Getting started with rpic

A first picture

Primitives placed in sequence flow in the current direction (right, by default); arrow connects them; arc bends between named positions:

library(rpic)

svg <- rpic_svg('
boxht = 0.35; boxwid = 0.8
A: box "input"
arrow
box "process" fill 0.9
arrow
E: ellipse "output"
arc cw -> from A.n to E.n
')

input, process and output connected by arrows, with an arc looping over the top

Positioning

Objects can be labelled (A:), addressed by compass corners (.n, .e, .c, …) or by ordinals (last circle, 2nd box), and placed with expressions — including fractions of the way between two points:

rpic_svg('
A: box "A" wid 0.6 ht 0.4
B: box "B" wid 0.6 ht 0.4 at A + (1.6, 0)
line dashed from A.e to B.w
circle rad 0.06 fill 0 at 1/2 between A.e and B.w
"midpoint" at last circle.s below
arrow from A.n up 0.3 then right 1.6 then down 0.3 to B.n
"the long way" at 1/2 between A.n and B.n + (0, 0.42)
')

two boxes joined by a dashed line with a marked midpoint, and an arrow taking the long way over the top

Programmability

pic is a little language: for/if, variables, define macros with $1…$9, and sprintf are all built in:

rpic_svg('
for i = 0 to 5 do {
  circle rad 0.12 fill i/6 at (i * 0.4, 0)
}
')

six circles in a row, shading from black to light gray

TeX math labels

With texlabels = TRUE (or texlabels = 1 in the source), a label written entirely as $…$ is typeset as TeX math, natively — KaTeX-grade quality with exact metrics, so boxes fit around formulas correctly. Write TeX commands with a single backslash in the pic source (escaped as \\ inside an R string):

rpic_svg('
box "$\\frac{1}{2\\pi}\\int_{-\\infty}^{\\infty} f(t)\\,e^{-i\\omega t}\\,dt$" fit
', texlabels = TRUE)

a box fitted around the Fourier-transform integral, typeset as math

rpic extensions

Beyond classic pic, opt-in extensions cover linear gradient fills, hatch patterns, curly brace annotations, margin, fit, opacity, layers (behind) and more — each documented with live examples at rpic.dev. They are inert for classic input:

rpic_svg('
B: box wid 0.9 ht 0.55 gradient "steelblue" "white"
"gradient" at B.c
C: circle rad 0.3 hatch hatchangle 45 at B.e + (1.0, 0)
"hatch" at C.s below
brace from B.nw + (0, 0.15) to C.ne + (0, 0.15) up "extensions"
')

a gradient-filled box and a hatched circle spanned by a curly brace labelled extensions

Errors you can point at

Compile failures raise a classed rpic_error condition whose info field carries the structured diagnostic — position (always relative to your source), kind, and a did-you-mean hint:

tryCatch(
  rpic_svg("bxo", circuits = TRUE),
  rpic_error = function(e) list(line = e$info$line, hint = e$info$hint)
)
#> $line
#> [1] 1
#> $hint
#> [1] "did you mean `box`?"

Where next

• vignette("circuits") — the native circuit-element library;
• vignette("class-and-animate") — CSS class hooks and the animation manifest;
• rpic_register_knitr() — write pic directly in R Markdown / Quarto chunks;
• rpic.dev — the full language documentation.