04: add boilerplate code for a collision scene

04-collision/client/Makefile

@@ -0,0 +1,28 @@
+CC=gcc 
+CFLAGS=`pkg-config --cflags sdl2 SDL2_image SDL2_net`
+LDFLAGS=`pkg-config --libs sdl2 SDL2_image SDL2_net`
+TARGET=client
+SDIR=src
+ADIR=assets
+ODIR=build
+
+SRC=$(shell find $(SDIR) -type f -name *.c) 
+OBJ=$(SRC:.c=.o)
+
+all: $(TARGET)
+
+.PHONY: default
+$(TARGET): $(OBJ) 
+	mkdir -p build 
+	cp -rf $(ADIR) $(ODIR)/$(ADIR)
+	$(CC) -o $(ODIR)/$@ $^ $(LDFLAGS)
+
+%.o: %.c 
+	$(CC) $(CFLAGS) -o $@ -c $< 
+
+run: 
+	$(ODIR)/$(TARGET)
+
+.PHONY: clean 
+clean: 
+	rm -f $(ODIR)/$(TARGET) $(OBJ)

04-collision/client/README.md

@@ -0,0 +1,3 @@
+# Collision - Client
+
+Client-side code for 04-collision

04-collision/client/src/defs.h

@@ -0,0 +1,37 @@
+#ifndef DEFS_H
+#define DEFS_H
+
+#include <SDL2/SDL.h>
+
+// Server details
+#define SERVER_ADDR "127.0.0.1"
+#define SERVER_PORT 9080
+
+// ERRORS 
+#define STDOK 0
+#define STDERR -1 
+#define MEMERR -2
+
+// SDL2 
+#define SCREEN_WIDTH 1000
+#define SCREEN_HEIGHT 480
+#define WINDOW_FLAGS SDL_WINDOW_SHOWN | SDL_WINDOW_OPENGL
+#define RENDERER_FLAGS SDL_RENDERER_ACCELERATED
+
+// MCS: Message Communication Standard
+#define SERVER_MESSAGE_LEN 10
+#define CLIENT_MESSAGE_LEN 7
+
+// MFS: Message Format Standard
+#define PLAYER_CONNECT_FORMAT 0
+#define OBJECT_PROPERTIES_FORMAT 1
+#define PLAYER_DISCONNECT_FORMAT 2
+
+// MSCA: Message Communication Standard Actions
+#define LEFT_MOVEMENT   0b10000000
+#define RIGHT_MOVEMENT  0b01000000
+#define UP_MOVEMENT     0b00100000
+#define DOWN_MOVEMENT   0b00010000
+#define NO_MOVEMENT     0b00000000
+
+#endif 

04-collision/client/src/format.c

@@ -0,0 +1,62 @@
+#include <SDL2/SDL.h>
+#include "defs.h"
+#include "structs.h"
+#include "format.h"
+
+extern SDL_Texture *idle_down_animation;
+extern struct object *create_object(SDL_Texture *texture, int scale, int resolution);
+
+int handle_player_connect(int *message, struct object ***map, int *slots) {
+    int object_id = message[1]; 
+    
+    if (object_id >= *slots) {
+        *slots = object_id+1;
+        *map = realloc(*map, sizeof(struct object *)*(*slots));
+    }
+
+    if (*map == NULL) 
+        return MEMERR; 
+
+    struct object *new_object = create_object(idle_down_animation, 4, 64);
+    if (new_object == NULL) 
+        return MEMERR; 
+
+    new_object->id = object_id;
+    new_object->x = message[2]; 
+    new_object->y = message[3]; 
+    new_object->colliding = message[4]; 
+    new_object->force = message[5]; 
+    new_object->state = message[6];
+    (*map)[object_id] = new_object;
+
+    return STDOK;
+}
+
+int handle_object_properties(int *message, struct object ***map, int *slots) {
+    int object_id = message[1]; 
+
+    if (object_id >= *slots) {
+        *slots = object_id+1;
+        *map = realloc(*map, sizeof(struct object *)*(*slots));
+    }
+
+    if (*map == NULL)
+        return MEMERR;
+    
+    if ((*map)[object_id] == NULL) {
+        struct object *new_object = create_object(idle_down_animation, 4, 64);
+        if (new_object == NULL) 
+            return MEMERR;
+
+        new_object->id = object_id;
+        (*map)[object_id] = new_object;
+    }
+
+    (*map)[object_id]->x = message[2];
+    (*map)[object_id]->y = message[3];
+    (*map)[object_id]->colliding = message[4];
+    (*map)[object_id]->force = message[5];
+    (*map)[object_id]->state = message[6];
+
+    return STDOK;
+}

04-collision/client/src/format.h

@@ -0,0 +1,9 @@
+#ifndef FORMAT_H
+#define FORMAT_H
+
+#include <stdlib.h>
+
+int handle_player_connect(int *message, struct object ***map, int *slots);
+int handle_object_properties(int *message, struct object ***map, int *slots);
+
+#endif

04-collision/client/src/main.c

@@ -0,0 +1,278 @@
+#include <stdio.h>
+#include <SDL2/SDL.h>
+#include <SDL2/SDL_image.h>
+#include <SDL2/SDL_net.h>
+#include "structs.h"
+#include "defs.h"
+#include "format.h"
+
+#define DEBUG 1
+
+int game_running = 1;
+struct game game; 
+int movement_speed = 10;
+double delta_time; 
+double last_frame;
+
+// network
+TCPsocket server_socket;
+
+// textures
+SDL_Texture *idle_animation;
+SDL_Texture *move_left_animation;
+SDL_Texture *move_right_animation;
+SDL_Texture *move_up_animation;
+SDL_Texture *move_down_animation;
+SDL_Texture *idle_left_animation;
+SDL_Texture *idle_right_animation;
+SDL_Texture *idle_up_animation;
+SDL_Texture *idle_down_animation;
+
+// scene
+int objects_count = 0;
+struct object ** objects_map;
+
+void prepare_scene(void) {
+    SDL_SetRenderDrawColor(game.renderer, 96, 128, 255, 255);
+    SDL_RenderClear(game.renderer);
+}
+
+void key(SDL_KeyboardEvent *event) {
+    if (event->repeat != 0)
+        return;   
+
+    if (event->keysym.scancode == SDL_SCANCODE_D)
+        game.left = !game.left;
+    if (event->keysym.scancode == SDL_SCANCODE_F)
+        game.right = !game.right;
+    if (event->keysym.scancode == SDL_SCANCODE_K)
+        game.up = !game.up;
+    if (event->keysym.scancode == SDL_SCANCODE_J)
+        game.down = !game.down;
+}
+
+void handle_input(void) {
+    SDL_Event event; 
+
+    while (SDL_PollEvent(&event)) {
+        switch (event.type) {
+            case SDL_QUIT: 
+                game_running = 0; 
+                break;
+            case SDL_KEYDOWN: 
+            case SDL_KEYUP: 
+                key(&event.key); 
+                break;
+            default:
+                break;
+        }
+        if (event.type == SDL_QUIT) 
+            game_running = 0;
+    }
+}
+
+SDL_Texture *load_texture(const char *path) {
+    SDL_Texture *texture; 
+    
+    SDL_LogMessage(SDL_LOG_CATEGORY_APPLICATION, SDL_LOG_PRIORITY_INFO, "Loading %s", path);
+    
+    texture = IMG_LoadTexture(game.renderer, path);
+
+    return texture;
+}
+
+void present_scene(void) {
+    SDL_RenderPresent(game.renderer);
+}
+
+int new_key_position(void **map, int slots) {
+    int slot = 0; 
+
+    if (slots <= 0) 
+        return slot; 
+
+    if (map == NULL) 
+        return slot; 
+
+    while (slot <= slots) {
+        if (map[slots] == NULL) 
+            break;
+
+        slot++;
+    }
+
+    return slot;
+}
+
+int handle_server(void *data) {
+    for (;;) {
+        int message[CLIENT_MESSAGE_LEN];
+        int recv_len = SDLNet_TCP_Recv(server_socket, message, sizeof(int)*CLIENT_MESSAGE_LEN);
+
+        if (!recv_len) {
+            fprintf(stderr, "Error: failed receiving message from server\n%s\n", SDLNet_GetError());
+            break;
+        }
+
+        if (DEBUG) 
+            fprintf(stdout, "Notice: received '%d' bytes from server\n", recv_len);
+
+        if (message[0] == PLAYER_CONNECT_FORMAT) {
+            if (DEBUG) 
+                fprintf(stdout, "DEBUG: PLAYER CONNECT MESSAGE\n");
+
+            int ret = handle_player_connect(message, &objects_map, &objects_count);
+            if (ret == MEMERR) {
+                fprintf(stderr, "MEMERR: Failed handling memory for player connect\n");
+                return MEMERR;
+            }
+
+            continue; 
+        }
+
+        if (message[0] == OBJECT_PROPERTIES_FORMAT) {
+            if (DEBUG) 
+                fprintf(stdout, "DEBUG: OBJECT PROPERTIES MESSAGE FOR ID %d\n", message[1]);
+            
+            int ret = handle_object_properties(message, &objects_map, &objects_count);
+            if (ret == MEMERR) {
+                fprintf(stderr, "MEMERR: Failed handling memory for new object properties\n");
+                return MEMERR;
+            }
+
+            continue; 
+        }
+
+        if (message[0] == PLAYER_DISCONNECT_FORMAT) {
+            if (DEBUG) 
+                fprintf(stdout, "DEBUG: PLAYER DISCONNECT MESSAGE\n");
+
+            int object_id = message[1]; 
+
+            free(objects_map[object_id]);
+            objects_map[object_id] = NULL; 
+
+            continue;
+        }
+    }
+
+    return 0; 
+}
+
+int connect_to_server(void) {
+    IPaddress ip; 
+    if (SDLNet_ResolveHost(&ip, SERVER_ADDR, SERVER_PORT) != 0) {
+        fprintf(stderr, "Error: resolving host of server\n%s\n", SDLNet_GetError());
+        return -1;
+    }
+
+    server_socket = SDLNet_TCP_Open(&ip);
+    if (!server_socket) {
+        fprintf(stderr, "Error: failed opening socket to '%s' at '%d'\n%s\n", SERVER_ADDR, SERVER_PORT, SDLNet_GetError());
+        return -1;
+    }
+
+    SDL_CreateThread(handle_server, "server", NULL);
+
+    return 0;
+}
+
+int main(int argc, char *argv[]) {
+    if (SDL_Init(SDL_INIT_VIDEO) != 0) {
+        fprintf(stderr, "Error: could not initialize SDL\n%s\n", SDL_GetError());
+        return -1;
+    }
+
+    if (SDLNet_Init() != 0) {
+        fprintf(stderr, "Error: could not initialize SDL net\n%s\n", SDL_GetError());
+        return -1;
+    }
+
+    game.window = SDL_CreateWindow("03-network", SDL_WINDOWPOS_UNDEFINED, SDL_WINDOWPOS_UNDEFINED, SCREEN_WIDTH, SCREEN_HEIGHT, WINDOW_FLAGS);
+
+    if (game.window == NULL) {
+        fprintf(stderr, "Error: could not create window\n%s\n", SDL_GetError());
+        return -1;
+    }
+
+    game.renderer = SDL_CreateRenderer(game.window, -1, RENDERER_FLAGS);
+
+    if (game.renderer == NULL) {
+        fprintf(stderr, "Error: could not create renderer\n%s\n", SDL_GetError());
+        return -1;
+    }
+
+    // load player animations 
+    move_left_animation = load_texture("assets/player/move_left.png");
+    move_right_animation = load_texture("assets/player/move_right.png");
+    move_up_animation = load_texture("assets/player/move_up.png");
+    move_down_animation = load_texture("assets/player/move_down.png");
+    idle_left_animation = load_texture("assets/player/idle_left.png");
+    idle_right_animation = load_texture("assets/player/idle_right.png");
+    idle_up_animation = load_texture("assets/player/idle_up.png");
+    idle_down_animation = load_texture("assets/player/idle_down.png");
+    idle_animation = idle_down_animation;
+
+    if (connect_to_server() != 0)
+        return -1;
+
+    // game loop
+    while (game_running) {
+        double current_frame = SDL_GetTicks();
+        delta_time = current_frame - last_frame;
+        last_frame = current_frame;
+
+        prepare_scene();
+        handle_input(); 
+
+        uint8_t message[SERVER_MESSAGE_LEN];
+        message[0] = (game.left << 7)  | 
+                     (game.right << 6) |
+                     (game.up << 5)    | 
+                     (game.down << 4);
+
+        SDLNet_TCP_Send(server_socket, message, sizeof(uint8_t)*SERVER_MESSAGE_LEN);
+
+        for (int iter = 0; iter < objects_count; iter++) {
+            struct object *obj = objects_map[iter];
+            if (obj == NULL) 
+                continue; 
+
+            if (obj->state & LEFT_MOVEMENT) {
+                switch_animation(obj, move_left_animation); 
+                idle_animation = idle_left_animation;
+            }
+
+            if (obj->state & RIGHT_MOVEMENT) {
+                switch_animation(obj, move_right_animation); 
+                idle_animation = idle_right_animation;
+            }
+
+            if (obj->state & UP_MOVEMENT) {
+                switch_animation(obj, move_up_animation);
+                idle_animation = idle_up_animation;
+            }
+
+            if (obj->state & DOWN_MOVEMENT) {
+                switch_animation(obj, move_down_animation);
+                idle_animation = idle_down_animation;
+            }
+
+            if (obj->state == NO_MOVEMENT) 
+                switch_animation(obj, idle_animation);
+
+            obj->animation_speed = 6;
+
+            draw_object(&game, obj);
+        }
+
+        present_scene();
+
+        SDL_Delay(16);
+    }
+
+    SDL_DestroyWindow(game.window);
+    SDL_Quit();
+
+    return 0; 
+}

04-collision/client/src/object.c

@@ -0,0 +1,54 @@
+#include "structs.h"
+
+extern double delta_time;
+
+struct object *create_object(SDL_Texture *texture, int scale, int resolution) {
+    struct object *object = (struct object *) calloc(1, sizeof(struct object));
+
+    if (object == NULL) 
+        return NULL;
+
+    object->texture = texture;
+    object->resolution = resolution;
+    object->animation_speed = 13;
+    object->scale = scale;
+
+    return object;
+}
+
+void draw_object(struct game *game, struct object *object) {
+    int texture_width; 
+    SDL_Rect src;
+    SDL_Rect dest;
+
+    src.x = object->animation_slide * object->resolution;
+    src.y = 0;
+
+    src.w = object->resolution;
+    src.h = object->resolution;
+
+    dest.x = object->x; 
+    dest.y = object->y; 
+    dest.w = object->resolution * object->scale;
+    dest.h = object->resolution * object->scale;
+
+    SDL_RenderCopyEx(game->renderer, object->texture, &src, &dest, 0, NULL, object->flip);
+
+    // update animation slide
+    SDL_QueryTexture(object->texture, NULL, NULL, &texture_width, NULL);
+
+    object->animation_clock += object->animation_speed*(delta_time/1000);
+
+    if (object->animation_clock >= 1) {
+        object->animation_clock = 0;    
+        object->animation_slide = (object->animation_slide+1) % (texture_width / object->resolution); // clock arithmetic: jump back to first animation slide 
+    }
+}
+
+void switch_animation(struct object *object, SDL_Texture *animation) {
+    if (object->texture == animation)
+        return;
+
+    object->animation_slide = 0; 
+    object->texture = animation;
+}

04-collision/client/src/structs.h

@@ -0,0 +1,48 @@
+#ifndef STRUCTS_H
+#define STRUCTS_H
+
+#include <SDL2/SDL.h>
+
+struct game {
+    SDL_Window *window; 
+    SDL_Renderer *renderer;
+
+    int left; 
+    int right;
+    int up; 
+    int down;
+};
+
+struct animation {
+    SDL_Texture *tilemap;   
+    int resolution;
+
+    int skippable;
+};
+
+struct object {
+    SDL_Texture *texture;
+    int resolution;                 // of the texture/every tile
+    int id;
+
+    int x; 
+    int y;
+    int scale;
+    Uint32 flip;
+
+    // animation 
+    double animation_clock;         // everytime it reaches 1, the texture switches to the next slide
+    double animation_speed;         // how fast will the clock reach 1 with respect to delta_time
+    int animation_slide;            // the current slide of the animation
+    
+    uint8_t state;
+
+    int colliding;
+    int force;
+};
+
+struct object *create_object(SDL_Texture *texture, int scale, int resolution);
+void draw_object(struct game *game, struct object *object);
+void switch_animation(struct object *object, SDL_Texture *animation); 
+
+#endif 

04-collision/server/Makefile

@@ -0,0 +1,28 @@
+CC=gcc 
+CFLAGS=`pkg-config --cflags sdl2 SDL2_net`
+LDFLAGS=`pkg-config --libs sdl2 SDL2_net`
+TARGET=server
+SDIR=src
+ADIR=assets
+ODIR=build
+
+SRC=$(shell find $(SDIR) -type f -name *.c) 
+OBJ=$(SRC:.c=.o)
+
+all: $(TARGET)
+
+.PHONY: default
+$(TARGET): $(OBJ) 
+	mkdir -p build 
+	cp -rf $(ADIR) $(ODIR)/$(ADIR)
+	$(CC) -o $(ODIR)/$@ $^ $(LDFLAGS)
+
+%.o: %.c 
+	$(CC) $(CFLAGS) -o $@ -c $< 
+
+run: 
+	$(ODIR)/$(TARGET)
+
+.PHONY: clean 
+clean: 
+	rm -f $(ODIR)/$(TARGET) $(OBJ)

04-collision/server/README.md

@@ -0,0 +1,3 @@
+# Collision - Server
+
+Server-side code for 04-collision

04-collision/server/src/defs.h

@@ -0,0 +1,31 @@
+#ifndef DEFS_H
+#define DEFS_H
+
+// DEBUG 
+#define GENERAL_DEBUG   0x0001
+#define PLAYER_DEBUG    0x0010
+
+// ERRORS 
+#define STDERR -1
+#define MEMERR -2
+
+// MCS: Message Communication Standard
+#define SERVER_MESSAGE_LEN 10
+#define CLIENT_MESSAGE_LEN 7
+
+// MFS: Message Format Standard
+#define PLAYER_CONNECT_FORMAT 0
+#define OBJECT_PROPERTIES_FORMAT 1
+#define PLAYER_DISCONNECT_FORMAT 2
+
+// MCSA: Message Communication Standard Actions
+#define LEFT_MOVEMENT   0b10000000
+#define RIGHT_MOVEMENT  0b01000000
+#define UP_MOVEMENT     0b00100000
+#define DOWN_MOVEMENT   0b00010000
+
+// OC: Object Constants
+#define GRAVITY 2
+#define MOVEMENT_SPEED 10
+
+#endif 

04-collision/server/src/main.c

@@ -0,0 +1,216 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <signal.h>
+#include <SDL2/SDL.h>
+#include <SDL2/SDL_net.h>
+#include <SDL2/SDL_error.h>
+#include "defs.h"
+#include "structs.h"
+#include "structures.h"
+
+#define DEBUG 0x0010
+#define PORT 9080
+
+struct object **objects_map;
+int objects_map_size = 0;
+int objects_count = 0;
+
+struct connection **connections_map;
+int connections_map_size = 0; 
+int connections_count = 0; 
+
+void handle_player_input(struct object *obj, char *message) {
+    uint8_t action = message[0];
+
+    if (action & LEFT_MOVEMENT)
+        obj->x -= MOVEMENT_SPEED; 
+
+    if (action & RIGHT_MOVEMENT) 
+        obj->x += MOVEMENT_SPEED;
+
+    if (action & UP_MOVEMENT) 
+        obj->y -= MOVEMENT_SPEED; 
+
+    if (action & DOWN_MOVEMENT) 
+        obj->y += MOVEMENT_SPEED; 
+
+    obj->state = action;
+}
+
+void handle_player_physics(struct object *obj) {
+}
+
+int broadcast_event(int format, int object_id) {
+    struct object *obj = objects_map[object_id];
+
+    for (int iter = 0; iter < connections_map_size; iter++) {
+        struct connection *con = connections_map[iter]; 
+        if (con == NULL) 
+            continue; 
+
+        int message[] = {
+            format, 
+            obj->id, 
+            obj->x, 
+            obj->y, 
+            obj->colliding, 
+            obj->force,
+            obj->state
+        };
+
+        SDLNet_TCP_Send(con->socket, message, sizeof(int)*CLIENT_MESSAGE_LEN);
+    }
+
+    return 0;
+}
+
+int handle_player(void *data) {
+    struct connection *connection_data = (struct connection *) data;
+    struct object *obj = objects_map[connection_data->obj_id];
+
+    SDLNet_SocketSet set = SDLNet_AllocSocketSet(1);
+    if (set == NULL) {
+        fprintf(stderr, "Error: cannot allocate memory for a new socket set\n");
+        return -1;
+    }
+
+    int ret = SDLNet_TCP_AddSocket(set, connection_data->socket);
+    if (ret == -1) {
+        fprintf(stderr, "Error: max socket count in socket set reached\n");
+        return -1;
+    }
+
+    broadcast_event(PLAYER_CONNECT_FORMAT, connection_data->obj_id);
+
+    for (;;) {
+        char message[SERVER_MESSAGE_LEN]; 
+        int ready_sockets = SDLNet_CheckSockets(set, 100); 
+        if (ready_sockets == -1) {
+            fprintf(stderr, "Error: cannot call select() system call with SDLNet_CheckSockets()\n");
+            continue;
+        } 
+        
+        if (ready_sockets == 0)
+            goto update_client;
+
+        int recv_len = SDLNet_TCP_Recv(connection_data->socket, message, SERVER_MESSAGE_LEN);
+        if (!recv_len) { 
+            // player disconnected
+            fprintf(stderr, "Error: failed receiving message\n%s\n", SDLNet_GetError());
+            break;
+        }
+
+        if (DEBUG & GENERAL_DEBUG) 
+            fprintf(stdout, "Notice: received '%s' and '%d' bytes\n", message, recv_len);
+    
+        handle_player_input(obj, message);
+
+    update_client:
+        handle_player_physics(obj);
+        broadcast_event(OBJECT_PROPERTIES_FORMAT, connection_data->obj_id);
+    }
+
+    // Communicate client disconnect
+    broadcast_event(PLAYER_DISCONNECT_FORMAT, connection_data->obj_id);
+
+    SDLNet_FreeSocketSet(set);
+    SDLNet_TCP_Close(connection_data->socket);
+
+    objects_map[connection_data->obj_id] = NULL;
+    objects_count--;
+
+    connections_map[connection_data->id] = NULL;
+    connections_count--;
+
+    free(obj);
+    free(data);
+
+    return 0;
+}
+
+void catch_alarm(int sig) {
+    fprintf(stdout, "Notice: force stopping server...\n");
+    exit(EXIT_SUCCESS);
+}
+
+int new_key_position(void **map, int slots) {
+    int slot = 0; 
+
+    if (slots <= 0) 
+        return slot;
+
+    if (map == NULL) 
+        return slot;
+
+    while (slot <= slots) {
+        if (map[slot] == NULL)
+            break;
+        
+        slot++;
+    }
+
+    return slot;
+}
+
+int main(int argc, char *argv[]) {
+    signal(SIGINT, catch_alarm);
+
+    if (SDL_Init(SDL_INIT_VIDEO) != 0) {
+        fprintf(stderr, "Error: could not initialize SDL\n%s\n", SDL_GetError());
+        return -1;
+    }
+
+    if (SDLNet_Init() != 0) {
+        fprintf(stderr, "Error: could not initialize SDL net\n%s\n", SDL_GetError());
+        return -1;
+    }
+
+    IPaddress ip; 
+    if (SDLNet_ResolveHost(&ip, NULL, PORT) == -1) {
+        fprintf(stderr, "Error: failed resolving host \n%s\n", SDL_GetError());
+        return -1;
+    }
+
+    TCPsocket server = SDLNet_TCP_Open(&ip); 
+    if (!server) {
+        fprintf(stderr, "Error: failed opening socket at %d\n%s\n", PORT, SDL_GetError());
+        return -1;
+    }
+
+    for (;;) {
+        TCPsocket client = SDLNet_TCP_Accept(server);
+        if (!client) {
+            SDL_Delay(100); 
+            continue;
+        }
+
+        fprintf(stdout, "Notice: accepted a connection from client!\n"); 
+
+        int new_object_slot = map_allocate_value((void ***) &objects_map, &objects_map_size, &objects_count, sizeof(struct object));
+        if (new_object_slot == MEMERR) {
+            fprintf(stderr, "MEMERR: failed allocating memory for new object\n");
+            return STDERR;
+        }
+
+        int new_connection_slot = map_allocate_value((void ***) &connections_map, &connections_map_size, &connections_count, sizeof(struct connection));
+        if (new_connection_slot == MEMERR) {
+            fprintf(stderr, "MEMERR: failed allocating memory for new connection\n");
+            return STDERR;
+        }
+
+        struct object *new_object = objects_map[new_object_slot];
+        struct connection *new_connection = connections_map[new_connection_slot];
+
+        new_object->id = new_object_slot;
+        new_connection->id = new_connection_slot;
+        new_connection->socket = client;
+        new_connection->obj_id = new_object_slot;
+
+        if (DEBUG & PLAYER_DEBUG) 
+            fprintf(stdout, "Created connection with id '%d' and object '%d'\n", new_connection->id, new_object->id);
+
+        SDL_CreateThread(handle_player, "client", new_connection);
+    }
+
+    return 0;
+}

04-collision/server/src/structs.h

@@ -0,0 +1,23 @@
+#ifndef STRUCTS_H
+#define STRUCTS_H
+
+#include <SDL2/SDL_net.h>
+
+struct connection {
+    int id;
+    int obj_id;
+    TCPsocket socket;
+};
+
+struct object {
+    int id;
+    int x;
+    int y;
+
+    int colliding;
+    int force;
+    
+    uint8_t state;
+};
+
+#endif

04-collision/server/src/structures.c

@@ -0,0 +1,55 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include "structures.h"
+#include "defs.h"
+
+int map_find_empty_slot(void **map, int slots) {
+    int slot = 0; 
+
+    if (slots <= 0) 
+        return slot;
+
+    if (map == NULL) 
+        return slot;
+
+    while (slot < slots) {
+        if (map[slot] == NULL)
+            break;
+        
+        slot++;
+    }
+
+    return slot;
+}
+
+// If there's Nx fewer used slots than total slots in the map, find the first possible one.
+// Else reallocate the map and use the end slot 
+// Then allocate an object of size BYTES and add it into the map.
+int map_allocate_value(void ***map, int *total_slots, int *used_slots, int bytes) {
+    int half_slots = (*total_slots) / 2;
+    int empty_slot = 0; 
+    
+    if (*used_slots < half_slots) {
+        empty_slot = map_find_empty_slot(*map, *used_slots); 
+        goto jump;   
+    } 
+
+    empty_slot = *total_slots;
+    (*total_slots)++;
+    *map = realloc(*map, sizeof(void *)*(*total_slots));
+
+jump: 
+    if (*map == NULL) 
+        return MEMERR; 
+
+    void *new_value = calloc(1, bytes); 
+    if (new_value == NULL) 
+        return MEMERR; 
+
+    (*used_slots)++;
+    (*map)[empty_slot] = new_value;
+
+    return empty_slot;
+}
+
+

04-collision/server/src/structures.h

@@ -0,0 +1,9 @@
+#ifndef STRUCTURES_H
+#define STRUCTURES_H 
+
+#include "structs.h"
+
+int map_find_empty_slot(void **map, int slots);
+int map_allocate_value(void ***map, int *total_slots, int *used_slots, int bytes);
+
+#endif