Unity Tutorial – Basic Stuff

In this post I’ll show the most basic usage of the Unity3d game engine, using the C# programming language, its syntax is very similar to Java.

I’ll be using public domain assets that I downloaded here.

And instead of using the default cube of Unity, I’ll use this one, because it’s made out of Quads (like a plane, you can only see it from one side), and it’s easier to add the textures to it (I don’t know how to use blender and stuff).

Ok, so now open Unity (which you can download from it’s page), and create a new 3D project, by default, it only has a camera.

So, the Editor has windows, and you can move them around, you can add new ones in the Window top menu. The ones I’ll need are Game (here you see what the cameras are projecting), the Scene (where you edit the game), the Inspector (where you see the selected object’s properties), the Hierarchy (where you see and select objects in you scene), the Project (like a file manager), and the Console (here you see errors and warnings).

In the Project and Hierarchy windows, there is a drop-down button that reads: “create”. when you click it, you will see a lot of pre-build thing that you can use in the editor, and whatever you crete, it will appear inside the window where you clicked “create”. When I say “create something in bla”, I mean that you should click “the” bla button in this drop-down, inside the “something” window.

crearProyecto

Extract the and drag and drop the PNG folder into the Project window. Make sure you organize your files. Create these folders (right-click > create > folder):

Capture

In the Hierarchy window click on Create > Light > Directional light, this light is behaves like a sun, it doesn’t matter where you put it, only it’s rotation.

LightPut the Cube.prefab file in the Prefabs folder (does it makes sense?) and then drang and drop that weird thing to the Scene window, you’ll that the cube appears magically in the Scene, and also, the cube is added to the Hierarchy window.createCubeTile

Open the Tiles folder in the PNG folder, now, if you drag and drop the images in the cube that’s in the scene, you can assign that texture to the side of the cube where you drop the image (and that’s the reason behind the special cube prefab). You can see that, in the Hierarchy, there’s an arrow next to the cube, if you click that arrow, you will see it’s children.

GameObjects can have children, which are also GameObjects. Children have a relative position to it’s parent, and they can be easily referenced from a script. For example, you can have the “player” object, and a “gun” object. You want that gun to be a child of you player, so it’s always, in it’s hand.

GrassTile

Now add a RigidBody to the tile, this will allow the tile interact with other objects, and also, deselect the “use gravity” button.

RigidBody

Once you’ve done this, go to the Prefabs folder and (in the Project window) click on Create > Prefab. Now, drag and drop the Cube (in the Hirarchy window) to this new Prefab in the Project window. As you can see, the cube is “inside” the prefab. you can now delete the cube from the scene.

A prefab is the way Unity defines custom Game Objects, so that you can instantiate them, without the need to create them again, so it’s very similar to creating a class when you are programming (but of course, it’s not the same).

create an empty game object in the Hierarchy, and name it, I don’t know, map, or terrain, or whatever, then go to the Script folder and create a new C# script, we’ll use this script to automatically generate the terrain, based on the tile I’ve just created, when the game is loaded. drag and drop this new script to the empty game object in the Hierarchy.

Every GameObject you create has different fields, if some field is set to public, it will appear in the Inspector window, you can change the values of these properties inside the Inspector.

createTerrainGen

Everything in Unity is a GameObject, which is a special class of Unity, and every GameObject has at least a Transform. a Transform determines the position and rotation of that object in the scene.

If you double click the script you’ve just created, the code editor should be opened (Visual Studio or Monodevelop).

unityCodeExplain

The C# syntax is very similar to Java, but to implement and interface you write <ClassName> : <InterfaceName>.

Monobehaviour is a special interface of Unity, if you delete that, you will not be able to attach the script to a game object.

In Unity Scripts, there are special method names,  the Start method is called when the GameObject is instantiated and the Update is called once every frame. You can search for more special names in the Unity documentation.

add these fields, you want them to be public so you can change them from the Unity editor. the grassTile of type Transform will hold the prefab I created earlier. the tileSize is set to 1 by default, but you can change it from the editor. You need to drag and drop the tile prefab we created to the Grass Tile field that you can see in the Inspector when the Terrain object is selected.

There are Vector2 and Vector3 classes, and they are what you would expect.

publicthings

Now add a Vector2 called terrainSize and these for loops:

fors

I’ll create a plain terrain for now, the terrainSize represents the amount of tiles with size = tileSize. These for loops will “walk” through a “grid”, in each position a new tile will be instantiated:

instantiatingtiles

This is a static method in the GameObject class that creates the specified object in the scene (and you can instantiate almost anything, because everything is a GameObject). It returns the instantiated object, and we can tell C# to convert it to a Transform (because aTransform is a Game Object, and you know, “polymorphism” stuff).

You can change the values of the public fields that you declarated in the script:

changethings

You should see something like this in the Scene window.

result

Anuncios

#WSQ09-TheMovies

See the assignment on github.

This assignment has been the hardest so far, I had to read a lot of documentation to complete this one.
I had to learn about these things:

  • About the Scanner class, for reading files and receiving input from the console.
  • About the Set interface and HashSet class, to use it like a dictionary in Python.
  • About the Map interface and HashMap class.
  • About how the String class operates and some methods.
  • About CharSequence, just because String is an implementation of CharSequence.
  • About handling Exceptions, for the file reading and the MovieQuery class.
  • And finally, a little bit about regular expressions, for reading the query.

So when I read the the document in the link of the assignment, it says that we need to do set operations, and I found this on stack overflow.
It turns out that I didn’t need to implement any of the code for set operations, just imported the Set interface and the HashSet class.

SetMethonds

 

The Set interface contains the methods addAll, retainAll and removeAll, which are equivalent to union, intersection and difference set operations, respectively. But the problem said: find the set of actors that the given movies don’t have in common. (or something by the way).
And so, this is equivalent to the difference of the union and the intersection of two sets. (A ∪ B) – (A ∩ B). And this is called the symmetric difference.

So I first created the Movie class and wrote several constructors supporting different data types, because why not. It has two fields, a String; representing the name of the movie, and a Set of Strings; representing the name of the actors. I wrote the methods for the operations I described above. It doesn’t makes much sense because it’s just returning the result of the call to the set methods, but at least I gave these methods a fancier name. But it makes sense in the getActorsNotInCommon method, because the symmetric difference is not implement in the Set interface. I also added getters and setters and bla bla bla.

Before using the File class I tested it.
throwMissing

But the code would not compile, and then, reading the docs of the File class, I realized I had to add “throws Exception” after the method parameters.
justAddthrows
And there are a lot of different implementations of the Exception interface.

In the MovieLibrary class I used a Scanner to read the file where are the actors and movies. And the constructor can throw a FileNotFoundException, and it has to, because the File class can, and so the code where it is used has to as well. The class has a field for storing the movie objects in a Map, using its name as the key, so the program has to store the name of the movie twice, and I though it was stupid, but I didn’t found a better way to do it, but now I’m wondering if it is possible to use something like a pointer to the variable inside the Movie object, to use it as the key of the HasMap, but whatever.

And the code for reading the file with the scanner:
usingScanner

In the constructor of the MovieLibrary two scanners are used, one for reading the lines of the file, and another one for reading that line and separate the actor and movies, and then instantiating a Movie object -only if the name was not already in the map- and then pushing it into that map.
This class use the methods of the Movie class in all the methods.
movieLib

And I tested what I had written up to this point, before moving into implementing the user input:
testsOfTheFinalCode

Then I was writing the main class, TheMovies, according to the description in the assignment (with the menus and option and shit). When I reached the part where says that I should ask the user for an input like: “movieName symbol moviewName”, I realized that it would be too much code, and it would be a mess with all the logic of user input, String processing and the use of the MovieLibrary class. So I decided to write another class.

In the MovieQuery class, given the description of the problem, I though I would need to use Regular Expressions somehow. I found this nice page to learn and test regular expressions.
I didn’t wanted for this class to be instantiated, and I was thinking of something like a “static class”, but it turns out there is no such thing, at least in the Java programming language, but you can simulate this behavior by adding some modifiers, like making the constructor private and some static methods and fields.
The class use a Scanner, with a regex delimiter like this: “( )|&^“. And what this is telling to the scanner is that it should identify a substring of that format, “()” means that the thing inside the parenthesis must appear in the string and the “[]” means that there must be any of the characters inside the braces. And by doing this, when I call the next() method of the scanner it returns the name of the first movie and calling next() again will return the second movie name.
When it finds the two name of the movies it searches for them in the MovieLibrary, and, if some of the movies is not there, throws an RuntimeException, because I don’t want neither keep executing the code nor return an empty Set.
It searches for which command is in the input, calls the appropriate method in the MovieLibrary instance and returns the result.
MovieQuery

And so the only thing the TheMovies class does is using the previous classes to ask and execute the user input.
TheMovies

And here’s the output produced by the command line.

output

#WSQ08-Yo Soy 196

This thing was really weird, I mean, it’s useless but it was interesting.
So a lychrel number is a special number, if the repetitive addition of a number with the number formed with inverse of its digits form a palindrome then it’s not a lychrel number.
So, in example: 196 + 691 = 887, 887 + 788 = 1575, … and so forth.

So here I first programmed the YoSoy186 class, before programming LychrelSequence and LychrelNumber, because I wanted to define how the class would work instead of programming it in the first place.
yosoy196

So because I needed to flip the digits of the numbers, I converted the number to a String. And because in this lynda Java course they said I should use the StringBuilder class to work with string, because it’s expensive to do the string operations with the normal String operators.

And then, in the Lychrel number class, I wrote a lot some fields, getters and setter then I wrote the above algorithm to evaluate if the number is a candidate to be a lychrel number:

public class LychrelNumber {
  private int value;
  private boolean isPalindromeNumber;
  private boolean isLychrel;
 
  public LychrelNumber() {
  }
 
  public LychrelNumber(int number) {
    setValue(number);
  }
 
  public boolean isLychrelNumber() {
    return this.isLychrel;
  }
 
  public boolean isPalindrome() {
    return this.isPalindromeNumber;
  }
 
  public int getValue() {
    return this.value;
  }
 
  private long[] evaluateHelper(long val) {
    StringBuilder reverseStr = (new StringBuilder(Long.
    toString(val))).reverse();
    long reverse = Long.parseLong(reverseStr.toString());
    long add = val + reverse;
    return new long[] {reverse, add};
  }
 
  private void evaluate(long value) {
    long[] r = this.evaluateHelper(value);
    String addStr = Long.toString(r[1]);
    this.isPalindromeNumber = (value == r[0]);
    if (!this.isPalindrome()) {
      for (int i = 0; i < 30; i++) {
        r = evaluateHelper(r[1]);
        addStr = Long.toString(r[1]);
        if (addStr.equals(new StringBuilder(addStr).reverse().toString())) {
          this.isLychrel = false;
          break;
        }
        this.isLychrel = true;
      }
    }
  }
 
  public void setValue(int number) {
    this.value = number;
    this.evaluate((long)this.value);
  }
}

In the code I wrote a private method, which is only called when the setter of the value is called, and another method to reverse and add these numbers. I used a long number because the repetitive addition of the numbers generated huge numbers and the program would run out of memory.

So first, before checking if the number is a lychrel number, I check if it is a palindrome, and then, if it is not, run the code to check if it is a lychrel number (because if it is a palindrome then it’s not a lychrel number). If at some point the addition of the number and the inverse of its digits is a palindrome, the code breaks and sets the isLychrel number variable to true.

For the LychrelNumber class, I used the ArrayList class to be able to append elements to the list, something you can’t do to a normal array easily. I used three lists, for storing the lychrel, non-lychrel, and palindrome sequences. The link says that since the List class is an Interface, you need to declare a specific implementation of this Interface.
All this class does is iterate from the lower bound to the upper bound, and instantiating the LychrelSequence class with that value, and if the number is a palindrome, it’s added to the palindromes list and the non-lychrel list, else, if the number is a lychrel number it is added to the lychrel list, but not all non-lychrel numbers are palindromes).

import java.util.List;
import java.util.ArrayList;
 
public class LychrelSequence {
  private int lower;
  private int upper;
  private List<Integer> lyqSeq;
  private List<Integer> nonLyqSeq;
  private List<Integer> palindromeSeq;
 
  public LychrelSequence(int lowerBound, int upperBound) {
    this.lower = lowerBound;
    this.upper = upperBound;
 
    this.lyqSeq = new ArrayList<>();
    this.nonLyqSeq = new ArrayList<>();
    this.palindromeSeq = new ArrayList<>();
 
    LychrelNumber ln = new LychrelNumber();
    for (int i = this.lower; i <= this.upper; i++) {
      ln.setValue(i);
      if (ln.isPalindrome()) {
        palindromeSeq.add(ln.getValue());
        nonLyqSeq.add(ln.getValue());
      } else if (ln.isLychrelNumber()) {
        lyqSeq.add(ln.getValue());
        System.out.println(“Found a Lychrel number candidate: ” + ln.getValue());
      } else {
        nonLyqSeq.add(ln.getValue());
      }
    }
  }
 
  public int getLowerBound() {
    return this.lower;
  }
 
  public int getUpperBound() {
    return this.upper;
  }
 
  public List<Integer> getPalindromeSequence() {
    return this.palindromeSeq;
  }
 
  public List<Integer> getLychrelSequence() {
    return this.lyqSeq;
  }
 
  public List<Integer> getNonLychrelSequece() {
    return this.nonLyqSeq;
  }
 
 
  public int getNumPalindromes() {
    return this.palindromeSeq.size();
  }
 
  public int getNumLychrels() {
    return this.lyqSeq.size();
  }
 
  public int getNumNonLychrels() {
    return this.nonLyqSeq.size();
  }
}

Something weird I noticed is that you have to use the Integer class when declaring the list, instead of the primitive type int.

onlyInteger

And the here’s the Github repository of this homework.

#WSQ07-Babylonian Square Root


First of all, the Babylonian square root is a Babylonian algorithm for calculating the Babylonian Square Root (duh…) of a given number, say n, but in a non conventional way. This algorithm consists of making a guess (i.e.: think of an approximate value to the actual square root), say g, then, you add g, to the ratio of the number and the guess, and divide that by 2.
So, this is:

Babylonian square root equation

And the result of this equation is the new guess.
We do this process several times and then the final guess is the result of the square root.

This is the class, without the method for calculating the square root.

Screenshot from 2016-02-04 12:14:39

So the algorithm says that we need to pick a near number to the actual square root. So I imported the Random class to pick some random number near the half of the number, because YOLO. Then I used that number as the first guess and executed the algorithm.

And here’s the final code.

finalwsq07

And the github repository.

#WSQ06 Greatest Common Divisor

I was not sure if I should write the GCD method by myself or if I could use an already implemented method.

Of course I read about The Euclidean GCD algorithm because I am too lazy to search it in the Tec library. And this is also interesting, the pseudo-code algorithm and a formal proof of correctness from proofwiki.

This recursive algorithm is basically a method for finding the greatest common divisor of two integers. So you take two integers a and b such that |a| > |b|, then you calculate the remainder, call it r, of a/b. Next, set a = b and b = r

And i was writing the GCD class, but then I told myself:

Why should I write this if someone else has already did?

And of course also because this class is about Object Oriented Programming and not about Algorithms, and also, that’s one of the big advantages of OOP, you can use someone else’s code without worrying if your code will be compatible with other persons’ code, because it should

And after all these philosophical thoughts I decided to keep it simple and just use the BigInteger java class I found here get gcd java and here Big Integer Class.

Screenshot from 2016-02-04 11:54:28

I also pushed it to GitHub here: WSQ06-GCD.

Screenshot from 2016-02-08 12:40:06