revisit WebGL with d3 force layout

[smurp]

There is now some example code for rendering force layouts on the GPU. This is not a drop-in replacement for everything needed by current HuViz, but it gives hints on how to implement what we would need.

https://bl.ocks.org/vicapow/7f14a531dec565ca0884

There are many things which would have to be implemented in conjunction with GL shaders to achieve a transition to rendering HuViz on WebGL.

• [ ] creating the edge handles, the virtual nodes used for focused edge detection
• [ ] discovering the focused node and focused edge driven by mouse position
• [ ] communicating the labelling data into the visualization
• [ ] calculating edge sway (ie curvature)
• [ ] possibly rendering the speech-bubble-pointer in WebGL
• [ ] possible cross-browser issues...
• [ ] node dragging interaction

[ilyadorosh]

https://bugs.chromium.org/p/chromium/issues/detail?id=688243

[smurp]

I initially thought this would be incompatible with boxNG but given that boxNG is still drawing the nodes as wee circles (using CANVAS) the drawing of edges and circular node could, in fact, be done with the GPU. The complexity with a mixture of GPU graph layout and labels in DIVs (ala boxNG) would be with the exfiltration of position data out to the DOM layer. A solution would be needed for this. Presumably a trick would be possible such as an offscreen area where location data were exfiltrated as a packed integer array (in visible node order) encoded as hues.