Transforms

mirror(), copy(), and rotate() also have 2D variants that run inside a sketch. They transform the sketch geometry you've drawn — not the finished solid — which means the transformed curves participate in the same face-building step as the rest of the sketch.

2D vs. 3D

The same function names work in both contexts. Called inside sketch(...), they transform sketch geometry. Called outside, they transform solids — see the 3D Transforms guide and Copying guide.

Chained form

Sketch primitives (rect, circle, slot, polygon, bezier, line, …) also expose chainable .translate(), .rotate(), and .mirror() methods — e.g. rect(60, 20).rotate(30) rotates just that rectangle without touching the rest of the sketch. See the Chained Transforms guide for the full reference.

mirror

Mirror sketch geometry across a line or an axis:

import { bezier, extrude, line, mirror, move, sketch } from 'fluidcad/core';

sketch("xy", () => {
    move([0, 0])
    const profile = bezier([0, 0], [60, 0], [40, 80], [120, 100])
    line([120, 0])
    line([0, 0])

    mirror("y", profile)
})

extrude(20)

Signatures inside a sketch:

mirror(line)                            // mirror all sketch geometry across a line
mirror(line, g1, g2, ...)               // mirror specific geometries across a line
mirror("x")                             // mirror across an axis (string or AxisLike)
mirror("y", g1, g2, ...)                // mirror specific geometries across an axis

Any sketched line segment can serve as the mirror line — including construction lines you don't intend to keep in the final face.

copy

Linear copy

Duplicate sketch geometry along one or more axes:

import { circle, copy, extrude, sketch } from 'fluidcad/core';

sketch("xy", () => {
    const c = circle([0, 0], 20)
    copy("linear", "x", { count: 5, offset: 40 }, c)
})

extrude(10)

copy("linear", "x", { count: 4, offset: 40 }, g)          // along X
copy("linear", ["x", "y"], { count: 3, offset: 30 }, g)   // grid along X and Y

Options (same as the 3D form): count, offset, skip.

Circular copy

Duplicate sketch geometry around a 2D center point (not an axis — that's the 3D form):

import { circle, copy, extrude, sketch } from 'fluidcad/core';

sketch("xy", () => {
    const c = circle([80, 0], 15)
    copy("circular", [0, 0], { count: 8, angle: 360 }, c)
})

extrude(10)

copy("circular", [0, 0], { count: 8, angle: 360 }, g)

Options: count, angle, skip.

rotate

Rotate sketch geometry around the sketch origin:

sketch("xy", () => {
    const r = rect(60, 20)
    rotate(30, true, r)        // rotate a copy by 30°, keep the original
})

The 2D form takes an angle only — it always rotates around the sketch's local Z axis (the plane normal). To rotate a copy instead of moving the original, pass true as the second argument.

When sketch axes don't match world axes

Bare axis strings like "x" and "y" always refer to world axes. On the XY plane that matches the sketch's own axes, but on other planes it doesn't:

// ❌ fails: world Y is the front plane's normal — the mirror plane collapses
sketch("front", () => {
    const b = bezier([200, 200], [-120, 380], [200, 450], [0, 600])
    mirror("y", b)
})

Use local() to resolve an axis string against the active sketch's local coordinate system instead:

import { bezier, extrude, local, mirror, sketch } from 'fluidcad/core';

sketch("front", () => {
    const b = bezier([200, 200], [-120, 380], [200, 450], [0, 600])
    mirror(local("y"), b)
})

extrude(20)

local("y") on sketch("front") resolves to world +Z (the sketch's vertical), so the mirror works as expected.

Sketch plane	local("x")	local("y")
"xy" / "top"	world +X	world +Y
"xz" / "front"	world +X	world +Z
"yz" / "right"	world +Y	world +Z

local() also works with face-based sketches and custom plane() objects.

Mixing with bare strings

local() is opt-in per argument — bare strings stay world-relative:

sketch("front", () => {
    // local("y") → sketch-local Y (world Z); "x" → world X (also the
    // sketch's local X on "front").
    copy("linear", [local("y"), "x"], { count: 2, offset: 30 }, shape)
})

When you don't need it

• rotate(angle) inside a sketch already rotates around the sketch's local Z — no axis argument, no local() needed.
• On sketch("xy"), the world and local axes match, so bare strings work.
• When you pass a sketched line (e.g. a construction line) to mirror(), the geometry already lives on the sketch plane.