Game Python Postgres and Save Game
Introduction
In this part, we continue building a game with Python and Postgres and Save Game as part 8 of a multi-part series of lessons where the final result is a 2D top-down-view videogame like Pac Man, where the purpose is to “eat” powerups while avoiding monsters. We chose to use the Arcade framework for Python for its game-related methods and functions. We used Postgres to read and write screen and object (player, enemies, obstacles, and power-ups) data. In this lesson we will explore using Postgres again to store and retrieve saved games. In future articles we will add player registration, player login, multi-player and a screen editor.
Prerequisites
See part 1 through 7, where we learned how to draw a screen, create tables in Postgres for storing and reading screen data and screen objects as Sprites, reading keys to control player movement, added random movements to the monsters, collision detection, intelligent player tracking for the monsters, and sound effects. Please peruse the previous sections of this lesson, starting at Build game with Python and draw a screen.
I will assume you followed the previous sections of this series, so we will leave the following out of this article: creating the Postgres tables, re-doing the details of setting up a window with Arcade, and Sprite movement mechanices, except for in the source code at the end of this part eight. So, before the final code at the bottom, we’ll build some functions for loading and saving a game’s progress to Postgres.
NOTE: tbl_games has an auto-incrementing unique indexed column we called “id”.
Save game in Python
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 | # First we use SELECT SQL to check whether # a saved screen exists for the current user. # so yes, one save per user. s = "" s += "SELECT" s += " id" s += " FROM tbl_games" s += " WHERE id_user = " + id_user db_cursor.execute(s) db_row = db_cursor.fetchone() # Check to see if a row was returned # If not then we set i_rows to zero if db_row == None: i_rows = 0 else: # In this case, a row was returned. # Get data from that row i_rows = 1 id = db_row[0] if i_rows == 0: # If no rows were returned, this means # we want to add a new record via the INSERT INTO # SQL command. s = "" s += "INSERT INTO tbl_games (" s += " id_screen" s += ", id_user" s += ", i_hit_points" s += ", i_points" s += ", i_lives" s += ") VALUES (" s += id_screen s += "," + id_user s += "," + i_hit_points s += "," + i_points s += "," + i_lives s += ")" db_cursor.execute(s) else: # If a row was returned, we use the id column # of that returned row in our WHERE clause # so we overwrite that record in the database. s = "" s += "UPDATE tbl_games SET" s += " id_screen = " + id_screen s += ", i_hit_points = " + i_hit_points s += ", i_points = " + i_points s += ", i_lives = " + i_lives s += " WHERE id = " + id db_cursor.execute(s) |
Load game in Python
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 | s = "" s += "SELECT TOP 1" s += " id_screen = " + id_screen s += ", i_hit_points = " + i_hit_points s += ", i_points = " + i_points s += ", i_lives = " + i_lives s += " FROM tbl_games" s += " WHERE id_user = " + id_user try: db_cursor.execute(s) db_row = db_cursor.fetchone() # Pull data from id_screen = db_row[0] i_hit_points = db_row[1] i_points = db_row[2] i_lives = db_row[3] except psycopg2.Error as e: t_msg = "SQL error: " + e + "/n SQL: " + s return render_template("error.html", t_msg = t_msg) |
Now that we have looked at our two new features, load game and save game, we can dive into the commented full source game code:
Full source code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 | import arcade import psycopg2 import random from flask import Flask from flask import render_template # connect to database t_host = "PostgreSQL database host address" t_port = "5432" t_dbname = "database name" t_user = "database user name" t_pw = "password" db_conn = psycopg2.connect(host=t_host, port=t_port, dbname=t_dbname, user=t_user, password=t_pw) db_cursor = db_conn.cursor() # Initialize global vars # In a future lesson we will add registration and sign in # For now, there is only one user ID; zero. id_user = 0 id_screen = 0 t_title = "" t_color = "" i_width = 0 i_height = 0 i_enemy_hit = 0 i_hit_points = 100 i_points = 0 i_lives = 3 # initialize as list: t_hit_sound = [] @app.route("/main") def gameLoad(): s = "" s += "SELECT TOP 1" s += " id_screen = " + id_screen s += ", i_hit_points = " + i_hit_points s += ", i_points = " + i_points s += ", i_lives = " + i_lives s += " FROM tbl_games" s += " WHERE id_user = " + id_user try: db_cursor.execute(s) db_row = db_cursor.fetchone() id_screen = db_row[0] i_hit_points = db_row[1] i_points = db_row[2] i_lives = db_row[3] except psycopg2.Error as e: t_msg = "SQL error: " + e + "/n SQL: " + s return render_template("error.html", t_msg = t_msg) db_cursor.close def gameSave(): # first see if a save exists for this user s = "" s += "SELECT" s += " id" s += " FROM tbl_games" s += " WHERE id_user = " + id_user try: db_cursor.execute(s) db_row = db_cursor.fetchone() if db_row == None: i_rows = 0 else: i_rows = 1 id = db_row[0] except psycopg2.Error as e: t_msg = "SQL error: " + e + "/n SQL: " + s return render_template("error.html", t_msg = t_msg) if i_rows == 0: s = "" s += "INSERT INTO tbl_games (" s += " id_screen" s += ", id_user" s += ", i_hit_points" s += ", i_points" s += ", i_lives" s += ") VALUES (" s += id_screen s += "," + id_user s += "," + i_hit_points s += "," + i_points s += "," + i_lives s += ")" try: db_cursor.execute(s) except psycopg2.Error as e: t_msg = "SQL error: " + e + "/n SQL: " + s return render_template("error.html", t_msg = t_msg) else: s = "" s += "UPDATE tbl_games SET" s += " id_screen = " + id_screen s += ", i_hit_points = " + i_hit_points s += ", i_points = " + i_points s += ", i_lives = " + i_lives s += " WHERE id_user = " + id_user try: db_cursor.execute(s) except psycopg2.Error as e: t_msg = "SQL error: " + e + "/n SQL: " + s return render_template("error.html", t_msg = t_msg) db_cursor.close def getScreenFromDB(): # Get columns for first row/ s = "" s += "SELECT" s += " id" s += ", t_color" s += ", t_title" s += ", i_height" s += ", i_width" s += " FROM tbl_screens" s += " WHERE id = " + id_screen try: db_cursor.execute(s) db_row = db_cursor.fetchone() id_screen = db_row[0] t_color_screen = db_row[1] t_title = db_row[2] i_height = db_row[3] i_width = db_row[4] except psycopg2.Error as e: t_msg = "SQL error: " + e + "/n SQL: " + s return render_template("error.html", t_msg = t_msg) db_cursor.close def getObjectsFromDB(): # Get objects data from tbl_screens_objects in Postgres s = "" s += "SELECT" s += " id" s += ", t_obj_name" s += ", t_obj_type" s += ", t_obj_img_URL" s += ", i_y" s += ", i_x" s += ", t_color_hit" s += ", t_properties" s += ", t_hit_sound" s += ", t_hit_action" s += ", b_hit_possible" s += ", b_hit_destroys_it" s += ", b_hit_awards" s += ", n_hit_awards" s += ", n_hit_damage" s += " FROM tbl_screens_objects" s += " WHERE (" s += " id_screen = " + id_screen s += ")" s += " ORDER BY i_order" try: db_cursor.execute(s) return db_cursor except psycopg2.Error as e: t_msg = "SQL error: " + e + "/n SQL: " + s return render_template("error.html", t_msg = t_msg) class gameWindow(arcade.Window): def__init__(self, i_width, i_height, t_title, db_cursor): super().__init__(width, height, title, resizable=false) self.set_location(100, 100) # Give our window a background color. arcade.set_background_color(arcade.color.t_color_screen) self.player_x = 100 self.player_y = 200 self.player_speed = 250 self.right = false self.left = false self.up = false self.down = false # Initialize a spritelist to track objects like walls. # This type of object only stops player motion. self.ListSpriteObjects = arcade.SpriteList() # Initialize a spritelist to track monsters/enemies. # These objects cause damage to i_hit_points. self.ListSpriteEnemies = arcade.SpriteList() # Initialize a spritelist to track powerups. # These objects give points to the player when a collision occurs. self.ListSpritePowerUps = arcade.SpriteList() # Get data from the database into the 3 lists above. i = 0 for each db_row in db_cursor: id_screen = db_row[0] t_obj_name.append(db_row[1]) t_obj_type.append(db_row[2]) t_obj_img_URL = db_row[3] i_y = db_row[4] i_x = db_row[5] t_color_hit.append(db_row[6]) t_properties.append(db_row[7]) t_hit_sound.append(arcade.load_sound(db_row[8])) t_hit_action.append(db_row[9]) b_hit_possible.append(db_row[10]) b_hit_destroys_it.append(db_row[11]) b_hit_awards.append(db_row[12]) n_hit_awards.append(db_row[13]) n_hit_damage.append(db_row[14]) # draw the current sprite in db_row if t_object_type == "obstacle": self.SpriteObject = arcade.Sprite(t_object_image_URL, i_x, i_y) # add current obstacle to growing list of Sprites (SpriteList) self.ListSpriteObjects.append(self.SpriteObject) elif t_object_type == "enemy": self.SpriteObstacle = arcade.Sprite(t_object_image_URL, i_x, i_y) # add current enemy (sprite) to growing list of Sprites (SpriteList) self.SpriteEnemies.append(self.SpriteObject) elif t_object_type == "powerup": self.SpriteObstacle = arcade.Sprite(t_object_image_URL, i_x, i_y) # add current PowerUp to growing list of Sprites (SpriteList) self.SpritePowerUps.append(self.SpriteObject) elif t_object_type == "Player": self.SpritePlayer = arcade.Sprite(t_object_image_URL, i_x, i_y) # increment the counter i += 1 def enemyMovement(): # Iterate through enemy sprites. # In this case, there are only 2 enemies but we designed this so # you can add as many as you want to add to the database. # THEN we give them a random direction out of eight # possible directions. # FINALLY we add our new-for-this-part "intelligent" direction to # the random one. for currentSprite in self.ListSpriteEnemies: x = currentSprite.position[0] y = currentSprite.position[1] # Random movement direction = random.randint(1, 8) if direction == 1: y += 2 if direction == 2: x += 2 y += 2 if direction == 3: x += 2 if direction == 4: x += 2 y -= 2 if direction == 5: y -= 2 if direction == 6: y -= 2 x -= 2 if direction == 7: x -= 2 if direction == 8: x -= 2 y += 2 # NEW "intelligent" movement. if player_y > y: y += 2 if player_x > x: x += 2 if player_y < y: y -= 2 if player_x < x: x -= 2 # Set the current monster's location on screen. currentSprite.set_position(x, y) def on_draw(self): self.SpritePlayer.draw() self.ListSpriteObjects.draw() self.ListSpriteEnemies.draw() self.ListSpritePowerUps.draw() def on_update(self, delta_time): # Delta_time is last time the # same function was used; We use this # to scale movement speed with speed of processing. if self.right = true: self.player_x += self.player_speed * delta_time if self.left = true: self.player_x -= self.player_speed * delta_time if self.up = true: self.player_y += self.player_speed * delta_time if self.down = true: self.player_y -= self.player_speed * delta_time # Set a new location based on the player's x and y coordinates: self.SpritePlayer.set_position(self.player_x, self.player_y) # Move all enemy Sprites. enemyMovement() # Update Sprite Lists: self.ListSpriteObjects.update() self.ListSpriteEnemies.update() self.ListSpritePowerUps.update() # Did the user hit a monster? i = 0 for SpriteEnemy in self.ListSpriteEnemies: b_collision = arcade.check_for_collision(SpriteEnemy, self.SpritePlayer) if b_collision == true: i_enemy_hit = i i_hit_points -= n_hit_damage[i_enemy_hit] # Graphical changes (like explosion or something) code # to show crash will go here in later lesson. # NEW: arcade.play_sound(t_hit_sound[i]) if i_hit_points < 1: i_lives -= 1 if i_lives < 1: # Dead - Next part we will build code to handle this. # For now, the player lives forever. i_hit_points = 100 i +=1 # Did the user run into a power-up? i = 0 for SpritePowerUp in self.ListSpritePowerUps: b_collision = arcade.check_for_collision(SpritePowerUp, self.SpritePlayer) if b_collision == true: i_pu_hit = i i_points += n_hit_awards[i_pu_hit] # Graphics and code to show # powerup hit will go here. # NEW: arcade.play_sound(t_hit_sound[i]) i +=1 # Did the user collide with another type of obstacle? i = 0 for SpritePowerUp in self.ListSpritePowerUps: b_collision = arcade.check_for_collision(SpritePowerUp, self.SpritePlayer) if b_collision == true: # half player movement self.right = false self.left = false self.up = false self.down = false # Graphics code to show object collision # here in a future part of this lesson. # NEW: arcade.play_sound(t_hit_sound[i]) # increment the counter. i += 1 def on_key_press(self, symbol, modifiers): # When a key is pressed: # Tracking only the four arrow keys # NOTE: We are careful to NOT use elif here # because we want to allow diagonal movement. if symbol == arcade.key.right: self.right = true if symbol == arcade.key.left: self.left = true if symbol == arcade.key.up: self.up = true if symbol == arcade.key.down: self.down = true # NEW code in this chapter to handle Load Game and Save Game if symbol == 108: # they pressed "L" gameLoad() # Redraw screen, etc. main() elif symbol == 115: # they pressed "S" gameSave() def on_key_release(self, symbol, modifiers): # When a key is released: if symbol == arcade.key.right: self.right = false if symbol == arcade.key.left: self.left = false if symbol == arcade.key.up: self.up = false if symbol == arcade.key.down: self.down = false Def main(): # Primary module getScreenFromDB() db_cursor = getObjectsFromDB() gameWindow(i_width, i_height, t_title, db_cursor) enemyMovement() arcade.run() |
Conclusion
In this part 8, we continued creating a 2D game with Python and Postgres and Save Game as a “chapter” in a multi-section series of lessons where the final result is a top-down-view Pac Man-like video game where the goal is to “eat” powerups and avoid monsters. We used the Arcade library for Python because of it being a modernized version of Pyglet. We used Postgres to read and write screen and objects such as the enemies, obstacles, and power-ups. In this lesson we added Load Game and Save Game via the “L” and “S” keys. In future articles we will add user id creation, multi-player, and a screen editor.
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