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I am interested in finding a good c++ library (or base code upon which to create one) to draw interactive connected graph components in Qt.

By connected graph component, I mean graphs whose nodes are components with input and output sections in the style of graph nodes in Blender Node Editor or Grasshopper, see example.

By interactive, I mean that I need to be able to access the component position and locations to let the user select and interact with them.

My requirements:

  • for Qt in C++
  • least amount of external dependencies (best would be just a header library)
  • support for automatic layout (or semi-automatic, the nodes being set, the edges having to be connected automatically)
  • interactivity-enabled (i.e. not just an image output, most likely based on QGraphicsScene)

My current implementation is using GraphViz with QGV but it only support simple component nodes (no specific input / output elements). While GraphViz supports record and html elements, QGV doesn't and it looks like a sufficient hassle to implement it within a fork of QGV correctly given the constraints from GraphViz that I wonder if there is no better choice, trying to not use GraphViz.

I could also be fine with a simple non-graphics library that does the layout given size constraints and relative position constraints (the component blocks have a fixed size, the input/output nodes positions are fixed given the location of the component block).

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Maybe too late but still here is the library I develop for general-purpose node graph editing.

https://github.com/paceholder/nodeeditor

Key Features:

  • Based on Qt 5.x with C++14
  • Based on QGraphicsScene
  • Nodes are behaving according to user-defined models
  • No dependencies (just Qt).
  • Different color styles

Check the video to see what the library is capable of: 1

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  • It is a bit late for me to use it for the project I was planning it for, indeed, but it's worth having it mentioned somewhere. I may look at it if I happen to need it in a new system. Do you know how well it scales to larger graphs? I'm talking about a few hundreds of nodes, which is quite common for algorithm-based systems. One I found out about later (but in Python is that of Antimony, a Media Lab project for CAD, mattkeeter.com/projects/antimony/3), and it seems to scale up to some level.
    – Alexandre Kaspar
    Commented Dec 19, 2016 at 19:46
  • 1
    In terms of the graph rendering performance it scales pretty well as it is based on the super-fast QGraphicsScene engine. If we talk about signal propagation, I assume it must be a little slower than a Python script (for example). Internally I use std::shared_ptr to wrap user's data and to pass it to the next model. This requires some memory allocations and shared pointer copying. Anyway, one guy managed to make a real-time GLSL renderer based on this Node Editor with a dozen of primitives that delivered 30-60 FPS (github.com/v0q/CollaborativeResearchProject)
    – paceholder
    Commented Dec 20, 2016 at 21:35
  • This is exactly what I've been looking for, absolutely stunning! @paceholder
    – Moia
    Commented Mar 5, 2019 at 11:08

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