John's Clicky Turtlehack

Man, do I hate Python sometimes.

I decided that I wanted to make a Frogger clone for this week. I loved Frogger as a kid, and I fondly remember spending hours trying to beat it on my grandparents’ ancient HP CRT hooked up to an equally ancient HP tower. Not sure why they were so fond of Hewlett-Packard, but I can’t remember them ever having a different brand.</br>

Anyway, things went about as well as expected. My ‘final’ product for now is a screen with a moveable turtle that has a goal zone and prints “VICTORY!” when you enter that zone. No obstacles, and the only scenery is a couple of roads (of which I am damn proud, by the way).</br>

So, I’m going to walk you through all the frustrating bits and show off my results at the end.</br>

Streets are hard, man.

I assumed that drawing two black rectangles the width of the screen with some white stripes down the middle would be an easy, not-in-any-way-Herculean task. My bad, Python. After much struggle, this is what I came up with to draw some decent looking streets without hard coding each part:

# Draw a street
def draw_street(turtle, y, width, height):
  # Draw streets
  turtle.color("black")
  turtle.penup()
  turtle.goto(-250, y)
  turtle.pendown()
  turtle.begin_fill()
  for _ in range(2):
    turtle.forward(width)
    turtle.left(90)
    turtle.forward(height/5)
    turtle.left(90)
  turtle.end_fill()

  # Draw lanes
  turtle.color("white")
  turtle.penup()
  turtle.goto(-250, y + height/10)
  for _ in range(25):
    for _ in range(2):
      turtle.pendown()
      turtle.begin_fill()
      turtle.forward(width/50)
      turtle.left(90)
      turtle.forward(2)
      turtle.left(90)
      turtle.end_fill()
      turtle.penup()
    turtle.forward(20)

I know, beautiful, isn’t it?</br>

Sarcasm aside, this is around when I realized that drawing things in a four-quadrant cartesian plane is a little irritating. I thought the world would be all positive, with (0, 0) at the bottom-left corner and whatever the max for both axes is at the top right. Somehow, somehow, I did not realize that the setup() function has the ability to do this until I was 99% finished. That is my first refactoring goal, as seen here in my to-do list:

# XXX 1. Create a background image of several parallel streets
# XXX 2. Create a moveable player character
# TODO 2a. Refactor using setup() to make the coord plane only first quadrant
# TODO 3. Create moving enemy characters
# TODO 4. Detect collision with enemies
# TODO 5. Create buttons for menu
# TODO 6. Create Alternate map / enemies
# TODO 7. Create multiple levels

As a side note, I recently learned how to make checkboxes in Markdown. That list would look like this:

1. Create a background image of several parallel streets
2. Create a moveable player character
2a. Refactor using setup() to make the coord plane only first quadrant
3. Create moving enemy characters
4. Detect collision with enemies
5. Create buttons for menu
6. Create Alternate map / enemies
7. Create multiple levels

Anyway, on to my next topic of suffering.

Wow, onkey events can be weird.

I didn’t have too much trouble coding player movement. I originally had the right and left moves just rotate Frogger (or Turtler?), but I decided that just moving left or right would be easier on the player. All of that looked like this:

# Define player movement
def up(screen, turtle):
  turtle.setheading(90)
  turtle.forward(50)
  screen.update()
  if turtle.ycor() > 200:
    turtle.goto(-2, -225)
    turtle.write("VICTORY!", align="center", font=("Arial", 20, "bold"))
    turtle.goto(-2, -175)
    screen.update()


def down(screen, turtle):
  turtle.setheading(90)
  turtle.backward(50)
  screen.update()

def left(screen, turtle):
  turtle.setheading(180)
  turtle.forward(50)
  turtle.setheading(90)
  screen.update()

def right(screen, turtle):
  turtle.setheading(0)
  turtle.forward(50)
  turtle.setheading(90)
  screen.update()

That bit about writing “VICTORY!” in the up function is essentially a placeholder for now, but I’ll get to that. This all worked fairly well from the beginning, so not too bad. The hard part was getting it to work with onkey events. I assumed that it would be as simple as passing a movement function to the .onkey() method. I didn’t realize that .onkey() can’t accept functions with arguments normally. So, after a good bit of research, I found the lambda function in Python. That solved my problem, and all of my key events are working now:

# Let player move with arrow keys or WASD, exit with Esc
screen.onkey(lambda: movement.up(screen, frogger), "Up")
screen.onkey(lambda: movement.up(screen, frogger), "w")

screen.onkey(lambda: movement.down(screen, frogger), "Down")
screen.onkey(lambda: movement.down(screen, frogger), "s")

screen.onkey(lambda: movement.left(screen, frogger), "Left")
screen.onkey(lambda: movement.left(screen, frogger), "a")

screen.onkey(lambda: movement.right(screen, frogger), "Right")
screen.onkey(lambda: movement.right(screen, frogger), "d")

screen.onkey(bye, "Escape")

Click events were even weirder, since they have to us the click’s x and y coordinates as arguments. That took another while, but I finally got my turtle to change color randomly on click:

# Change player character color on click
colors = ["green", "blue", "red", "black", "white"]

def change_color(x, y):
  if x < 1000 and y < 1000:
    frogger.color("black", colors[randrange(0, 5)])
  else:
     frogger.color("green")
  screen.update()

screen.onclick(change_color)

Part of the problem was the weirdness with four-quadrant cartesian coordinates not seeming to work the way I think, but I found a work around by setting the values higher than the max on screen, so this guarantees a roll on the color table each click.

Turtle.pos() doesn’t want to work for me.

For some reason, every time I tried to code in the victory condition, I created a memory leak and the program crashed. I was following suggestions found online, and I’m still not sure what I was doing wrong. But, awarding the victory screen anytime Frogger gets above a certain y-value seems fine, so I’m okay with the way things currently work. Basically, if you get Turtler past the last road, you win. Simple enough.

Next steps

I really need to get the enemies (cars) working. Right now, I have created the world’s least interesting turtle simulator. So, my next priority is getting cars to move around on the roads. After that, I need to make sure that touching a car kills Turtler. Poor little guy. Not sure how I’m going to accomplish this yet, but I’ll figure it out.

The prototype

Okay, finally, here’s the trinket with my current version. You can use the arrow keys or WASD to move, and clicking will roll and random color for Turtler. Have fun.