think-cell technical report TC2003/01 A GUI-based Interaction ...

5.2 An Application of Dynamic Programming IMPLEMENTATION
5.2 An Application of Dynamic Programming
Large parts of my implementation are relatively straight-forward compositions of
function calls, such as the control flow that generates a union set of all currently re-
quired UI objects (Fig. 39). In some cases, however, there was opportunity to apply
results from theoretical computer science. In this section, an implementation of the
dynamic programming approach is presented, that serves for optimal simultaneous
placement of multiple shapes.
5.2.1 The Gridline Matching Problem
When a slide is composed using Microsoft PowerPoint, common user actions like
copy/paste or move can be applied not only to single objects, but also to composi-
tions of multiple objects. In the traditional PowerPoint interface, such compositions
show static relationships and are handled just the same way as a single shape. This
is fine as long as the placement is purely pixel-oriented.
SOURCE
DEST
s 1 s 2 s 3 s 4 s 5
d 1 d 2 d 3 d 4 d 5 d 6
MergeGridlines(…)
SOURCE
DEST
Figure 41: Matching two lists of gridlines
d 1
s 1 s 2 s 3 s 4 s 5
d 2 d 3 d 4 d 5 d 6
The insertion of multiple elements into the smart grid was discussed in sec-
tion 4.3.2. The question arises, to which gridlines pasted shapes should be bound.
Trivially, the pasted shape or composition of shapes would preserve its internal
structure and proportions, and new gridlines would be generated wherever the
shapes’ edges fell. Since the slide layout is instantly rearranged by the solver,
the placement and the proportions of inserted shapes would be adapted, anyway.
Therefore, in the context of the smart grid, the precise pixel-based placement of
shapes is almost irrelevant. What counts is the order of the gridlines to which
shapes are bound. The multiple-placement problem in the smart grid boils down
to matching two sets of gridlines, which is illustrated in figure 41: The gridlines
from the source location of the pasted shapes may be identified with gridlines at
the destination, or may be placed between two consecutive destination gridlines.
This decision might not only affect a single shape, but would have an effect of the
overall composition of shapes that are inserted concurrently. For example, shapes
that are placed flush next to each other in the original location should probably
not be torn apart when they are inserted into another smart grid. On the other
hand, some stretching and bending might be necessary to meet the user’s intention;
imagine a table row whose contents are meant to fit the layout of another table.
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