The canvas placed nodes with dagre, which orders nodes but knows nothing
about ports: an edge leaves a particular handle and lands on a particular
one, so two producers feeding a consumer in the other order crossed just
before they landed however well the nodes were arranged. The graph was not
a multigraph either, so two messages between one pair of nodes collapsed
into one before crossings were counted, and the endpoint labels were laid
out as 220-wide cards with every handle stacked on a single pixel.
ELK's layered algorithm replaces it. Every declared port is handed to it as
a fixed point on the node's rim, at the fraction `portFraction` puts the
handle at — which the node components now render from the same function —
so what the crossing count is minimised over is what ends up on the screen.
Measured on this installation's flows, with the labels included: `home`
goes from 51 crossings to 6 across and 70 to 29 down, `demo_training` 27 to
5 and 59 to 32, and every graph is the same size or smaller.
The engine answers asynchronously and is a chunk of its own, so positions
became state: the canvas draws nothing until the first layout lands, and an
edit keeps the arrangement it had rather than flashing through the corner.
The entry chunk is untouched and the flow route's own chunk came down 167
to 121 kB, since dagre used to be in it.
Two things the crossings made worse come with it. A hovered edge resolves
to full strength so one line can be followed through a busy rank, and a
feedback edge — one whose target the layout put behind its source — swings
out into a lane beside the graph instead of being drawn through everything
between its ends, which is what "House history" was reported for.
- A node's height follows the ports on its busiest side. It is a function of
the document, so `layoutGraph` reserves exactly what is drawn and nothing
measured is fed back into the layout.
- The three status controls now sit in slots that are there whether the
control is or not. A node running many times a second mounted and unmounted
the stop button on every execution, resizing the card each time.
- A port bound to another flow's message is drawn as a label, naming the node
at the far end and its type. Only the opposite direction was answered
before. The scan behind both is now cached on the store's commit counter
rather than reading every flow per request.
stroblme