Introduction to Computer Programming: Lab 9

A simple graphics game

(an introduction to event-driven programming)



Your goal is to implement a very simple graphical game that uses key and timer events. The "story" for the game: the player seeks the gold treasure, guarded by the enemy. The player must reach the gold before the enemy does, before time expires and without running into the enemy. The player moves in four cardinal directions using arrow keys. The enemy moves randomly, several times per second. The player loses if it touches the enemy or if too much time elapses.


  1. Read over the the starter file and the square-graphics module. Ask questions about any parts of the code you do not understand. Experiment with running the starter code as is and contrast that with the runnable solution module.

    Out of the box, the player and goal (the "gold treasure") are displayed and the player can move to the right ("east") by pressing the right-arrow key.

  2. Write functions north(), south(), and west() and add three more onkey events to start_game so that the player can move north, south, and west. (Follow the model used for east. The relevant key names are 'Up', 'Down' and 'Left'.)

  3. Winning. Modify player_move so that if the player moves onto the same square as the treasure (g_gold), the game ends and a suitable message indicating that the player won is printed to the shell. (Call game_over).

  4. Add code to the function countdown_timer so that, assuming the game is still being played, a message is printed in the shell indicating how many seconds are remaining (the global variable g_time), the timer is decremented, and the function schedules itself to execute again one second later. (Use ontimer.)

  5. Losing - part I. Modify countdown_timer so if the time reaches 0, the game ends with an appropriate message. (Call game_over.) You may wish to adjust the initial value of g_time.

  6. Modify player_move so that the player's position only changes if it does not go outside the bounds of the graphics window. You may wish to adjust the values of ROWS and COLUMNS.

  7. Complete enemy_timer so that, assuming the game is still being played, the enemy moves randomly up to one position in both the horizontal and vertical directions. (The chance the enemy moves north, south or stays in the same row should each be equally likely; likewise for moving west, east or staying in the same column.) The enemy should move once for every ENEMY_TIME milliseconds. (So, enemy_timer, like countdown_timer should schedule itself to execute again in the future using ontimer.) Start the enemy moving by adding an ontimer event to start_game. You may wish to adjust the value of ENEMY_TIME.

  8. Add "wrap around" mechanics for the enemy: if it goes just past the right edge it should reappear on the left edge of the graphics window and vice versa and likewise for the top and bottom of the window. (Hint: use the % operator.)

  9. Losing - part II. Modify player_move and enemy_timer so that if the player moves into the enemy, the enemy moves into the player, or if the enemy moves into the gold, the player loses.

  10. Experiment with different values for the countdown clock, the dimensions of the graphics window and the speed of the enemy to make the game suitably difficult.

Time permitting