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Houdini Development Toolkit - Version 6.5

Side Effects Software Inc. 2004

Objects

Transforming an Object

When an object cooks, it pre-computes the values of the values of various transformation matrices for later retrieval. These matrices are:

If you wish to alter the computation of objects, you must create a new object type that overrides the cookMe method of its baseclass object (see the file $H/toolkit/samples/OBJ/OBJ_Shake.C for an example of a custom geometry object that adds its own customizations to the computation of the transform). In your cookMe method you must set the contents of all three matrices listed above.

By default, objects compute their local transform as follows:

  1. Compute the basic transform.
    This is achieved by passing the appropriate parameters down to OP_Node::buildXform. In other words, this is the standard transform built as you'll find in most graphics books. It combines the object's translate, rotate, scale, and pivot channels into a matrix, taking into account the transform and rotate orders for that object.
  2. Add on transformations due to the path object.
    If a path object has been specified, then the transformation that would position and orient the object onto the path are appended to the transformation computed before. (ie the changes are cumulative) The actual computations are too complicated to describe.
  3. Add on rotations due to the lookat object.
    If a look at object is specified, then the object is also rotated so that its negative z-axis is pointing at the specified object.

The object's global transform is computed by simply combining its local transform with the global transform of its parent (if any). And, of course, the inverse of its global transform is the result of inverting the global transform matrix.


Table of Contents
Operators | Surface Operations | Particle Operations | Composite Operators | Channel Operators
Material & Texture | Objects | Command and Expression | Render Output |
Mantra Shaders | Utility Classes | Geometry Library | Image Library | Clip Library
Customizing UI | Questions & Answers

Copyright © 2004 Side Effects Software Inc.
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