eu.printingin3d.javascad.vrl

Class CSG

java.lang.Object

eu.printingin3d.javascad.vrl.CSG

public class CSG
extends Object

Constructive Solid Geometry (CSG). This implementation is a Java port of https://github.com/evanw/csg.js/ with some additional features like polygon extrude, transformations etc. Thanks to the author for creating the CSG.js library.

Implementation Details All CSG operations are implemented in terms of two functions, Node.clipTo(Node) and Node.invert(), which remove parts of a BSP tree inside another BSP tree and swap solid and empty space, respectively. To find the union of a and b, we want to remove everything in a inside b and everything in b inside a, then combine polygons from a and b into one solid:

     a.clipTo(b);
     b.clipTo(a);
     a.build(b.allPolygons());
 

The only tricky part is handling overlapping coplanar polygons in both trees. The code above keeps both copies, but we need to keep them in one tree and remove them in the other tree. To remove them from b we can clip the inverse of b against a. The code for union now looks like this:

     a.clipTo(b);
     b.clipTo(a);
     b.invert();
     b.clipTo(a);
     b.invert();
     a.build(b.allPolygons());
 

Subtraction and intersection naturally follow from set operations. If union is A | B, differenceion is A - B = ~(~A | B) and intersection is A & B = ~(~A | ~B) where ~ is the complement operator.

Constructor Summary

Constructors

Constructor and Description
CSG(List<Polygon> polygons) Creates a new CSG file based on the given polygons.

Method Summary

Modifier and Type	Method and Description
CSG	difference(CSG csg) Return a new CSG solid representing the difference of this csg and the specified csg.
static CSG	fromPolygons(Polygon... polygons) Constructs a CSG from the specified Polygon instances.
List<Coords3d>	getPoints() Get all the points this CSG holds.
List<Polygon>	getPolygons()
CSG	intersect(CSG csg) Return a new CSG solid representing the intersection of this csg and the specified csg.
List<Facet>	toFacets() Returns with all the facet this CSG object holds.
CSG	transformed(ITransformation transform) Returns a transformed copy of this CSG.
CSG	union(CSG csg) Return a new CSG solid representing the union of this csg and the specified csg.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

CSG

public CSG(List<Polygon> polygons)

Creates a new CSG file based on the given polygons.

Parameters:

polygons - the polygons to be used

Method Detail

fromPolygons

public static CSG fromPolygons(Polygon... polygons)

Constructs a CSG from the specified Polygon instances.

Parameters:

polygons - polygons

Returns:

a CSG instance

getPolygons

public List<Polygon> getPolygons()

Returns:

the polygons of this CSG

getPoints

public List<Coords3d> getPoints()

Get all the points this CSG holds.

Returns:

the points this CSG holds

union

public CSG union(CSG csg)

Return a new CSG solid representing the union of this csg and the specified csg. Note: Neither this csg nor the specified csg are modified.

    A.union(B)

    +-------+            +-------+
    |       |            |       |
    |   A   |            |       |
    |    +--+----+   =   |       +----+
    +----+--+    |       +----+       |
         |   B   |            |       |
         |       |            |       |
         +-------+            +-------+
 

Parameters:

csg - other csg

Returns:

union of this csg and the specified csg

difference

public CSG difference(CSG csg)

Return a new CSG solid representing the difference of this csg and the specified csg. Note: Neither this csg nor the specified csg are modified.

 A.difference(B)

 +-------+            +-------+
 |       |            |       |
 |   A   |            |       |
 |    +--+----+   =   |    +--+
 +----+--+    |       +----+
      |   B   |
      |       |
      +-------+
 

Parameters:

csg - other csg

Returns:

difference of this csg and the specified csg

intersect

public CSG intersect(CSG csg)

Return a new CSG solid representing the intersection of this csg and the specified csg. Note: Neither this csg nor the specified csg are modified.

     A.intersect(B)

     +-------+
     |       |
     |   A   |
     |    +--+----+   =   +--+
     +----+--+    |       +--+
          |   B   |
          |       |
          +-------+
 }
 

Parameters:

csg - other csg

Returns:

intersection of this csg and the specified csg

toFacets

public List<Facet> toFacets()

Returns with all the facet this CSG object holds.

Returns:

all the facet this CSG object holds

transformed

public CSG transformed(ITransformation transform)

Returns a transformed copy of this CSG.

Parameters:

transform - the transform to apply

Returns:

a transformed copy of this CSG