http://freespeech.sourceforge.net/overflow.htmlOverflow is a free (GPL/LGPL) ``data-flow oriented'' development environment. It can be used to build complex applications by combining small, reusable building blocks. In some way, it has similarities with Simulink and LabView, although it is not designed (and far) to be a "clone" of any of them.
Overflow features a GUI that allows rapid application development and includes a visual debugger. Although Overflow can be seen as a rapid prototyping tool, it can also be used for building real-time applications, such as audio effects processing. Since overflow is not really an ``interpreted language'', it can be quite fast.
It is written in C++ and features a plug-in mechanism that allows new nodes/toolboxes to be easily added. Overflow currently includes the following toolboxes:
Overflow was designed with the following goals in mind:
This section defines the concepts and terms used by Overflow and shows how they relate to C or Matlab constructs.
The basic processing using in Overflow is a Node, a Node is in all ways similar to a C or Matlab function. It takes some input data, performs some operations and send data out.
A built-in Overflow node is written in C++ and is part of the Overflow code (or compiled in an Overflow toolbox, like Matlab's .mex files). In Overflow, all nodes are implemented as a class that derive (directly or indirectly) from a base class called "Node" (note that most nodes derive from "BufferedNode"). Although the Overflow implementation of different nodes uses C++ inheritance mechanism (using classes), there's no reason for the user to be aware of that. For that reason, it's not recommended to refer to nodes as "types" or ``classes'' (e.g.. if Overflow were written in C, nodes would be implemented as functions).
An Overflow sub-network (or subnet) is a collection of connected nodes that can be used as if they were a single node. Most Overflow subnets will be saved into .n files, which are almost the exact equivalent of Matlab's .m files. There's no real C equivalent because C is a compiled language (although it could be seen as a C function calling other C function).
The inputs of an Overflow nodes are equivalent to the arguments to a Matlab/C function. The same for outputs, but while C is restricted to one return value, Overflow and Matlab can have several outputs. Node inputs and outputs are sometimes referred to as ``terminals''.
Overflow node parameters are also equivalent to C/Matlab function arguments. The difference between node parameters and node inputs is that parameters cannot change at run-time. They are specified at "build-time" and stay constant throughout the run. For instance, the "Constant" node has no input, but has a parameter called "VALUE" that is returned as the output of the node. Using constants, you can always "transform" another node's input into a parameter (to the constant). The reverse is not true, however. Why then have parameters and not define every argument as an input? Mostly simplicity and run-time performance. Sometimes, it is just a lot easier to know certain arguments in advance and be sure that they don't change during the run. However, when possible, it is better to implement arguments as inputs, as this allows more flexibility.
There's no real correspondence between Overflow links and C or Matlab constructs. The best analogy would be to say that Links represent the order of the lines in a C/Matlab function. You also need to keep in mind that Overflow uses a "pull method" in order to compute data. What does that mean? When you run a network, the last node (output node) of the main network (called "MAIN" - how original!) is asked for its output. In order to compute its output, it needs to ask its input nodes for their output. That way everything propagates from the end to the beginning recursively.
Now, why going backwards like that? That's a bit long to explain. The quick answer is "because". The longer answer involves faster handling of dependencies, faster processing, buffer management and things like that.
Unlike Matlab, that only supports the complex-double-matrix type (well, that's not totally true, but...), Overflow (like C and C++) has support for many different types. The ``basic'' Overflow types are: Bool, Int, Float, Stream, String and Vector. There are also toolbox-specific types, like FFNet (neural network), VQ (Vector Quantizer), GMM (Gaussian Mixture Model), ...
Right now, the only way to define a new type in Overflow is by adding C++ code for it in a toolbox (or the core). Eventually, there will (could?) be a way to pack data in a "struct" using Overflow nodes, but this is not implemented yet.
Some Overflow Nodes expect a certain type of data as input/parameter and will generate a run-time exception (which will abort execution) if the wrong data type is used (e.g.. a Load node expects a Stream as input and nothing else). Some nodes, like the NOP (no-op) node, can take any type as input. Some node have more complex behavior, like the Add node that can add two floats, two Vectors of the same dimension, but cannot add a Bool and a Vector.