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Shape Attributes

Properties

The 'property' property of a solid can be used to store metadata for the object, for example the coordinate of a specific point of interest of the solid. Whenever the object is transformed (i.e. rotated, scaled or translated), the properties are transformed with it. So the property will keep pointing to the same point of interest even after several transformations have been applied to the solid.

Properties can have any type, but only the properties of classes supporting a 'transform' method will actually be transformed. This includes CSG.Vector3D, CSG.Plane and CSG.Connector. In particular CSG.Connector properties (see below) can be very useful: these can be used to attach a solid to another solid at a predetermined location regardless of the current orientation.

It's even possible to include a CSG solid as a property of another solid. This could be used for example to define the cutout cylinders to create matching screw holes for an object. Those 'solid properties' get the same transformations as the owning solid but they will not be visible in the result of CSG operations such as union().

Other kind of properties (for example, strings) will still be included in the properties of the transformed solid, but the properties will not get any transformation when the owning solid is transformed.

All primitive solids have some predefined properties, such as the center point of a sphere (TODO: document).

The solid resulting from CSG operations (union(), subtract(), intersect()) will get the merged properties of both source solids. If identically named properties exist, only one of them will be kept.

var cube = CSG.cube({radius: 1.0});
cube.properties.aCorner = new CSG.Vector3D([1, 1, 1]);
cube = cube.translate([5, 0, 0]);
cube = cube.scale(2);
// cube.properties.aCorner will now point to [12, 2, 2],
// which is still the same corner point 
 
// Properties can be stored in arrays; all properties in the array
// will be transformed if the solid is transformed:
cube.properties.otherCorners = [
  new CSG.Vector3D([-1, 1, 1]),
  new CSG.Vector3D([-1, -1, 1])
];
 
// and we can create sub-property objects; these must be of the 
// CSG.Properties class. All sub properties will be transformed with
// the solid:
cube.properties.myProperties = new CSG.Properties();
cube.properties.myProperties.someProperty = new CSG.Vector3D([-1, -1, -1]);

Measurements

Bounds

The getBounds() function can be used to retrieve the bounding box of an object, returning an array with two points specifying the minimum and maximum coordinates, i.e. X, Y, Z values.

Connectors

The CSG.Connector class is intended to facilitate attaching two solids to each other at a predetermined location and orientation. For example suppose we have a CSG solid depicting a servo motor and a solid of a servo arm: by defining a Connector property for each of them, we can easily attach the servo arm to the servo motor at the correct position (i.e. the motor shaft) and orientation (i.e. arm perpendicular to the shaft) even if we don't know their current position and orientation in 3D space.

In other words Connector give us the freedom to rotate and translate objects at will without the need to keep track of their positions and boundaries. And if a third party library exposes connectors for its solids, the user of the library does not have to know the actual dimensions or shapes, only the names of the connector properties.

A CSG.Connector consist of 3 properties:

  • point: a CSG.Vector3D defining the connection point in 3D space
  • axis: a CSG.Vector3D defining the direction vector of the connection (in the case of the servo motor example it would point in the direction of the shaft)
  • normal: a CSG.Vector3D direction vector somewhat perpendicular to axis; this defines the “12 o'clock” orientation of the connection.

When connecting two connectors, the solid is transformed such that the <b>point</b> properties will be identical, the <b>axis</b> properties will have the same direction (or opposite direction if mirror == true), and the <b>normal</b>s match as much as possible.

Connectors can be connected by means of two methods: A CSG solid's connectTo() function transforms a solid such that two connectors become connected. Alternatively we can use a connector's getTransformationTo() method to obtain a transformation matrix which would connect the connectors. This can be used if we need to apply the same transform to multiple solids.

var cube1 = CSG.cube({radius: 10});
var cube2 = CSG.cube({radius: 4});
 
// define a connector on the center of one face of cube1
// The connector's axis points outwards and its normal points
// towards the positive z axis:
cube1.properties.myConnector = new CSG.Connector([10, 0, 0], [1, 0, 0], [0, 0, 1]);
 
// define a similar connector for cube 2:
cube2.properties.myConnector = new CSG.Connector([0, -4, 0], [0, -1, 0], [0, 0, 1]);
 
// do some random transformations on cube 1:
cube1 = cube1.rotateX(30);
cube1 = cube1.translate([3.1, 2, 0]);
 
// Now attach cube2 to cube 1:
cube2 = cube2.connectTo(
  cube2.properties.myConnector, 
  cube1.properties.myConnector, 
  true,   // mirror 
  0       // normalrotation
);
 
// Or alternatively:
var matrix = cube2.properties.myConnector.getTransformationTo(
  cube1.properties.myConnector, 
  true,   // mirror 
  0       // normalrotation
);
cube2 = cube2.transform(matrix);
 
var result = cube2.union(cube1);