Labels & ordinals

pic gives you two ways to refer back to something you drew: give it a name, or point at it by order.

Labels

A capitalized name followed by a colon labels the next object (or a bare position). Labels are how larger pictures stay readable.

.PS
In:  circle "in" rad 0.22
Sum: circle rad 0.1 at In + (0.9, 0)
Out: box "out" wid 0.6 ht 0.45 at Sum + (1.0, 0)
arrow from In.e to Sum.w
arrow from Sum.e to Out.w
line -> from Out.s down 0.35 then left Out.x - Sum.x then to Sum.s
.PE

A label can also name a plain point (P: (0.9, -0.5)) — handy for wiring.

Ordinals

last, 2nd, 3rd last … select objects by their order of appearance, optionally filtered by kind:

.PS
box "1"; move; box "2"; move; circle "c" rad 0.3
arrow from last box.s down 0.3
arrow from 1st box.s down 0.3
line dashed from last circle.n up 0.25
.PE

last on its own matches the most recent object of any kind; last box filters by kind. This is exactly dpic’s behavior.

Here

Here (capitalized, as in classic pic) is the current position. The classic use: stash a junction point while walking a wire, then branch from it later —

.PS
box "in" wid 0.55 ht 0.4
line right 0.4
H: Here                # stash the junction
arrow right 0.4
box "out" wid 0.55 ht 0.4
dot at H
line -> from H down 0.5 then right 0.4
box "log" wid 0.55 ht 0.4
.PE

The dot marks exactly the point H remembered.

Anchors on references

Every reference — label or ordinal — exposes the same compass anchors:

.PS
A: box "A"
box "B" with .w at A.e + (0.5, 0)
line dotted from A.ne to last box.nw
line dotted from A.se to last box.sw
.PE

Where to go next

• Variables & macros — parameterize with define, loop with for