left\n", msg->player_id);
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players[msg->player_id].active = false;
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break;
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}
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/* Clean up the packet now that we're done using it. */
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enet_packet_destroy(event.packet);
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}
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}
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}
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int main(int argc, char **argv)
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{
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ALLEGRO_DISPLAY *display;
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ALLEGRO_TIMER *timer;
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ALLEGRO_EVENT_QUEUE *queue;
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ALLEGRO_EVENT event;
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ENetHost *client;
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ENetPeer *server;
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bool update = true; // when true, update positions and render
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bool done = false; // when true, client exits
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int dx = 0, dy = 0; // movement direction
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int port = DEFAULT_PORT;
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if (argc == 2) {
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port = atoi(argv[1]);
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}
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else if (argc > 2)
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abort_example("Usage: %s [portnum]", argv[0]);
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// --- allegro setup ---
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if (!al_init())
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abort_example("Could not init Allegro.\n");
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init_platform_specific();
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al_install_keyboard();
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al_init_primitives_addon();
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// Create a new display that we can render the image to.
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display = al_create_display(SCREEN_W, SCREEN_H);
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if (!display)
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abort_example("Error creating display\n");
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timer = al_create_timer(1.0 / FPS); // Run at 30FPS
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queue = al_create_event_queue();
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al_register_event_source(queue, al_get_keyboard_event_source());
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al_register_event_source(queue, al_get_display_event_source(display));
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al_register_event_source(queue, al_get_timer_event_source(timer));
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al_start_timer(timer);
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// --- enet setup ---
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if (enet_initialize() != 0)
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abort_example("An error occurred while initializing ENet.\n");
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client = create_client();
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server = connect_client(client, port);
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// --- game loop ---
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bool direction_changed = false;
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while (!done) {
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al_wait_for_event(queue, &event); // Wait for and get an event.
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switch (event.type) {
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case ALLEGRO_EVENT_DISPLAY_CLOSE:
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done = true;
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break;
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case ALLEGRO_EVENT_KEY_DOWN:
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switch (event.keyboard.keycode) {
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case ALLEGRO_KEY_W: dy -= 1; direction_changed = true; break;
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case ALLEGRO_KEY_S: dy += 1; direction_changed = true; break;
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case ALLEGRO_KEY_A: dx -= 1; direction_changed = true; break;
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case ALLEGRO_KEY_D: dx += 1; direction_changed = true; break;
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}
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break;
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case ALLEGRO_EVENT_KEY_UP:
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switch (event.keyboard.keycode) {
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case ALLEGRO_KEY_W: dy += 1; direction_changed = true; break;
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case ALLEGRO_KEY_S: dy -= 1; direction_changed = true; break;
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case ALLEGRO_KEY_A: dx += 1; direction_changed = true; break;
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case ALLEGRO_KEY_D: dx -= 1; direction_changed = true; break;
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}
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break;
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case (ALLEGRO_EVENT_TIMER):
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update = true;
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break;
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}
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// update, but only if the event queue is empty
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if (update && al_is_event_queue_empty(queue)) {
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update = false;
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// if player changed direction this frame, notify the server.
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// only check once per frame to stop clients from flooding the server
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if (direction_changed) {
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direction_changed = false;
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ClientMessage msg = { dx, dy };
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ENetPacket *packet = enet_packet_create(&msg,
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sizeof(msg),
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ENET_PACKET_FLAG_RELIABLE);
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enet_peer_send(server, 0, packet);
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}
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// this will send our queued direction message if we have one, and get
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// position updates for other clients
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send_receive(client);
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// draw each player
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al_clear_to_color(al_map_rgb_f(0, 0, 0));
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for (int i = 0; i < MAX_PLAYER_COUNT; i++) {
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if (!players[i].active) continue;
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int x = players[i].x;
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int y = players[i].y;
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ALLEGRO_COLOR color = players[i].color;
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al_draw_filled_circle(x, y, PLAYER_SIZE, color);
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}
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al_flip_display();
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}
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}
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disconnect_client(client, server);
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enet_host_destroy(client);
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enet_deinitialize();
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}
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/* vim: set sts=3 sw=3 et: */

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