Tilemap bitmasking

As a game developer, bitmasks are useful when it comes to representing a set of data with single digit in both 3d and 2d games. An illustration of this in use in three dimensions can be found within the well known voxel game minecraft. The current status of a block may be represented with a bitmask value to indicate whether it is open or closed when considering blocks adjacent to it. For a given voxel if one (or however many) side(s) is open but surrounding sides closed, perhaps you wish to show a grass texture or only render one side – that voxel would have a bitmask value based on what surrounds it and we can use that to determine how it should render.  If the voxel is completely surrounded, it has a different bitmask value and perhaps you wish not to even render voxels with a bitmask value that indicates it should not be visible. In this usage scenario, what this bitmask value tells you is whether the voxels on each side are open or closed – and this is all saved with a single bit. In other words, through a single bit you are storing a set of data that would otherwise require more memory!

In a 2d game this has all sorts of usage scenario’s too. For example, when it comes to tilemaps and placing tiles there is a huge benefit to storing data represented as a bitmask value. For example, a fence – having a single fence tile may have a stand alone sprite to display, however, placing two fence pieces beside each other may require two different tiles drawn to line up. This means that an algorithm will have to determine the surrounding sides to decide which fence piece should be rendered (i.e. an end piece, middle piece, L shape, etc). We can use a simple calculation to determine this for a 2d tilemap:

With this simple equation, we will then know which tile to display. Below you can see it in action in my game Attack of the Dead – I’ve replaced the wall tiles with some dummy tiles to show the bitmask value for illustration. The variables left, down, right, and up are simple boolean values to indicate whether there is a tile at these positions surrounding the tile you are calculating for.

The textures to display the tile may be named according to the bitmask value for easy organization, or alternatively, you may assign a tile to display based on the bitmask value of that tile and organize your atlas based on the bitmask value.

If you need a quick 4 tile bitmask chart, I’ve thrown one together on JSFiddle below. You can easily modify this for using 8 tiles or whatever suits your needs.

RijndaelManaged, AesManaged, and AesCryptoServiceProvider – SimpleAccountLocker App

I recently wanted to write a small app to become more familiar with .NET encryption/decryption libraries. As a result, I created a quick little account locker app which stores manually entered account data locally. Sure, there are great services available which do this already and automate the process, i.e. last pass, for saving passwords securely across multiple devices – however, SimpleAccountLocker is an extremely minimal app which provides the basis to store data locally if you do not wish to save off-site; likewise, it was a fun little way to play with some security libraries.

You can view the app on my GitHub: https://github.com/MrChrisHammond/SimpleAccountLocker

To begin, .NET offers many different encryption classes, however, for this app’s purpose, the main AES classes I tested out include:

– RijndaelManaged
– AesManaged
– AesCryptoServiceProvider

All three of these are based on AES – a specification for encryption created by the US National Institute of Standards and Technology (NIST) in 2001. This method of encryption is symmetric and allows data to be encrypted and later decrypted with a key and initialization vector. This is helpful when you have data you wish to store securely but have a later need to decrypt and read it – for example, an instant message. Nonetheless, within the aforementioned classes are a few differences. For instance, RijndaelManaged allows you to set a different block size whereas AesManaged maintains the same fixed blocksize of 128 so-as not to compromise security. However, AesManaged is actually based on RijndaelManaged.

In terms of compliance, AesCryptoServiceProvider uses a library which is FIPS compliant1 whereas RijndaelManaged and AesManaged do not.  If you are not familiar with FIPS, you might be wondering – what is it? The Federal Information Processing Standard is a set of rules which sets the requirements on approving cryptographic modules. Although this is a US government standard, here in Canada the Communications Security Establishment (CSE) uses FIPS 140-1 and 2 as part of its certification2.

In code, all three of these can be used to encrypt data with an ICryptoTransform transformation, CryptoStream decorator, and using a key and Initialization Vector (IV). Below is a  comparison of AesCryptoServiceProvider vs RijndaelManaged within SimpleAccountLocker.