It is similar to the original Mondrian and the Mondrian from Roassal, but it is different in that it is built directly out of Bloc elements. This is interesting because it allows us to combine typical widgets with visualizations. The other interesting thing about it is that it validates the design of Bloc: right now, the implementation has 509 lines of code (excluding graph-specific layouts). The goal is to make visualization a first class citizen and an integral part of the IDE.
The key ingredient that made this happen is that Bloc can now treat graph layouts, such as tree or force based, behave under the same rules as typical widget layouts, such as grid or flow. The challenge comes from the fact that a graph layout depends on the notion of edges between elements, and we did not want to have elements know about edges in the core of Bloc.
Thus, edges form constraints, and constraints are what layouts deal with. That is one reason why elements in bloc have the ability of defining layout-specific constraints. Using this, we can nicely define edges between elements as a plugin to Bloc, but still be able to connect arbitrary elements. What’s more, it turns out that we need constraints for other layouts as well. For example, an element in a grid layout might specify the span.
The API of GT Mondrian is similar to the one from Roassal, but there are a few differences as well. These are described in the Pillar documentation available in the GitHub repo.