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4.2.9 INST Files

The conventional suffix for a INST file is .inst.

There is no INST BINARY format.

An INST applies a 4x4 (or (N+1)x(N+1) in the context of ND-viewing) transformation to another OOGL object. It begins with INST followed by these sections which may appear in any order:

     geom oogl-object

specifies the OOGL object to be instantiated. See References, for the syntax of an oogl-object. The keyword unit is a synonym for geom.

     transform   ["{"] 4x4 transform ["}"]

specifies a single transformation matrix. Either the matrix may appear literally as 16 numbers, or there may be a reference to a "transform" object, i.e.

         "<" file-containing-4x4-matrix


         ":" symbol-representing-transform-object

Another way to specify the transformation is


The oogl-object must be a TLIST object (list of transformations) object, or a LIST whose members are ultimately TLIST objects. In effect, the transforms keyword takes a collection of 4x4 matrices and replicates the geom object, making one copy for each 4x4 matrix.

If no transform nor transforms keyword appears, no transformation is applied (actually the identity is applied). You could use this for, e.g., wrapping an appearance around an externally-supplied object, though a single-membered LIST would do this more efficiently.

See Transformation matrices, for the matrix format.

When replicating a single geometry by means of a TLIST object (see `transforms' above) it may be useful to transform texture co-ordinates by another list of transformations; that list can be specified by


The number of texture transformations must match the number of geometry transformations. The SPHERE object (see Sphere Objects) uses this technique to generate an entire textured sphere out of some fraction of a sphere (usually one octant).

A single (N+1)-dimensional transformation can be specified by

     ntransform ["{"] N+1 N+1 (N+1)x(N+1) floats ["}"]

This gives a single N+1-dimensional transformation matrix. Either the matrix may appear literally as (N+1)x(N+1) numbers, or there may be a reference to an `ntransform' object, i.e.

         "<" file-containing-(N+1)x(N+1)-matrix


         ":" symbol-representing-ntransform-object

See ND Transformation matrices, for the matrix format.

Two more INST fields are accepted: location and origin.

Note that location as well as origin are ignored if this INST object carries an ntransform. Also, if ND-viewing is active (ND-axes command, see GCL) then INST objects with origin unequal to local will not be drawn, though the location stuff may work (or not).

     location [global or camera or ndc or screen or local]

Normally an INST specifies a position relative to its parent object; the location field allows putting an object elsewhere.

location local is the default; the object is positioned relative to its parent.

     origin [global or camera or ndc or screen or local] x y z

The origin field translates the contents of the INST to place the origin at the specified point of the given coordinate system. Unlike location, it doesn't change the orientation, only the choice of origin. Both location and origin can be used together.

So for example

     { INST
       location screen
       origin ndc 0 0 -.99
       geom { < xyz.vect }
       transform { 100 0 0 0  0 100 0 0  0 0 -.009 0   0 0 0 1 }

places xyz.vect's origin in the center of the window, just beyond the near clipping plane. The unit-length X and Y edges are scaled to be just 100 screen units – pixels – long, regardless of the size of the window.