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/**
\page styleStorage Style Storage
\author Ariya Hidayat (<a href="mailto:ariya@kde.org">ariya@kde.org</a>)
\date 2004
\par Status:
FINISHED; NEEDS UPDATE (R-Tree, RectStorage)
<p>Formatting specifies how a cell should look like. It involves font
attributes like bold or italics, vertical and horizontal alignment,
rotation angle, shading, background color and so on. Each cell can have
its own format, but bear also in mind that a whole row or column format
should also apply.</p>
<p>Current way of storing formatting information is rather inefficient:
pack it together inside the cell. The reason is because most of cells
are either very plain (no formatting) and/or only have partial attribute
(e.g. only marked as bold, no font family or color is specified).
Therefore the approximately 20 bytes used to hold formatting information
are quite a waste of memory. Even worse, this requires that the cell
must exist even if it is not in use. As illustration, imagine a worksheet
where within range A1:B20 only 5 cells are not empty. When the user
selects this range and changes the background color to yellow, then
those 5 cells must store this information in their data structure but
how about the other 35 cells? Since the formatting is attached to the cell,
there is no choice but to create them. Doing this, just for the sake of
storing format, is actually not really good.</p>
<p>A new way to store formatting information is proposed below.</p>
<p>For each type of format a user can use, we have the corresponding
<i>formatting piece</i>, for example "bold on", "bold off",
"font Arial", "left-border 1 px", etc. Whenever the user
applies formatting to a range (could also be a whole column, row, or worksheet),
we save appropriate respective formatting piece in a stack. Say the user has
marked column B as bold, row 2 as italics, and set range A1:C5 with
yellow background color. Our formatting stack would look like:
</p>
<table cellspacing="0" cellpadding="3" border="1">
<tr>
<td><b>Range</b></td>
<td><b>Formatting Piece</b></td>
</tr>
<tr>
<td>Column B</td>
<td>Bold on</td>
</tr>
<tr>
<td>Row 2</td>
<td>Italics on</td>
</tr>
<tr>
<td>A1:C5</td>
<td>Yellow background</td>
</tr>
</table>
<p>Now let try to figure out the overall format of cell B2. From the first
we know it should be bold, from the second it should be italics, and last
it should have yellow background. This complete format is the one which
we used to render cell B2 on screen. In similar fashion, we can know that
cell A1 on the other only specifies the yellow background, because the first
and second pieces do not apply there.</p>
<p>Another possible way to see the format storage is by using 3-D perspective.
For each formatting piece, imagine there is a surface which covers the
formatted range (the xy-plane). The formatting information is simply attached
to the surface (say, as surface attribute). Every surface is stacked together,
its depth (the z-axis) denotes the sequence, i.e. the first surface is the
deepest. For the example above, we can view the pieces as one surface specifies
"bold on" which is a vertical of column B, one surface specifies
"italics on" which is a horizontal band of row 2 and one last surface
which specifies "yellow background" stretched in the range A1:C5.
How to find complete format for A2? This is now a matter of surface
determination. Traversing in the direction of z-axis from B2 reveals
that we hit the last and second surfaces only; thereby we can know the complete
format is "italics, yellow background".</p>
<p>It is clear that a format storage corresponds to one sheet only. For each
sheet, there should be one format storage. Cells can still have accessors to
its formatting information, these simply become wrapper for proper calls to the
format storage. Since each formatting piece holds information about the applied
range, we must take care that the formatting storage is correctly updated
whenever cells, rows or columns are inserted and deleted.</p>
<p>In order to avoid low performance, we must use a smart way to iterate over
all formatting pieces whenever we want to find out complete format for given
cell(s). When the sheet gets very complex, it is likely that we will have
many many formatting pieces that are not even overlap. This means, when we
need formatting of cell A1, it is no use to check formatting pieces of range
Z1:Z10 or A100:B100 which do not include cell A1 and are even very far from A1.
One possible solution is to arrange the formatting pieces in a quad-tree.
Because one piece can cover a very large area, it is possible that it will
be in more than one leaf in the quad-tree. <i>Details on the possible use of
quad-tree or other methods should be explored further more</i>.</p>
*/
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