# OpenSCAD User Manual/CSG Modelling

### boolean overviewEdit

##### 2D examplesEdit

```
union() {square(10);circle(10);} // square or circle
difference() {square(10);circle(10);} // square and not circle
difference() {circle(10);square(10);} // circle and not square
intersection(){square(10);circle(10);} // square and circle
```

##### 3D examplesEdit

```
union() {cube(12, center=true); sphere(8);} // cube or sphere
difference() {cube(12, center=true); sphere(8);} // cube and not sphere
difference() {sphere(8); cube(12, center=true);} // sphere and not cube
intersection(){cube(12, center=true); sphere(8);} // cube and sphere
```

### unionEdit

Creates a union of all its child nodes. This is the **sum** of all children (logical **or**).

May be used with either 2D or 3D objects, but don't mix them.

```
//Usage example:
union() {
cylinder (h = 4, r=1, center = true, $fn=100);
rotate ([90,0,0]) cylinder (h = 4, r=0.9, center = true, $fn=100);
}
```

Remark: union is implicit when not used. But it is mandatory, for example, in difference to group first child nodes into one.

### differenceEdit

Subtracts the 2nd (and all further) child nodes from the first one (logical **and not**).

May be used with either 2D or 3D objects, but don't mix them.

```
Usage example:
difference() {
cylinder (h = 4, r=1, center = true, $fn=100);
rotate ([90,0,0]) cylinder (h = 4, r=0.9, center = true, $fn=100);
}
```

##### difference with multiple childrenEdit

Note, in the second instance, the result of adding a union of the 1st and 2nd children.

```
// Usage example for difference of multiple children:
$fn=90;
difference(){
cylinder(r=5,h=20,center=true);
rotate([00,140,-45]) color("LightBlue") cylinder(r=2,h=25,center=true);
rotate([00,40,-50]) cylinder(r=2,h=30,center=true);
translate([0,0,-10])rotate([00,40,-50]) cylinder(r=1.4,h=30,center=true);
}
// second instance with added union
translate([10,10,0]){
difference(){
union(){ // combine 1st and 2nd children
cylinder(r=5,h=20,center=true);
rotate([00,140,-45]) color("LightBlue") cylinder(r=2,h=25,center=true);
}
rotate([00,40,-50]) cylinder(r=2,h=30,center=true);
translate([0,0,-10])rotate([00,40,-50]) cylinder(r=1.4,h=30,center=true);
}
}
```

### intersectionEdit

Creates the intersection of all child nodes. This keeps the **overlapping** portion (logical **and**).

Only the area which is common or shared by **all** children is retained.

May be used with either 2D or 3D objects, but don't mix them.

```
//Usage example:
intersection() {
cylinder (h = 4, r=1, center = true, $fn=100);
rotate ([90,0,0]) cylinder (h = 4, r=0.9, center = true, $fn=100);
}
```

### renderEdit

**Warning:** Using render, always calculates the CSG model for this tree (even in OpenCSG preview mode).
This can make previewing very slow and OpenSCAD to appear to hang/freeze.

```
Usage example:
render(convexity = 1) { ... }
```

convexity | Integer. The convexity parameter specifies the maximum number of front and back sides a ray intersecting the object might penetrate. This parameter is only needed for correctly displaying the object in OpenCSG preview mode and has no effect on the polyhedron rendering. |

This image shows a 2D shape with a convexity of 4, as the ray indicated in red crosses the 2D shape a maximum of 4 times. The convexity of a 3D shape would be determined in a similar way. Setting it to 10 should work fine for most cases.