BOSL2/tutorials/Basic_Shapes.md

Basic Shapes Tutorial

Primitives

There are 5 built-in primitive shapes that OpenSCAD provides. square(), circle(), cube(), cylinder(), and sphere(). The BOSL2 library extends or provides alternative to these shapes so that they support more features, and more ways to simply reorient them.

2D Squares

You can still use the built-in square() in the familiar ways that OpenSCAD provides:

    square(100, center=false);

    square(100, center=true);

    square([60,40], center=true);

The BOSL2 library provides an enhanced equivalent to square() called rect(). You can use it in the same way you use square(), but it also provides extended functionality. For example, it allows you to round the corners:

    rect([60,40], center=true, rounding=10);

Or chamfer them:

    rect([60,40], center=true, chamfer=10);

You can even specify which corners get rounded or chamferred. If you pass a list of four size numbers to the rounding= or chamfer= arguments, it will give each corner its own size. In order, it goes from the back-right (quadrant I) corner, counter-clockwise around to the back-left (quadrant II) corner, to the forward-left (quadrant III) corner, to the forward-right (quadrant IV) corner:

    module text3d(text) color("black") text(
        text=text, font="Times", size=10,
        halign="center", valign="center"
    );
    translate([ 50, 50]) text3d("I");
    translate([-50, 50]) text3d("II");
    translate([-50,-50]) text3d("III");
    translate([ 50,-50]) text3d("IV");
    rect([90,80], center=true);

If a size is given as 0, then there is no rounding and/or chamfering for that quadrant's corner:

    rect([60,40], center=true, rounding=[0,5,10,15]);

    rect([60,40], center=true, chamfer=[0,5,10,15]);

You can give both rounding= and chamfer= arguments to mix rounding and chamfering, but only if you specify per corner. If you want a rounding in a corner, specify a 0 chamfer for that corner, and vice versa:

    rect([60,40], center=true, rounding=[5,0,10,0], chamfer=[0,5,0,15]);

Anchors and Spin

Another way that rect() is enhanced over square(), is that you can anchor, spin and attach it.

The anchor= argument is an alternative to center=, which allows more alignment options. It takes a vector as a value, pointing roughly towards the side or corner you want to align to the origin. For example, to align the center of the back edge to the origin, set the anchor to [0,1]:

    rect([60,40], anchor=[0,1]);

To align the front right corner to the origin:

    rect([60,40], anchor=[1,-1]);

To center:

    rect([60,40], anchor=[0,0]);

To make it clearer when giving vectors, there are several standard vector constants defined:

Constant	Direction	Value
LEFT	X-	[-1,0,0]
RIGHT	X+	[1,0,0]
FRONT/FORWARD/FWD	Y-	[0,-1,0]
BACK	Y+	[0,1,0]
BOTTOM/BOT/BTM/DOWN	Z-	[0,0,-1] (3D only.)
TOP/UP	Z+	[0,0,1] (3D only.)
CENTER/CTR	Centered	[0,0,0]

Note that even though these are 3D vectors, you can use most of them, (except UP/DOWN, of course) for anchors in 2D shapes:

    rect([60,40], anchor=BACK);

    rect([60,40], anchor=CENTER);

You can add vectors together to point to corners:

    rect([60,40], anchor=FRONT+RIGHT);

Finally, the spin argument can rotate the shape by a given number of degrees clockwise:

    rect([60,40], anchor=CENTER, spin=30);

Anchoring or centering is performed before the spin:

    rect([60,40], anchor=BACK, spin=30);

2D Circles

The built-in circle() primitive can be used as expected:

    circle(r=50);

    circle(d=100);

    circle(d=100, $fn=8);

The BOSL2 library provides an enhanced equivalent of circle() called oval(). You can use it in the same way you use circle(), but it also provides extended functionality. For example, it allows more control over its size and orientation.

Since a circle in OpenSCAD can only be approximated by a regular polygon with a number of straight sides, this can lead to size and shape inaccuracies. To counter this, the realign= and circum= arguments are also provided.

The realign= argument, if set true, rotates the oval() by half the angle between the sides:

    oval(d=100, $fn=8, realign=true);

The circum= argument, if true, makes it so that the polygon forming the oval() circumscribes the ideal circle instead of inscribing it.

Inscribing the ideal circle:

    difference() {
        circle(d=100, $fn=360);
        oval(d=100, $fn=8);
    }

Circumscribing the ideal circle:

    difference() {
        oval(d=100, $fn=8, circum=true);
        circle(d=100, $fn=360);
    }

Another way that oval() is enhanced over circle(), is that you can anchor, spin and attach it.

    oval(r=50, anchor=BACK);

    oval(r=50, anchor=FRONT+RIGHT);

Using spin on a circle may not make initial sense, until you remember that anchoring is performed before spin:

    oval(r=50, anchor=FRONT, spin=30);

Enhanced 3D Cube

You can use enhanced cube() like the normal OpenSCAD built-in:

    cube(100);

    cube(100, center=true);

    cube([50,40,20], center=true);

You can use anchor similarly to square(), except you can anchor vertically too, in 3D, allowing anchoring to faces, edges, and corners:

    cube([50,40,20], anchor=BOTTOM);

    cube([50,40,20], anchor=TOP+BACK);

    cube([50,40,20], anchor=TOP+FRONT+LEFT);

You can use spin as well, to rotate around the Z axis:

    cube([50,40,20], anchor=FRONT, spin=30);

3D objects also gain the ability to use an extra trick with spin; if you pass a list of [X,Y,Z] rotation angles to spin, it will rotate by the three given axis angles, similar to using rotate():

    cube([50,40,20], anchor=FRONT, spin=[15,0,30]);

3D objects also can be given an orient argument that is given as a vector, pointing towards where the top of the shape should be rotated towards.

    cube([50,40,20], orient=UP+BACK+RIGHT);

If you use anchor, spin, and orient together, the anchor is performed first, then the spin, then the orient:

    cube([50,40,20], anchor=FRONT, spin=45, orient=UP+FWD+RIGHT);

Enhanced 3D Cylinder

You can use the enhanced cylinder() as normal for OpenSCAD:

    cylinder(r=50,h=50);

    cylinder(r=50,h=50,center=true);

    cylinder(d=100,h=50,center=true);

    cylinder(d1=100,d2=80,h=50,center=true);