Adaptive arrowheads

[maxitg]

Changes

• Closes Adaptive arrowhead size #217.
• Make the arrowheads adaptively change from 0.1 to 0.185 depending on the size of the graph.
• The style spec is contributed by Jeremy Davis.

Comments

• The arrowhead function is now in style.m. This is the first precedent where a function is used for a style.

Tests

• Comparison of old arrowheads (on the left), and the new adaptive ones (on the right):

In[] := Grid@Transpose[
  WolframModel[{{1, 2, 3}, {4, 5, 6}, {1, 4}} -> {{2, 7, 8}, {3, 9, 
         10}, {5, 11, 12}, {6, 13, 14}, {8, 12}, {11, 10}, {13, 
         7}, {14, 9}}, {{1, 1, 1}, {1, 1, 1}, {1, 1}, {1, 1}, {1, 1}},
       3]["EventsStatesPlotsList", "ArrowheadLength" -> #] & /@ {0.1, 
    Automatic}]

• The new spec makes it possible to see arrows on graphs 1.85 larger than before:

In[] := WolframModel[{{1, 2}, {2, 3}} -> {{4, 2}, {4, 1}, {2, 1}, {3, 
    4}}, {{1, 2}, {2, 3}, {3, 4}, {4, 1}}, 5, "FinalStatePlot"]

• The new spec function can be looked up with WolframPhysicsProjectStyleData:

In[] := WolframPhysicsProjectStyleData["SpatialGraph", 
  "ArrowheadLengthFunction"]
Out[] = Max[0.1, Min[0.185, 0.066 + 0.017 #PlotRange]] &

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This change is 

[GetJonWithIt]

Appears to match the style spec from Jeremy, and no longer produces weird arrow sizes in corner cases. Approved to merge.