diff --git a/src/game.c b/src/game.c
index f424503..6488d18 100644
--- a/src/game.c
+++ b/src/game.c
@@ -7,6 +7,7 @@ void game_logic(Game *game) {
 }
 
 void draw(Game *game) {
+    /* Draw everything. */
     render_map(&game->player, game->map_level);
     player_draw(&game->player);
 }
diff --git a/src/main.c b/src/main.c
index 21ff533..4f62c76 100644
--- a/src/main.c
+++ b/src/main.c
@@ -31,10 +31,18 @@ Game game = {
 };
 
 /* some global variables */
-bool exittoOS = false;        // set to true when asked for exit
 
-bool screenshot = false;    // set to true when screenshot is required
-bool record = false;        // set to true when
+/* Set to true when asked for exit */
+bool exittoOS = false;
+
+/* Set to true when screenshot is required */
+bool screenshot = false;
+
+/* Set to true when recording a video of the screen is required */
+bool record = false;
+
+/* How many ms the frame already took. */
+long int frame_duration;
 
 /* Key management */
 
@@ -162,3 +170,4 @@ int main(void) {
 
     return 1;
 }
+
diff --git a/src/map.c b/src/map.c
index c52c70a..840dcea 100644
--- a/src/map.c
+++ b/src/map.c
@@ -97,6 +97,8 @@ void render_map(Player *player, Map *map_level) {
 } */
 
 short int get_tile(Map *map_level, int x, int y, int l) {
+    /* Get the tile at (x, y) on layer l. Returns the tile ID or MAP_OUTSIDE if
+     * she's not found. */
     return x>=0 && x < map_level->w && y>=0 && y < map_level->h ?
         map_level->layers[l][y * map_level->w + x] : MAP_OUTSIDE;
 }
diff --git a/src/player.c b/src/player.c
index e5094f1..eadf11f 100644
--- a/src/player.c
+++ b/src/player.c
@@ -26,6 +26,7 @@ const char one_px_mov[8] = {
 
 /* TODO: Search for all hard tiles in the tileset. hard_tiles is a list of their
  * IDs */
+/* The tiles where the player can't go trough. */
 #define HARD_TILES_AMOUNT 5
 const short int hard_tiles[HARD_TILES_AMOUNT] = {
     MAP_OUTSIDE, 124, 148, 125, 149
@@ -41,9 +42,12 @@ void player_move(Map *map_level, Player *player, Direction direction) {
     /* How this player movement will modify the player x and y. */
     const char dx = one_px_mov[direction*2]*SPEED;
     const char dy = one_px_mov[direction*2+1]*SPEED;
+    /* If the player will collide with a hard tile. */
     if(player_collision(map_level, player, direction)){
+        /* I fix his position so he won't be partially in the tile. */
         player_fix_position(player, dx, dy);
     }else{
+        /* If he won't collide I just move him normally */
         player->x += dx;
         player->y += dy;
     }
@@ -56,20 +60,25 @@ void player_action(Player *player) {
 bool player_collision(Map *map_level, Player *player, Direction direction) {
     /* What's the tile the player is going to. */
     short int i;
+    /* Where is the tile where he will go to from his position. */
     const char dx = one_px_mov[direction*2];
     const char dy = one_px_mov[direction*2+1];
+    /* The tile he will go to. */
     int player_tile_x = player->x/T_WIDTH;
     int player_tile_y = player->y/T_HEIGHT;
     for(i=0;i<map_level->nblayers;i++){
+        /* if he's on a hard tile */
         if(is_in((short int*)hard_tiles, HARD_TILES_AMOUNT,
                  get_tile(map_level, player_tile_x+dx, player_tile_y+dy, i))){
-            return true;
+            return true; /* He will collide with it. */
         }
     }
-    return false;
+    return false; /* He won't collide with a hard tile. */
 }
 
 void player_fix_position(Player *player, bool fix_x, bool fix_y) {
+    /* I fix his poition on x or/and on y if y need to, so that he won't be over
+     * the hard tile that he collided with. */
     if(fix_x) player->x = player->x/T_WIDTH*T_WIDTH+P_WIDTH/2;
     if(fix_y) player->y = player->y/T_HEIGHT*T_HEIGHT+P_HEIGHT/2;
 }