How I Learned Python

Being primarily a C++ programmer, I have lived a hard life: All the rules, all the syntax, all the mean spirited compiler errors from the STL...

While I have dabbled in scripting languages in the past, I never really put too much time into learning one. I decided it was time to learn a scripting language in more detail, and I chose Python. The best way to learn a new language is to create a relatively complex program in it, so to accomplish this task, I set out to make a game in no more than 7 days using Python and PyGame (SDL wrapper). Being familiar with using SDL from C++, I felt confident this project would be a success, and it was. 4 days later, I had a new game, "Cloud Cover", and I knew a decent amount of Python. Here's how it happened.

Game Design

I had been toying with an idea for a game that involved the rain theme for quite some time. Originally, I wanted to develop the game for the iPhone and take advantage of the tilt-control. The idea at that point was to tilt the iPhone left and right to tilt platforms in order to fill up buckets with water in order to progress in the level. However, not particularly liking Objective-C or the hoops needed to jump through in order to develop for the iPhone, I nixed that idea.

After hearing the instrumental "2 Die 4" by 'John 5' and then going to sleep, I awoke with the game design in my head. It literally came to me in my sleep. In fact, I even feature the song in my game because it fits so well (and it should since it inspired the game!).

Essentially, the game design is as follows:

• You play the part of a bowling ball who must fill up beakers with rain drops.
• On each level, you will have either 1 or 2 beakers to fill, and they may be positioned with at most 1 beaker on each side of the player 
• The game will only have 2 controls: roll left and roll right. This adds to the challenge of the puzzles because you can only move each beaker in 1 direction.
• Rain is created by a dynamic rain system from 1 or 2 clouds per-level.
• The clouds can be configured to behave in many different ways, such as: being stationary, moving left/right (single or multiple passes), being restricted to certain x-value bounds, having endless rain drops, or having a limited supply of rain drops.
• Tweaking the dynamic rain system along with the placement and movement of the cloud(s) and beaker(s) can be used to create challenging puzzles

Implementation

Dynamic Rain System

Implementing the dynamic rain system was a lot of fun, and a lot easier than you may think. Basically, it boils down to this:

• Assign each cloud a life span (number of drops it can produce)
• Assign each cloud an intensity value (number of drops it produces per-frame)
• Using the dimensions of the cloud, generate a random x,y coordinate at which to generate a new rain drop within the bounds of the cloud.
• Generate the rain drops in a loop ranging from 1 to the intensity value
• For each drop created, subtract 1 from the life span of the cloud
• As long as the life span is > 0 (or the cloud has an infinite life span), continue to generate rain

Pretty simple, eh?

Beakers

There were a few things I had to deal with when implementing the beakers. First, I wanted to have some sort of physics effect so that the character would be slowed down while pushing them. I decided to fake the physics first and see how well it worked before implementing the real deal. I got lucky on my first attempt at this. I gave each beaker a fractional weight value (settled on .5). Then, on collision, I would multiply the player's speed by the weight of the beaker. Since it is a fractional value, it would decrease the player's speed by a factor of the beaker's weight. The result is a very believable friction effect. Sorry, Newton, I don't need you today...

The next issue with the beakers was getting them to "fill up" as they caught rain drops. This one took a little bit more time to nail down, but I'm pretty happy with the solution I came up with. Basically, each beaker keeps track of how many drops it can hold, and how many it's already caught. Using these values, combined with the height and width of the beaker, I do some simple division to create a fill percentage and draw a filled rectangle inside the beaker. This gets updated on every game update, so as you collect more drops, the box grows taller and taller, thus the beaker appears to be filling up. Until the beaker is full, the box is the same color as the rain drops, and once full, it turns red so the player knows to stop trying to fill it. Some normalization had to be done for when the beaker does fill up, as well as to account for leaving some space on the sides, but the code for this is pretty straightforward:



I did have to address one issue with the beakers in that they were detecting "caught" drain drops anytime they collided with a rain drop. Clearly, you could collide with low-falling drops by pushing the beaker into them, but that's hardly catching them, so it had to be fixed.

See this post for details on how I went about that.

Player

The player is a fairly simple piece of code, although there is one neat trick I employed. I was faced with the question of, "How do I make the bowling ball roll around?". Sure, I could do some involved math to do it, but I'm just using a static image for the player character. So, what to do? Rotate the image!

Conclusion 

All in all, the game took around 4 days, but probably only about 15-20 hours of time. It was essentially the first non-trivial program I had ever written in Python, and it turned out really great if I do say so myself.

You can find the game here

                         

 

Just A Drop In The Bucket (or was it?)

I had a known bug in my new game, "Cloud Cover" which involved detecting a "caught" rain drop when the drop actually hit the side of the beaker instead of in the opening. I knew about the issue, but due to the mechanism I was using to detect collisions (a pre-made function from the PyGame library), the solution wasn't immediately apparent. It would have been difficult and clunky to adjust the iteration on each collision detection to then ensure that the drop that had been detected as a collision was in the acceptable range, being y <= the top of the beaker (y increases towards the bottom of the screen).

So, after some thinking, I came up with the following solution: Instead of checking the y-value of the drop once a collision is detected, only check for collisions against rain drops that are within the acceptable range. It works great, and it's pretty slick if I do say so myself.

First, I store the heights of all beakers in the current level. Currently, each level has at least 1 beaker, no more than 2, the beakers exist for the duration of the level, and they are all of the same height. However, in the future this may change, and beakers may even be destroyed as the level plays on, so I had to ensure that I was able to keep track of the beakers that were currently on the screen: having a static list of the beakers that the level started with wouldn't have been sufficient. Then, I sort the list of beaker heights. This ensures the smallest beaker height will be in the front of the list. This is crucial because I need to use the y-value of the *smallest* beaker as my baseline for accepting collisions because even if I have taller beakers, a y-value of <= the smallest one will also suffice for any beakers taller (remember, y gets larger as it approaches the bottom of the screen). Now that I have the y-value of the shortest beaker, I check against this value when a collision is detected. If the rain drop's y-value is <= this number, I know it is within the area of the opening of the beaker, and I can consider that a collision, and thus a "caught" rain drop.

This also has a nice benefit in that it eliminates a number of otherwise useless and costly collision comparisons. Before, every drop on the screen was being checked for a collision. Now, any drop that is below the shortest beaker is ignored entirely. With enough drops on the screen, this can be a big savings in performance.

The code for this is as follows:

Game In A Day - "Hangman"

The second installment to my Game In A Day series is a project I started many years ago, and have maintained in not-so-consistent fashion: Hangman.

I wrote this about 5-6 years ago in C++. The interface was console-based only and this lead to a lot of added headaches and bugs. I've been meaning to throw a GUI on this project for a while, but just never got around to it... until now!

As part of my Software Engineering capstone, my group and I are making a set of educational games to teach 4th and 5th grade curriculum in Math, English, and Reasoning Skills. The English side of things was lacking a bit, so I decided to create Hangman in the context of my capstone project. Note that at the time, there were only 4 weeks left in the course and we had moved every other project into their final phase. So, if Hangman was to be added, it would definitely have to be developed in less than 1 day!

Interface Design
I came up with the design in a fairly short amount of time while I was sitting in one of my morning classes. Obviously, Hangman is a classic game and interfaces for it can only vary so much, but I did add a few tweaks. First, I designed it so that the vowels and consonants are displayed to the user in horizontal list form. This assists in the curriculum for the target audience as they can learn to identify the different letters as well as learn the words and definitions. Second, guessed letters (both correct and incorrect) get removed from their respective lists. This helps the player keep track of what they've already guessed and what's available to guess. Last, I added a "Solve" button to the interface so that at any time they can choose to solve the puzzle.

Game Design
Much like the interface design, the gameplay for Hangman is relatively set in stone. The flow that I went with is as follows:

• A definition is displayed to the player
• Below the definition, a series of _ characters are displayed to the player to represent the number of letters in the answer
• When the player types a letter, the game checks to see if that letter is in the puzzle, and if so, replaces each corresponding _ with the guessed letter.
• A wrong guess results in the next Hangman image being displayed to the player on the interface. The images are looked up using the number of questions wrong as the index into the vector of images. In total, there are 9 images, and the game is over when you've missed 9 questions.
• At any point the player can choose to hit "Solve" and try to solve the puzzle. An incorrect guess results in the player losing.

Pretty simple, eh?

Tools
I decided to use C++ and QT for this project because I'm very familiar with QT and it is an incredibly powerful library.

Implementation
Instead of adding a GUI to the pre-existing code I had, I decided to write the entire game from scratch. Using QT made this quite simple, actually. It allowed me to use the built-in QT types for everything (QString, QChar, QVector, etc...) and keep the code clean and consistent. You would think that writing a game entirely console-based would be easier, but when you have to deal with validating user input, alternating between std::string, char*, and char, things get messy in a hurry. Also, organizing game flow and game state create equally messy situations. A GUI environment like QT eliminates this mess with the use of dialogs and events to properly handle flow and state changes.

All in all, the implementation was fairly straight forward and consisted of the following pieces:

• Event handler to grab alphabetic input (ignores all other input)
• Function to check if a letter exists in the answer (and every location in which it does)
• Function to handle solving the entire puzzle
• Function to remove the last guessed character from both the vowel and consonant lists.
• Functions to handle a correct and incorrect guess
• Function to handle the end of the game
• Function to handle resetting the game to the initial state

That's it. Total, the project only took around 5 hours from start to finish, so I'm very pleased with that result. The only thing left to do is to plug it in to our QuestionManager to dynamically grab pre-made questions.

Notable Code Snippets

Determining If Input Is An Alphabetic Character



Finding Every Occurrence Of A Letter In A Word