bezierFromSweep very slow?

[robx]

A program of mine spends far too much time in bezierFromSweep, through expandTrail':

$ less drawpuzzle.prof 
        Sat Nov  8 11:50 2014 Time and Allocation Profiling Report  (Final)

           drawpuzzle +RTS -p -RTS -s wordsearch-crawlgods.pzl

        total time  =        1.72 secs   (1718 ticks @ 1000 us, 1 processor)
        total alloc = 2,864,711,512 bytes  (excludes profiling overheads)

COST CENTRE     MODULE               %time %alloc

bezierFromSweep Diagrams.TwoD.Arc     85.2   88.2
text'           Diagrams.Puzzles.Lib  11.1   11.4

...

                        expandLine.cap                   Diagrams.TwoD.Offset                1584           0    0.0    0.0    86.8   88.4
                         fromLineCap                     Diagrams.TwoD.Offset                1585           0    0.0    0.0    86.8   88.4
                          transform                      Diagrams.Located                    1595           1    0.0    0.0     0.0    0.0
                           transform                     Diagrams.Trail                      1597           1    0.0    0.0     0.0    0.0
                            onTrail                      Diagrams.Trail                      1598           1    0.0    0.0     0.0    0.0
                          capArc                         Diagrams.TwoD.Offset                1586           1    0.0    0.0    86.8   88.4
                           moveOriginTo                  Diagrams.Located                    1596           1    0.0    0.0     0.0    0.0
                           capArc.fs                     Diagrams.TwoD.Offset                1588           1    0.0    0.0    86.8   88.4
                            arcV                         Diagrams.TwoD.Offset                1591           1    0.0    0.0    86.8   88.4
                             angleBetween                Diagrams.Angle                      1610           1    0.0    0.0     0.0    0.0
                              acosA                      Diagrams.Angle                      1611           1    0.0    0.0     0.0    0.0
                             arc                         Diagrams.TwoD.Arc                   1592           1    0.0    0.0    86.8   88.4
                              arcT                       Diagrams.TwoD.Arc                   1601           1    0.0    0.0    86.8   88.4
                               arcT.bs                   Diagrams.TwoD.Arc                   1607           1    0.1    0.0    86.7   88.3
                                bezierFromSweep          Diagrams.TwoD.Arc                   1608        7565   85.2   88.2    86.7   88.3
                                 renderPuzzle            Main                                1816           0    0.0    0.0     0.0    0.0
                                  renderToFile           Diagrams.Puzzles.CmdLine            1817           0    0.0    0.0     0.0    0.0
                                   renderB               Diagrams.Puzzles.CmdLine            1818           0    0.0    0.0     0.0    0.0

(I have no idea what it means for renderPuzzle to show up in that stack...)

I haven't really managed to figure out what's happening, here. This showed up when porting https://github.com/robx/puzzle-draw to the current development version of diagrams; rendering a certain puzzle now gets "stuck" (keeps allocating and slows down to the point of apparently not making progress). I can't be entirely sure this change is due to the new diagrams version, or because of using diagrams-svg instead of diagrams-cairo for the backend. Or something else.

The relevant function in my code is

drawMarkedWord (MW s e) = lwG onepix . stroke $ expandTrail' with {_expandCap = LineCapRound} 0.4 t
     where t = fromVertices [p2i s, p2i e] # translate (r2 (1/2,1/2))

(p2i makes a point from a pair of Ints).

The input file has 18 such marked words, and is rendered fine with the non-updated version. If I replace LineCapRound by LineCapSquare, it works fine.

[cchalmers]

In ghci:

import Diagrams.Prelude
import Diagrams.TwoD.Offset
expandTrail' (with & expandCap .~ LineCapRound) 0.1 $ (origin ~~ mkP2 1 1.1) -- doesn't hang
expandTrail' (with & expandCap .~ LineCapRound) 0.1 $ (origin ~~ mkP2 1 3) -- hangs

If I had to guess I'd say this is related to #221. Maybe @fryguybob can look into it?

[cchalmers]

Actually it looks like #221 already fixes it. Do you want to try it out @robx?

[fryguybob]

Strange. I'm not sure what the hang would be, but the example @cchalmers gave does not hang for me with the arcCCW branch.

[robx]

Yes, that does appear to fix it. thanks!

[cchalmers]

Great. The branch should be merged soon.