Paths, snaps and links

Some things are made of pieces that join end to end (paths, rails, pipes, fences) or have to meet other things at known points (a sign on a wall, a lamp on a post). Snaps say where a piece joins; chain and along= lay pieces out; links tie up loose ends.

snap

snap NAME C DIR [up=DIR] [kind=WORD]

A connection point on a prop: where it is, which way it faces out of the piece, and what kind of thing joins there. DIR is +x -x +y -y +z -z or front back left right up down. Two snaps join when their kinds match (or either is any, the default). Every piece also has snaps from its bounds: base, top, front, back, left, right.

snap start 0,-1,0 -y kind=path
snap end 0,1,0 +y kind=path

chain

chain A B*3 C [at=] [turn=]

Lays pieces end to end, each one's start snap on the last one's end snap (without them, its front on the last one's back). It starts heading +Y. A bend piece turns the rest of the path; a steps piece lifts it.

try it

prop walk_demo "Garden Walk"
  chain path_straight path_bend path_straight path_steps path_straight*2 path_bend_left path_straight

(The path pieces are in the project's paths.parts.)

Along a line of points

LINE ... along="P P P ..." every=D [fit=1] [joints=1] [corners=1] [closed=1] [smooth=N]

Copies down a line of points (x,y or x,y,z), each turned so its +X follows the line:

every=D: one each D metres, centred in its slot;
fit=1: a whole number on each straight, stretched to fill it exactly (a fence panel always meets a post);
joints=1: one where those pieces meet, instead (the posts);
corners=1: one at each point, turned halfway between the straights that meet there;
closed=1: the last point joins the first; smooth=N: along a curve through the points.

The line can be a variable, so one line of points can carry the panels, the posts and the hedge:

try it

prop yard_demo "Fenced Yard"
  set yard="0,0 6,0 6,4 0,4"
  box at=3,2,-.02 size=6.4,4.4,.04 mat=#4a6a2a/plaster
  fence_panel along=yard every=2 fit=1 closed=1 when=i!=1
  fence_post along=yard every=2 fit=1 closed=1 joints=1

link and join

link KIND at=C toward=DIR
join KIND [reach=.6] [radius=.025] [sides=6] [mat=steel_dark] [bulge=] [with=DEF]

A piece can leave loose ends: link marks one, where it is and which way it leaves the piece. A join line bridges the loose ends of its kind that nearly meet: within reach=, facing each other, nearest first, each end once. Ends that already touch count as joined. The bridge is a pipe that leaves one end and curves into the other, so two ends side by side loop round, like a stair rail's return at a half landing. with=DEF draws each bridge with a part of your own instead, laid along +X for length metres. Loose ends come up through use, chain and buildings, so a stair's rails join the next storey's.

try it

def rail_run_demo run=2
  pipe mat=steel_dark radius=.025 0,0,.9 run,0,.9 sides=6
  box at=.1+i*(run-.2)/2,0,on size=.04,.04,.9 mat=steel_dark repeat 3 every 0,0,0
  link rail at=0,0,.9 toward=-x
  link rail at=run,0,.9 toward=+x

prop railing_demo "Railing, Auto Joined"
  rail_run_demo at=0,0,0 run=1.6
  rail_run_demo at=1.9,0,0 run=1.3
  rail_run_demo at=3.4,.2,0 run=1.6 turn=0,0,90
  join rail reach=.6

The three runs come out as one rail, round the corner. With with=:

try it

def swag_demo
  pipe mat=steel_grey radius=.014 0,0,0 length*.5,0,-length*.12 length,0,0 smooth=4 sides=4

prop chain_posts_demo "Posts and Chain"
  bollard at=0,0,0 along="0,0 1.6,.3 3.4,0 5,.8" corners=1
  join chain reach=2.2 with=swag_demo

(bollard is from paths.parts: a post with a link chain on each side.)

Seeing snaps

Built with snaps (project.build(name, snaps=True), which the preview does), a model carries small markers for its snaps, the joints of its chains and its loose ends, each kind its own colour, as a part called snaps. The preview's snap points toggle shows and hides them.