DLI Implementation and Reference Guide - Datalogics

7.2 DLI Implementation and Reference Guide
What are Containers?
Concepts and Facilities: Guide to the DL Pager Composition System
Container may be a misleading name. These structures “contain” text and drawing
commands in the meaning of structure or hierarchy, but they do not have a limited
geometry in the sense of edges or boundaries. They “contain” text in data processing
terms, but are not visual constructs like lines and columns, and hence are not
containers in the typographic sense.
The best way to think of these structures is as a boundless plane. This plane may be
positioned, rotated, or scaled relative to the media on which the text will eventually be
imaged. There is no restriction on the order or placement of things within a container.
That is, within the container you are not constrained to move from left to right, or top
to bottom. Nor are you limited to the quadrant that is the range of positive values.
Negative positions within the plane may be used as well as positive positions.
You may use as many containers within a page as you wish, and they may be
positioned in any way. There is an overhead for the use of a container, however, and
keeping the number small is desirable.
The simplest use of containers is to create one for each page, and leave it positioned at
its default location and rotation. In this case, drawing on the plane and drawing on
the page are identical operations. The default configuration of a plane is
• positioned with its origin at the lower left hand corner of the media
• scaled 1.0 in both horizontal and vertical directions
• oriented with positive values of X proceeding to the right
• oriented with positive values of Y proceeding upward
Often, an existing composition engine will use other positioning. For instance, if your
engine assumes that (0, 0) is the upper left hand corner of the page and positive values
of leading proceed down the page, then repositioning the container will allow you to
use the X/Y values you have already calculated without changing them.
DLI contains three calls that will permit you to modify the location, scaling or
rotation of a container (and its content) relative to a page. These may be used at any
time before a container is committed to a page. Other transformations (mirroring,
shearing, etc.) may be accomplished by directly modifying the field AreaXform