Objects

Objects are the building blocks of your scene. There are a lot of different types of objects supported by POV-Ray. In the following sections, we describe Finite Solid Primitives, Finite Patch Primitives and Infinite Solid Primitives. These primitive shapes may be combined into complex shapes using Constructive Solid Geometry (also known as CSG).

The basic syntax of an object is a keyword describing its type, some floats, vectors or other parameters which further define its location and/or shape and some optional object modifiers such as texture, interior_texture, pigment, normal, finish, interior, bounding, clipping or transformations. Specifically the syntax is:

OBJECT:
  FINITE_SOLID_OBJECT | FINITE_PATCH_OBJECT | 
  INFINITE_SOLID_OBJECT | CSG_OBJECT | LIGHT_SOURCE |
  object { OBJECT_IDENTIFIER [OBJECT_MODIFIERS...] }
FINITE_SOLID_OBJECT:
  BLOB | BOX | CONE | CYLINDER | HEIGHT_FIELD | ISOSURFACE | JULIA_FRACTAL |
  LATHE | OVUS | PARAMETRIC | PRISM | SPHERE | SPHERE_SWEEP | SUPERELLIPSOID |
  SOR | TEXT | TORUS
FINITE_PATCH_OBJECT:
  BICUBIC_PATCH | DISC | MESH | MESH2 | POLYGON | TRIANGLE |
  SMOOTH_TRIANGLE
  INFINITE_SOLID_OBJECT:
  PLANE | POLY | CUBIC | QUARTIC | QUADRIC 
CSG_OBJECT:
  UNION | INTERSECTION | DIFFERENCE | MERGE

Object identifiers may be declared to make scene files more readable and to parameterize scenes so that changing a single declaration changes many values. An identifier is declared as follows.

OBJECT_DECLARATION:
  #declare IDENTIFIER = OBJECT |
  #local IDENTIFIER = OBJECT

Where IDENTIFIER is the name of the identifier up to 40 characters long and OBJECT is any valid object. To invoke an object identifier, you wrap it in an object{...} statement. You use the object statement regardless of what type of object it originally was. Although early versions of POV-Ray required this object wrapper all of the time, now it is only used with OBJECT_IDENTIFIERS.

Object modifiers are covered in detail later. However here is a brief overview.

The texture describes the surface properties of the object. Complete details are in textures. Textures are combinations of pigments, normals, and finishes. In the section pigment you will learn how to specify the color or pattern of colors inherent in the material. In normal, we describe a method of simulating various patterns of bumps, dents, ripples or waves by modifying the surface normal vector. The section on finish describes the reflective properties of the surface. The Interior is a feature introduced in POV-Ray 3.1. It contains information about the interior of the object which was formerly contained in the finish and halo parts of a texture. Interior items are no longer part of the texture. Instead, they attach directly to the objects. The halo feature has been discontinued and replaced with a new feature called Media which replaces both halo and atmosphere.

Bounding shapes are finite, invisible shapes which wrap around complex, slow rendering shapes in order to speed up rendering time. Clipping shapes are used to cut away parts of shapes to expose a hollow interior. Transformations tell the ray-tracer how to move, size or rotate the shape and/or the texture in the scene.

Finite Solid Primitives

There are seventeen different solid finite primitive shapes: blob, box, cone, cylinder, height field, isosurface, Julia fractal, lathe, ovus, parametric, prism, sphere, sphere_sweep, superellipsoid, surface of revolution, text and torus. These have a well-defined inside and can be used in CSG (see Constructive Solid Geometry). They are finite and respond to automatic bounding. You may specify an interior for these objects.

Finite Patch Primitives

There are six totally thin, finite objects which have no well-defined inside. They are bicubic patch, disc, smooth triangle, triangle, polygon, mesh, and mesh2. They may be combined in CSG union, but cannot be used inside a clipped_by statement.

Note: Patch objects may give unexpected results when used in differences and intersections.

These conditions apply:

1. Solids may be differenced from bicubic patches with the expected results.
2. Differencing a bicubic patch from a solid may give unexpected results.
• Especially if the inverse keyword is used!
3. Intersecting a solid and a bicubic patch will give the expected results.
• The parts of the patch that intersect the solid object will be visible.
4. Merging a solid and a bicubic patch will remove the parts of the bicubic patch that intersect the solid.

Because these types are finite POV-Ray can use automatic bounding on them to speed up rendering time. As with all shapes they can be translated, rotated and scaled.

Infinite Solid Primitives

There are six polynomial primitive shapes that are possibly infinite and do not respond to automatic bounding. They are plane, cubic, poly, quartic, polynomial, and quadric. They do have a well defined inside and may be used in CSG and inside a clipped_by statement. As with all shapes they can be translated, rotated and scaled.

Constructive Solid Geometry

In addition to all of the primitive shapes POV-Ray supports, you can also combine multiple simple shapes into complex shapes using Constructive Solid Geometry (CSG). There are four basic types of CSG operations: union, intersection, difference, and merge. CSG objects can be composed of primitives or other CSG objects to create more, and more complex shapes.

Inside and Outside

Most shape primitives, like spheres, boxes and blobs divide the world into two regions. One region is inside the object and one is outside. Given any point in space you can say it is either inside or outside any particular primitive object. Well, it could be exactly on the surface but this case is rather hard to determine due to numerical problems.

Even planes have an inside and an outside. By definition, the surface normal of the plane points towards the outside of the plane. You should note that triangles cannot be used as solid objects in CSG since they have no well defined inside and outside. Triangle-based shapes (mesh and mesh2) can only be used in CSG when they are closed objects and have an inside vector specified.

Note: Although the triangle, the bicubic_patch and some other shapes have no well defined inside and outside, they have a front- and backside which makes it possible to use a texture on the front side and an interior_texture on the back side.

CSG uses the concepts of inside and outside to combine shapes together as explained in the following sections.

Imagine you have two objects that partially overlap like shown in the figure below. Four different areas of points can be distinguished: points that are neither in object A nor in object B, points that are in object A but not in object B, points that are not in object A but in object B and last not least points that are in object A and object B.

Two overlapping objects.

Keeping this in mind it will be quite easy to understand how the CSG operations work.

When using CSG it is often useful to invert an object so that it will be inside-out. The appearance of the object is not changed, just the way that POV-Ray perceives it. When the inverse keyword is used the inside of the shape is flipped to become the outside and vice versa.

The inside/outside distinction is not important for a union, but is important for intersection, difference, and merge. Therefore any objects may be combined using union but only solid objects, i.e. objects that have a well-defined interior can be used in the other kinds of CSG. The objects described in Finite Patch Primitives have no well defined inside/outside. All objects described in the sections Finite Solid Primitives and Infinite Solid Primitives.

Object Modifiers

A variety of modifiers may be attached to objects. The following items may be applied to any object:

OBJECT_MODIFIER:
  clipped_by { UNTEXTURED_SOLID_OBJECT... } |
  clipped_by { bounded_by }                 |
  bounded_by { UNTEXTURED_SOLID_OBJECT... } |
  bounded_by { clipped_by }                 |
  no_shadow                  |
  no_image [ Bool ]          |
  no_radiosity [ Bool ]      |
  no_reflection [ Bool ]     |
  inverse                    |
  sturm [ Bool ]             |
  hierarchy [ Bool ]         |
  double_illuminate [ Bool ] |
  hollow  [ Bool ]           |
  interior { INTERIOR_ITEMS... }                        |
  material { [MATERIAL_IDENTIFIER][MATERIAL_ITEMS...] } |
  texture { TEXTURE_BODY }   |
  interior_texture { TEXTURE_BODY } |
  pigment { PIGMENT_BODY }   |
  normal { NORMAL_BODY }     |
  finish { FINISH_ITEMS... } |
  photons { PHOTON_ITEMS...}
  radiosity { RADIOSITY_ITEMS...}
  TRANSFORMATION

Transformations such as translate, rotate and scale have already been discussed. The modifiers Textures and its parts Pigment, Normal, and Finish as well as Interior, and Media (which is part of interior) are each in major chapters of their own below. In the sub-sections below we cover several other important modifiers: clipped_by, bounded_by, material, inverse, hollow, no_shadow, no_image, no_reflection, double_illuminate, no_radiosity and sturm. Although the examples below use object statements and object identifiers, these modifiers may be used on any type of object such as sphere, box etc.