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

4.1 A New Approach to Slide Layout INTERACTION CONCEPT
the 2-dimensional total ordering of the smart elements is also specified by the smart
grid. Finally, gridlines serve to represent the constraints that are exported by the
smart elements bound to them, in particular preferred and minimum sizes.
Two minor modifications are required to tailor this interpretation of the smart
grid for practical use: Firstly, white space between elements plays an important
role in the visual appearance of a slide and must be preserved. Therefore, some
smart elements have a built-in margin surrounding them. Furthermore, I use an
explicit gap smart element which can be inserted into the smart grid to request an
additional amount of white space. Secondly, the total ordering of gridlines must be
weakened, because a total ordering of shapes is not always intended. For example,
shapes that reside in independent areas of a slide may well be moved and sized
independently, if this leads to a better layout.
Further constraints that help to abstractly specify layout intentions can be rep-
resented by the smart grid. For instance, the user can pin a gridline to a certain
position, meaning that the solver must leave those gridline’s position untouched.
Another option is to select a group of gridlines and require equable spacing between
them.
Constraints That Cannot Be Expressed by a Grid
An analysis of a large number of slides from the target application domain showed
that grid-oriented constraints do not suffice to express all frequently used layout
intentions. In order to make the system applicable for a reasonably large set of
use cases, support must be provided for certain constraints between elements that
are not necessarily related through the grid. This includes constant proportions
between the sizes of two elements – 1:1 (same size) in most cases –, as well as same
style, same color, same font size and the like.
Constraints Spanning Multiple Slides
In contrast to other grid-based layout systems (e. g., Feiner’s GRIDS [Fei88]), the
smart grid is not fix but dynamically changes to reflect the requirements of the
contained shapes. Unlike the guidelines in plain Microsoft PowerPoint, which have
global scope, the smart grid is primarily a tool for local layout of a single slide. The
concept, however, could easily be extended with inter-slide constraints and thus the
smart grid could also support a uniform layout across a set of slides or an entire
presentation.
A priori, gridlines in the smart grid have a scope local to the current slide. To
support some kind of master layout that applies uniformly to each slide, it suffices to
introduce the concept of global gridlines: Gridlines that appear at the same position
on each slide. Positions of global gridlines cannot be optimized by local constraint
solving; therefore, to the solver global gridlines appear just as pinned gridlines. As
of now, global gridlines are not yet part of the prototype implementation.
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