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268 lines
7.6 KiB
268 lines
7.6 KiB
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
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<html>
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<head>
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<meta content="text/html; charset=ISO-8859-1" http-equiv="content-type">
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<title>KSpread Painting</title>
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</head>
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<body>
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<h1>KSpread Painting</h1>
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<p>This file describes how the painting of a spreadsheet works and is
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supposed to work. At present, it is not a complete description.</p>
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<h2>General</h2>
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<p>Painting is started by KSpreadCanvas::paintUpdates(). This method
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calls paintCell() on all visible cells, i.e. it always repaints the
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entire sheet. This is inefficient, but is OK for most circumstances.
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There is a bug in bugzilla (#xxxx) which points this out.</p>
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<p>Each cell can paint itself. If a number of cells are explicitly
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merged by the user, then the merged cell is painted by a single call
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to paintCell() on its upper left corner cell, the "master" cell of the
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merged group. If paintCell() is called on any of the other cells in
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the group, a recursive call to paintCell is done on the master cell.
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<br>
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<b>NOTE</b>: This is not yet implemented.</p>
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<p>If the content of a cell is wider than the cell itself, then we say
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that this cell <i>overflows</i> and expands into its neighbors (see
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<b>Layout</b> below). Currently this only happens for cells that are
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unmerged. Cells that are merged never expand, but instead show a
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<i>more text</i> marker. See more details about overflow below.</p>
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<p>A border between cells is painted twice:
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<ul>
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<li>When the cell on one side of the border is drawn.
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<li>When the cell on the other side is drawn.
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</ul>
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</p>
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<h2>Layout</h2>
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<p>Painting is a two-step process. First, makeLayout() is called, which
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analyzes the content of the cell and checks if it fits into the cell.
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If it doesn't, two things can happen:</p>
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<ol>
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<li>The cell will be painted with a <i>more text</i> marker (a red
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arrow).
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<li>If the cell is left aligned and the cell to the right is empty,
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the cell can <i>expand</i> into the right cell and obscure it
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with the content of this cell. If the cell is right aligned,
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the text can overflow to the left instead. (This is currently
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slightly buggy.)
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</ol>
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The layout code also takes into account if the cell has vertical text,
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if it is angled, indented text, and so on.</p>
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<p>The result of the layout process is the setting of the following
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variables in a cell:</p>
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<table cellspacing="0" cellpadding="3" border="1">
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<tr>
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<th colspan="2">Values that are calculated during the paint process</th>
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</tr>
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<tr>
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<td><pre>d->textX<br>d->textY</pre></td>
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<td>Text position within the cell</td>
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</tr>
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<tr>
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<td><pre>d->textWidth<br>d->textHeight</pre></td>
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<td>The size of the text</td>
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</tr>
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<tr>
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<td><pre>d->fmAscent</pre></td>
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<td>Ascent value of the font metrics</td>
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</tr>
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<tr>
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<td><pre>d->extra()->extraXCells<br>d->extra()->extraYCells</pre></td>
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<td>Number of extra cells in X and Y direction</td>
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</tr>
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<tr>
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<td><pre>d->extra()->extraWidth<br>d->extra()->extraHeight</pre></td>
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<td>Extra width/height brought in by the extra cells</td>
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</tr>
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<tr>
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<td><pre>d->extra()->nbLines</pre></td>
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<td>Number of lines if multirow</td>
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</tr>
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<tr>
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<td><pre>d->strOutText</pre></td>
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<td>The text that is shown in the cell.</td>
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</tr>
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</pre>
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</table>
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<p>After the layout process, paintCell() uses these
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variables to position the text within the cell and also to paint "more
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text" markers, etc.</p>
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<p>The value of extra[XY]Cells and extraWidth/Height can be made non-zero
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in two ways:</p>
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<ol>
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<li>The cell is the master cell of a merged group.
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<li>The content is too wide/high, and the cell has expanded into
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neighboring cells.
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</ol>
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<p>Currently these two cases never occur simultaneously. That might
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change in the future. So, as for now the two cases can be separated by
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checking if d->extra()->merged[XY]Cells are zero (case 2) or non-zero
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(case 1).</p>
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<h2>Overflow</h2>
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<p>In this context, the word <i>overflow</i> means that the content of
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a cell is wider than the cell itself. In that case, the extra space
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that is demanded can be handled in several different ways:</p>
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<ul>
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<li>The content can be partially shown, i.e. cut.
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<li>The content can overflow into neighbor cell(s). Which cells that
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are affected is dependent on alignment, if the neighbors are
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empty, etc, etc. </ul>
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<h3>Borders and overflow</h3>
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<p>A border that is defined for a cell should never be moved just
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because the content of the cell overflows. The current version
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(1.4beta1) does that, but it has to be changed.</p>
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<h3>Other spreadsheets</h3>
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<p>Here follows a survey of how a number of spreadsheet programs
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handle overflow into other cells.</p>
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<table cellspacing="0" cellpadding="3" border="1">
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<tr>
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<th colspan="2">Case</th>
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<th>Excel</th>
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<th>Gnumeric</th>
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<th>Oocalc</th>
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<th>KSpread 1.4<br><i>(Check these!)</i></th>
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<th>Suggested behaviour</th>
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</tr>
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<tr>
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<td rowspan="2"><b>Text in cell<br>Left aligned</b></td>
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<td><i>Empty cell TtR</i></td>
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<td>Overflows into cell TtR</td>
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<td>Overflows into cell TtR</td>
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<td>Overflows into cell TtR</td>
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<td>Overflows into cell TtR</td>
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<td>Overflows into cell TtR<br><b>OK</b></td>
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</tr>
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<tr>
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<td><i>Non-empty cell TtR</i></td>
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<td>Text is cut<br>no mark</td>
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<td>Text is cut<br>no mark </td>
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<td>Text is cut<br>arrow TtR </td>
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<td>Text is cut<br>arrow TtR </td>
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<td>Text is cut<br>arrow TtR<br><b>OK</b></td>
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</tr>
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<tr>
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<td rowspan="3"><b>Text in Cell<br>Right aligned</b></td>
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<td><i>Empty cell TtL</i></td>
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<td>Overflows into cell TtL</td>
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<td>Overflows into cell TtL</td>
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<td>Overflows into cell TtL</td>
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<td>Text is cut<br>arrow TtR</td>
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<td>Overflows into cell TtL</td>
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</tr>
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<tr>
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<td><i>Non-empty TtL<br>empty TtR</i></td>
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<td>Text is cut<br>no mark</td>
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<td>Text is cut<br>no mark</td>
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<td>Text is left aligned(!),<br>overflows into cell TtR</td>
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<td>Text is cut<br>arrow TtR</td>
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<td>Text is cut<br>arrow TtR<br><b>OK</b></td>
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</tr>
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<tr>
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<td><i>Non-empty TtL<br>non-empty TtR</i></td>
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<td>Text is cut<br>no mark</td>
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<td>Text is cut<br>no mark</td>
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<td>Text is left aligned(!),<br>cut<br>arrow TtR</td>
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<td>Text is cut<br>arrow TtR</td>
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<td>Text is cut<br>arrow TtR<br><b>OK</b></td>
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</tr>
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<tr>
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<td rowspan = "2"><b>Number in cell<br>Alignment doesn't matter</b></td>
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<td><i>Generic format</i></td>
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<td>Precision is reduced</td>
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<td>Precision is reduced</td>
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<td>"###" is shown</td>
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<td>#############<br>(cell is filled)</td>
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<td>#############<br>(For now)<br>Preciesion is reduced<br>(Long term)</td>
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</tr>
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<tr>
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<td><i>Number format</i></td>
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<td>#############<br>(cell is filled)</td>
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<td>#############<br>(cell is filled)</td>
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<td>"###" is shown</td>
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<td>#############<br>(cell is filled)</td>
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<td>#############<br>(cell is filled)</td>
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</tr>
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<tr>
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<td rowspan="2"><b>Border and overflow<br>left aligned</b></td>
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<td><i>Text format<br>ordinary cell</i></td>
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<td>??</td>
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<td>Right border is not drawn<br>Text overflows TtR</td>
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<td>Border stays on cell<br>Text overflows TtR<br>Text covers right border</td>
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<td>??</td>
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<td>Border stays on cell<br>Text overflows TtR<br>Text covers right border</td>
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</tr>
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<tr>
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<td><i>Text format<br>merged cell</i></td>
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<td>??</td>
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<td>Gnumeric 1.2.8 can't merge<br>Test with Gnumeric 1.4</td>
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<td>Border stays on cell<br>Text is cut</td>
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<td>??</td>
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<td>Border stays on cell<br>Text is cut(?)</td>
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</tr>
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</table>
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<p></p>
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<table cellspacing="0" cellpadding="3" border="1">
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<tr>
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<th colspan="2">Legend</th>
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</tr>
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<tr>
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<td>LA</td><td>Left Aligned</td>
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</tr>
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<tr>
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<td>RA</td><td>Right Aligned</td>
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</tr>
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<tr>
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<td>TtR</td><td>To the Right</td>
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</tr>
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<tr>
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<td>TtL</td><td>To the Left</td>
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</tr>
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</body>
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</html>
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