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

3.2 Computer Supported Layout STATE OF THE ART
As another example, Macromedia Director allows objects to have a size and
position independently from the grid unit. When snap-to-grid is active and an object
is moved by drag-and-drop, the location where the mouse cursor grabs the object
determines the part of the object that is aligned with the grid. This correlation is
made explicit by visual feedback.
As we have seen in section 2.1.5 (item B), the Microsoft PowerPoint implemen-
tation of a regular grid as an alignment tool is seriously flawed.
Guidelines. Magnetic guidelines are another popular tool that often works well
when a layout requires horizontal and vertical alignment but does not fit into the
regular structure of a grid. Guidelines behave like gridlines, except that they are
explicitly placed by the user at arbitrary positions. Again, the implementation of
guidelines in Microsoft PowerPoint is unnecessarily limited.
Align and Distribute. In most popular software for interactive layout, including
Microsoft PowerPoint, the frequent alignment operations are available as toolbar
buttons. These typically cover the alignment of the top, bottom, left, or right border
of the selected objects, where the object with topmost top border (or bottom, left,
right, respectively) usually is immutable and the other objects are aligned. Also,
middle (vertical) or center (horizontal) alignment is supported. The alignment
operations mentioned always apply to only one dimension (horizontal or vertical)
at a time. For alignment to be available, at least two objects must be selected.
A related operation is distribute, which takes three or more objects and dis-
tributes the space between them evenly while the two outmost objects are im-
mutable. Again, this operation works only horizontally or vertically at a time.
3.2 Computer Supported Layout
Substantial work has been done in computer supported drawing and layout, the
roots of this field of research dating back as far as to Sutherland’s Sketchpad [Sut63].
All of these attempts have a tradeoff in common between the complexity of the input
specification and the expressiveness of the system in terms of flexibility and accuracy
of output. Interactive drawing aids generally use simpler input (namely, direct
manipulation) than entirely automated systems. The latter often aim at reusing
the same layout specification (usually provided in textual code) for multiple sets
of content and to reuse the same content in different environments (e. g., different
screen resolutions).
3.2.1 Interactive Drawing Aids
There has been some research on computer support for precise freehand drawing
that overcomes the very restricted concept of a regular grid (cf. Sect. 3.1.2). Bier
and Stone [BS86] propose a concept they call snap-dragging, which maintains the
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