Spike arrowhead and tail render with oversized joint

[jeffreyrosenbluth]

I believe this bug was introduced with the direction branch.
Sorry for the code length.

{-# LANGUAGE NoMonomorphismRestriction #-}

import Diagrams.Prelude
import Diagrams.Backend.Rasterific.CmdLine
import Data.List.Split (chunksOf)

-- Create a 3 x 3 grid of circles named "1" to "9"
c = circle 1.5 # fc lightgray # lw none # showOrigin
cs = [c # named (show x) | x <- [1..9]]
cGrid = (vcat' $ with & sep .~ 4)
      . map (hcat' $ with & sep .~ 12)
      . chunksOf 3 $ cs

-- For the Shafts.
semicircle = arc xDir (2/5 @@ turn)
quartercircle = arc xDir (1/4 @@ turn)

parab = bezier3 (1 ^& 1) (1 ^& 1) (0 ^& 2)
parab' = reflectX parab

seg = straight unitX
seg' = seg # rotateBy (1/6)

shaft0 = trailFromSegments [parab, seg, parab', seg, parab]
shaft1 = cubicSpline False (trailVertices (shaft0 `at` origin))
shaft2 = cubicSpline False (map p2 [(0,0), (1,0), (0.8, 0.2),(2, 0.2)])

example :: Diagram B R2
example = connect'        arrow1 "1" "2"
        . connect'        arrow2 "4" "3"
        . connect'        arrow3 "1" "6"
        . connectOutside' arrow4 "4" "8"
        . connect'        arrow5 "9" "5"
        . connectOutside' arrow6 "8" "9"
        . connectOutside' arrow7 "8" "7"
        $ cGrid

  where
    -- The arrows
    arrow1 = with & arrowHead .~ dart 
                  & arrowTail .~ quill & shaftStyle %~ lw thick . lc black
                  & arrowShaft .~ shaft0 & headStyle %~ fc blue
                  & tailStyle %~ fc red & tailLength .~ large

    arrow2 = with & arrowHead .~ dart & headLength .~ large
                  & arrowTail .~ dart' & tailLength .~ large
                  & shaftStyle %~ lw thin & arrowShaft .~ shaft1

    arrow3 = with & arrowHead .~ thorn & headLength .~ large
                  & arrowShaft .~ quartercircle & arrowTail .~ noTail
                  & gaps .~ normal

    arrow4 = with & arrowHead .~ dart & arrowTail .~ dart'
                  & arrowShaft .~ shaft2 & headStyle %~ fc teal
                  & tailStyle %~ fc teal & shaftStyle %~ lw thick . lc teal

    arrow5 = with & arrowTail .~ spike' & tailLength .~ large
                  & arrowShaft .~ semicircle & arrowHead .~ spike
                  & headLength .~ large & headStyle %~ fc darkorange
                  & tailStyle %~ fc darkorange
                  & shaftStyle %~ lw veryThick . lc navy

    arrow6 = with & arrowHead .~ tri & arrowTail .~ tri'
                  & headLength .~ large
                  & headStyle %~ fc black . opacity 0.5
                  & tailStyle %~ fc black . opacity 0.5
                  & shaftStyle %~ dashingN [0.01,0.02,0.03,0.01] 0

    arrow7 = arrow6 & arrowHead .~ tri & arrowTail .~ tri'

main = mainWith $ example # frame 0.2

[bergey]

The bug is that the darkorange arrowheads with spike form have the arc part convex instead of concave, right? That does sound like something I would have introduced with Direction. I'll take a look.

[jeffreyrosenbluth]

I believe so, about the concavity. Or it could be something wrong with the joint.

Thanks for looking.

[jeffreyrosenbluth]

There a very small chance that this could be helpful.

[bergey]

@jeffreyrosenbluth The commit I just pushed fixes the obvious rendering error in the arrowhead. Thanks for the very helpful diagram; I was confused about what theta meant.

I don't actually understand how joints work. You mention them upthread; maybe the arc in the joint definition needs to change also. Do you want to take a look, or explain what shape the joint should have in reference to the diagram above?

For this reason I haven't closed the issue yet.

[jeffreyrosenbluth]

@bergey
Thanks for fixing it. Let me try to explain how joints work, although it's hard to fake it so if the example above renders correctly it is unlikely that the spike joint is broken.

In the circle on the right in the above diagram the small piece at 1/2 turn shows how the joint is constructed. Call this piece j, then the joint is reflectX (j === relfectY j).
which is attached to the head so that a shaft of line width w attaches to the head without any gap or the need for overlap.

[bergey]

Thanks for the explanation. That does fit the current definition, so I think this is fixed.