RFR: 8309463: IGV: Dynamic graph layout algorithm

[Roberto Castañeda Lozano]

On Wed, 7 Jun 2023 08:33:12 GMT, emmyyin <duke at openjdk.org> wrote:

> ### Purpose
> 
> IGV currently uses a static layout algorithm to visualize graphs. However, this is problematic due to the use cases of IGV. Most often, the graphs that are visualized are dynamic, meaning the graphs change over time. A dynamic graph can be thought of as a sequence of graphs where a given graph in the sequence is the state of the dynamic graph at that point in time. Static layout algorithms do not account for the rest of the sequence when visualizing a given graph. On one hand, it makes each layout more readable. But on the other hand, the layout for two consecutive graphs in the sequence can be vastly different even though the difference between the graphs is small. This makes it difficult to identify the changes that has occurred to the graph and can damage the internal understanding of the graph that the viewer has obtained. A dynamic layout algorithm takes the changes into account when visualizing a graph. To enhance IGV, such an algorithm has been implemented in this PR.
> 
> The layout drawn by the static layout algorithm is called "sea of nodes", while the layout drawn by the dynamic algorithm is called "stable sea of nodes".
> 
> The difference between the algorithms is illustrated in the following video:
> 
> 
> https://github.com/openjdk/jdk/assets/52547536/35023362-a191-425e-b066-c7474db631f1
> 
> 
> This work is the result of my Master's thesis which can be found [here](https://kth.diva-portal.org/smash/get/diva2:1770643/FULLTEXT01.pdf).
> 
> 
> ### Implementation
> 
> The algorithm is based on update actions that are applied incrementally to a graph layout in order to obtain the layout of the next graph in the sequence. By doing so, the nodes that appears in both graphs remain in their relative positions. A new layout manager called `HierarchicalStableLayoutManager` has been added which holds the core algorithm. The corresponding layout manager with the static layout algorithm is called `HierarchicalLayoutManager`.
> 
> If no layouts have been drawn yet, the `HierarchicalLayoutManager` is used. This is because the dynamic algorithm needs an initial layout to apply the update actions on.
> 
> The whole graph is represented by `LayoutNode` and `LayoutEdge` objects, that holds the positions of the nodes and edges along with other relevant information such as ID, name and size. These are updated, added and removed in accordance with the update actions.
> 
> Since `HierarchicalStableLayoutManager` tries to preserve the node positions, the layouts might get unreadable after a fe...

Thanks Emmy for creating this pull request!
The changes related to improving animations (merged from https://github.com/openjdk/jdk/compare/master...robcasloz:jdk:igv-stable) are orthogonal to the addition of a dynamic layout algorithm and should be extracted, I think, into a separate RFE. That would simplify the task of reviewing and testing your core changes.

> Thanks Emmy for creating this pull request! The changes related to improving animations (merged from [master...robcasloz:jdk:igv-stable](https://github.com/openjdk/jdk/compare/master...robcasloz:jdk:igv-stable)) are orthogonal to the addition of a dynamic layout algorithm and should be extracted, I think, into a separate RFE. That would simplify the task of reviewing and testing your core changes.

@tobiasholenstein has extracted the animation stuff and put your core work in a branch: https://github.com/openjdk/jdk/compare/master...tobiasholenstein:jdk:rebase-toby (thanks @tobiasholenstein!). That branch is probably a better starting point for this PR.

I just tried out the PR a little bit and it is starting to look good and robust, good job Emmy!

Sometimes, the layout in "Stable sea of nodes" changes when going from one graph to the next in the group even though there are no graph changes at all. Is there any simple solution for that? E.g. not re-computing the layout at all if no graph changes are detected.

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PR Comment: https://git.openjdk.org/jdk/pull/14349#issuecomment-1582417671
PR Comment: https://git.openjdk.org/jdk/pull/14349#issuecomment-1586725452
PR Comment: https://git.openjdk.org/jdk/pull/14349#issuecomment-1674363021