TAPESTRY: The Art of Representation and Abstraction
Super-primitive
DEFINITION
A collection of primitives in a vector graphics program which have been associated in such a way that they behave, in many ways, as a single graphic object.
EXPLANATION
In order for the representation range of vector-graphic programs to be readily extensible for different drawing disciplines, it is desirable to include a "clumping" mechanism by which a set of simple primitives can be collected together and treated as a unit. For instance, a drafter might use a CAD program to draw a toilet (water-closet) as a series of lines and curves. Once complete, however, they may want to use that graphic in many places within a drawing (perhaps an apartment building floor plan). If the lines can be clumped together, they can be selected and placed at a later date, at a significant savings in time and data.
OPERATION
The user draws the initial graphic, either in the context of an evolving drawing, or in a separate data area. This is then given a name and a local origin (the point by which it will be placed in subsequent usage).
When the user want to place a copy (or instance) of this graphic at a later time, they reference it by name, indicate a location within the drawing, and (usually) set x, y, z scaling and/or rotation factors. This allows very generic graphics, such as trees, to be placed at differing sizes within the work.
BENEFITS
Most systems implement a "many-to-one" scheme, in which many uses (or instances) of the graphic all reference the same centralized definition. Two benefits accrue to this:
- This results in a more compact description of the data (since the instances require less data to store than the original data), and
- A change to the (single) definition immediately propagates to the instances. That is, the instances all change. In the case of modular, repetitive drawings, this makes it possible to replace simple representations with alternative or more complex representations at a later date, as better information becomes available.
In almost all systems the scale factors are applied uniformly, making it difficult to define a generic door or window graphic, complete with trim, which can be scaled to fit any opening. This is because the trim scales too!
EXAMPLES
This concept has been called many things, including BLOCKS, CELS, COMPONENTS and so on.
Last updated: April, 2014
