Sep 28 2011

Loading RIC files from a byte stream

Category: Lego,Mindstorms,RICcreator,SoftwareSpiller @ 17:48

riclib have until now read RIC files directly from a file stream. This is done using a distributed approach, each nxtVariable is passed a file stream pointer and loads the data it needs by itself.

A ricfile in riclib is made up by an array of ricObjects which each contains a list of nxtVariables containing the data. When a ricfile starts loading, it reads the first 4 bytes which contains the ricObject header and creates the ricObject which have the same opcode as specified in the header. That ricObject read funciton is then called, loading each of the nxtVariables it has. The whole process is then repeated untill it is not possible to read another header.

Adding a second source to read from would require an extra read command to be added for each nxtVariable which would be a lot of work.

A file can easily be converted into a char array, so I could just drop direct file reading and rewrite every function to read from a char array instead. Actually, I should have done this from the start. (I didn’t because this would require 3 paramters to be passed each time, the char pointer, the current position in the array and the total lenght of the array.)

I decided of some reason to do a more complicated approach. I added a abstract base class nxtIO which is used by nxtVariable to read and write to RIC files. I have then added to classes which inherits nxtIO, nxtFile which implements file IO and nxtStream which implements IO on a char array. The advantages of doing it like this is that I only need to pass one parameter, the nxtIO pointer, and that it is possible to add several other types of IO without redoing the reading functions in nxtVariable. The disadvantage is that it is more work and that I probably will not need to be able to read/write from anything else than char arrays anyway…

The reason behind using byte streams

One of the key goals with riclib and the reason it is keept seperate from the GUI code is that it should be easy to use it to extend other applications to use RIC files. However since it needed a RIC file containing the font to use with TextOut to be located together with the exe this could complicate matters for the application developer.

So one of the key benifits with reading from a byte stream is that a RIC file can be embedded into the exe. IO to a byte stream can be used in the other direction too, in order to create a C header file containing a RIC file to easily embed the RIC file into C/C++/NXC programs. (quick implementation done)

Another important reason is that when you use riclib in other applications you might not be able to read/write directly from/to a file. Consider that you want to upload and download RIC files to the NXT. The interface functions will undoubtly use byte streams instead of files. (I will add this feature as soon I as can figure out how to do it.)

Another case would be using riclib together with the Windows Shell. Once I figure out how to create a COM module I’m planning to add RIC support into Windows Explorer. While supported, Microsoft discourages using filepaths and suggests accepting and using bytestreams instead.


I’m currently creating an image viewer using QT. QT already supports most image formats like JPG, PNG, BMP, SVG and more, but allows you to create plugins to implement special fileformats. So I created a plugin to extend QT to support ricfiles using riclib. This will not just extend my application, but every QT application using QT’s inbuilt image functions. (The application and plugin will be posted in the near future.)

I will not go into depth about how this is done however one of the key aspects is that QT is not using filepaths, but its own QIODevice class which does a similar task as my nxtIO class. I could create a sub-class which inheriths nxtIO and read/writes to a QIODevice, but I took the easy solution and just used the QIODevice to read the whole file in one go and use nxtStream instead.

QByteArray data = device()->readAll(); //Read all bytes in QIODevice into data
nxtStream stream(, data.size() ); //Create a nxtStream using data
ricfile file; &stream ); //Read the RIC file

nxtStream takes a char pointer and a int holding the size of the array. What is left is just drawing the file:

nxtCanvas canvas;
canvas.set_auto_resize( true );
file.Draw( &canvas );

The canvas is created at size 0x0 with auto_resize on. The RIC file then draws on the canvas, expanding it as needed.

The next step is to convert the nxtCanvas into an image format the application supports which is normally rather trivial. One thing to remember is that (0,0) is located in the lower left corner in nxtCanvas where it is most often located in the upper left corner in other formats.

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