Sketches

A Sketch is a planar region: one or more faces on a plane, possibly with holes. Sketches are where most parts begin.

Shapes

Every constructor builds in the world XY plane, centered on the origin:

from smlibpy import *

Rectangle(40, 20)                    # width along X, height along Y
RoundedRectangle(40, 20, 4)          # corner radius 4
Circle(10)
Ellipse(15, 8)
RegularPolygon(10, 6)                # hexagon, corners at radius 10
RegularPolygon(10, 6, inscribed=True)  # hexagon 20 across the flats
Slot(30, 10)                         # 30 long overall, 10 wide
Trapezoid(40, 15, 60)                # base 40, height 15, 60 degree sides
Polygon((0, 0), (30, 0), (30, 10), (10, 25), (0, 25))   # points stay where they are

align moves a sketch relative to the origin: Rectangle(40, 20, align=Align.MIN) puts its lower left corner on the origin.

Combining

plate = RoundedRectangle(60, 40, 6) - Circle(8) - GridLocations(44, 24, 2, 2) * Circle(2.5)
cross = Rectangle(40, 8) + Rectangle(8, 40)
lens = Circle(10).translate(-5, 0) & Circle(10).translate(5, 0)

+ unites, - subtracts, & intersects and ^ keeps what is in exactly one of them. Sketches must lie in the same plane.

From curves

A closed chain of edges becomes a region with make_face. Holes are further closed wires:

outline = Polyline((0, 0), (50, 0), (50, 10), (20, 30), (0, 30), close=True)
bolt_hole = Wire([CenterArc((12, 12), 4, 0, 360)])
bracket = make_face(outline, bolt_hole)

Curves for outlines:

Function	Curve
Line(a, b)	straight segment
Polyline(*points, close=False)	chain of segments (a Wire)
PolarLine(start, length, angle)	segment at an angle
CenterArc(center, radius, start_angle, arc_size)	arc around a center; arc_size=360 is a circle
ThreePointArc(a, through, b)	arc through three points
RadiusArc(a, b, radius)	arc of a radius between two points
SagittaArc(a, b, sagitta)	arc bulging by sagitta
TangentArc(a, b, tangent)	arc leaving a along tangent
EllipticalArc(center, rx, ry, start, end)	ellipse or part of one
Spline(*points, tangents=None, closed=False)	smooth cubic through points
Bezier(*control_points, weights=None)	Bézier curve, rational with weights
FilletPolyline(*points, radius=r)	polyline with rounded corners

Edges chain into wires with Wire([...]) (they are ordered and flipped as needed) or with +. Mirroring half an outline is a common pattern:

half = Wire([
    Line((-25, 0), (-25, -7.5)),
    ThreePointArc((-25, -7.5), (0, -15), (25, -7.5)),
    Line((25, -7.5), (25, 0)),
])
outline = half + half.mirror(Plane.XZ)
body = make_face(outline)

Rounding and offsetting

Rectangle(40, 20).fillet(3)                   # round every corner
Polygon((0, 0), (30, 0), (0, 20)).fillet(2)   # works on any straight-edged outline
Rectangle(40, 20).offset(2)                   # grow; corners become arcs
Rectangle(40, 20).offset(2, round=False)      # grow with sharp corners
(Circle(10) - Circle(5)).offset(-1)           # shrink: the hole grows

Placing a sketch

Sketches move like any shape. Usually they go onto a plane or onto a face of a part:

on_front = Rectangle(20, 10).on(Plane.front)          # stands up in XZ
up_high = Plane.XY.offset(15) * Circle(5)             # Plane * sketch is the same as .on()

part = Box(50, 30, 10)
on_face = Slot(20, 6).on(part.faces().top())          # centered on the top face
off_center = (Pos(10, 5) * Circle(3)).on(part.faces().top())

On a face, the sketch's X axis follows world X where it can; on vertical faces its Y axis points up. face.plane shows the exact frame.

Measuring

s = RoundedRectangle(40, 20, 4) - Circle(5)
s.area                       # exact
s.center()                   # centroid
s.bbox()
len(s.faces()), len(s.faces()[0].inner_wires())

From here, sketches become parts: parts.