Paste

可以让你在基础的NURBS几何体上粘贴局部的精细效果。

Introduction

The Paste op is a local refinement tool that doesn’t increase the complexity of the base surface, yet allows detail to move freely on the base surface.

A feature of the Paste op is that regardless of the pasting method, the base hierarchy will always keep its primitive numbers. The features will be added to the existing model, so their numbers will always be higher than those of the base(s). This allows you to change the resolution of the animation at the base level and animate base points at various resolutions without worrying about point-number changes.

Two Ways of Building a Paste Hierarchy

There are two ways of building a paste hierarchy; from outside the base surface, and from inside the base surface.

Adding Detail from Outside

This is done using the Paste op, with two inputs: the feature and the base.

Parametric Paste

Along Vector (Projective) Paste

1. In a Parametric Paste, the Paste op places the feature on an area of the base surface delimited by four user-defined isoparametric curves. The feature is thus aligned with the base surface isoparametrically.

The advantage of Parametric Pasting is that the feature is guaranteed to “land” on the base within a well determined parametric area regardless of the base’s shape, position and orientation; also, the continuity between feature and base is enhanced by the parametric alignment between the two surfaces.

2. In a Projective Paste, the four corners of the feature surface are projected onto the base surface first. Then the entire feature is moulded onto the base such that its corners match the four projected points. The feature is not aligned with the base isoparametrically.

The advantage of the Projective Paste is that it applies the feature onto the base intuitively along a vector, without any parametric alignment, generally producing a mould that is similar in shape and orientation to the original (unpasted feature).

Growing Detail from Within

If you use only one input to the Paste op, you can still create a pasted surface using a method called “spawning”. This technique extracts a portion of the base surface and turns it into a pasted surface that shares the base’s shape and underlying domain in that area (much like an onion peel).

The new surface can be further refined and modeled to generate the desired detail; it can be spawned recursively to add even more detail. This new surface may be lofted above the base surface by the amount specified by the Height parameter. This is an easy way to build offset surfaces. The advantage of the spawning technique is that it guarantees perfect geometric and texture continuity between feature and base.

Some Notes on Getting Good Pasted Surfaces

The flatter the base surface, the less distorted the pasted surface will be.

The more tentacles on the feature surface (i.e. the more refined the feature), the better its moulding on the base surface.

The more vertical the initial tentacles, the more closely the pasted surface will follow the features of the base.

The shorter the tentacle, the closer to the base surface it will be. Therefore, in general it is better to start with a flat base surface, and deform it in the middle, leaving the edges so their slope is flat. This yields better boundary continuity across feature and surface.

It is also good to ensure that the feature starts out as a rectangular grid and all the interior deformations don’t “spill-out” of the rectangular area.

Tip

If the feature doesn’t have enough resolution (i.e. tentacles), you may have a problem with boundary continuity, in which case you can add a Refine SOP to the feature before doing the paste, or increase the number of boundary isoparms with the Belt parameters.

Surface Deletion

You can delete surfaces with Delete SOP and Unpaste SOP, as well as in the view.

Current Limitations

You cannot paste across multiple paste hierarchies.

Most, but not all ops support the “Pasted” primitive type. Those that do not will either ignore the hierarchical primitive or delete it.

Tips

Use the Paste op to create a continuous surface which covers multiple surfaces and seams by pasting a flat dense NURBS grid over the entire paste hierarchy with a parametric range of U=0-1, V=0-1. This makes for easier texturing as you avoid the problems associated with texturing over seams. You could also achieve a similar effect by running the geometry through aConvert SOP.

Example File

Look in: $HD/SOPs/Pasting/head.hip for an example file.

Parameters

Along Vector

Parametrically

As Is