KSpread Painting

This file describes how the painting of a spreadsheet works and is supposed to work. At present, it is not a complete description.

General

Painting is started by KSpreadCanvas::paintUpdates(). This method calls paintCell() on all visible cells, i.e. it always repaints the entire sheet. This is inefficient, but is OK for most circumstances. There is a bug in bugzilla (#xxxx) which points this out.

Each cell can paint itself. If a number of cells are explicitly merged by the user, then the merged cell is painted by a single call to paintCell() on its upper left corner cell, the "master" cell of the merged group. If paintCell() is called on any of the other cells in the group, a recursive call to paintCell is done on the master cell.
NOTE: This is not yet implemented.

If the content of a cell is wider than the cell itself, then we say that this cell overflows and expands into its neighbors (see Layout below). Currently this only happens for cells that are unmerged. Cells that are merged never expand, but instead show a more text marker. See more details about overflow below.

A border between cells is painted twice:

Layout

Painting is a two-step process. First, makeLayout() is called, which analyzes the content of the cell and checks if it fits into the cell. If it doesn't, two things can happen:

  1. The cell will be painted with a more text marker (a red arrow).
  2. If the cell is left aligned and the cell to the right is empty, the cell can expand into the right cell and obscure it with the content of this cell. If the cell is right aligned, the text can overflow to the left instead. (This is currently slightly buggy.)
The tqlayout code also takes into account if the cell has vertical text, if it is angled, indented text, and so on.

The result of the tqlayout process is the setting of the following variables in a cell:

Values that are calculated during the paint process
d->textX
d->textY
Text position within the cell
d->textWidth
d->textHeight
The size of the text
d->fmAscent
Ascent value of the font metrics
d->extra()->extraXCells
d->extra()->extraYCells
Number of extra cells in X and Y direction
d->extra()->extraWidth
d->extra()->extraHeight
Extra width/height brought in by the extra cells
d->extra()->nbLines
Number of lines if multirow
d->strOutText
The text that is shown in the cell.

After the tqlayout process, paintCell() uses these variables to position the text within the cell and also to paint "more text" markers, etc.

The value of extra[XY]Cells and extraWidth/Height can be made non-zero in two ways:

  1. The cell is the master cell of a merged group.
  2. The content is too wide/high, and the cell has expanded into neighboring cells.

Currently these two cases never occur simultaneously. That might change in the future. So, as for now the two cases can be separated by checking if d->extra()->merged[XY]Cells are zero (case 2) or non-zero (case 1).

Overflow

In this context, the word overflow means that the content of a cell is wider than the cell itself. In that case, the extra space that is demanded can be handled in several different ways:

Borders and overflow

A border that is defined for a cell should never be moved just because the content of the cell overflows. The current version (1.4beta1) does that, but it has to be changed.

Other spreadsheets

Here follows a survey of how a number of spreadsheet programs handle overflow into other cells.

Case Excel Gnumeric Oocalc KSpread 1.4
(Check these!)
Suggested behaviour
Text in cell
Left aligned
Empty cell TtR Overflows into cell TtR Overflows into cell TtR Overflows into cell TtR Overflows into cell TtR Overflows into cell TtR
OK
Non-empty cell TtR Text is cut
no mark
Text is cut
no mark
Text is cut
arrow TtR
Text is cut
arrow TtR
Text is cut
arrow TtR
OK
Text in Cell
Right aligned
Empty cell TtL Overflows into cell TtL Overflows into cell TtL Overflows into cell TtL Text is cut
arrow TtR
Overflows into cell TtL
Non-empty TtL
empty TtR
Text is cut
no mark
Text is cut
no mark
Text is left aligned(!),
overflows into cell TtR
Text is cut
arrow TtR
Text is cut
arrow TtR
OK
Non-empty TtL
non-empty TtR
Text is cut
no mark
Text is cut
no mark
Text is left aligned(!),
cut
arrow TtR
Text is cut
arrow TtR
Text is cut
arrow TtR
OK
Number in cell
Alignment doesn't matter
Generic format Precision is reduced Precision is reduced "###" is shown #############
(cell is filled)
#############
(For now)
Preciesion is reduced
(Long term)
Number format #############
(cell is filled)
#############
(cell is filled)
"###" is shown #############
(cell is filled)
#############
(cell is filled)
Border and overflow
left aligned
Text format
ordinary cell
?? Right border is not drawn
Text overflows TtR
Border stays on cell
Text overflows TtR
Text covers right border
?? Border stays on cell
Text overflows TtR
Text covers right border
Text format
merged cell
?? Gnumeric 1.2.8 can't merge
Test with Gnumeric 1.4
Border stays on cell
Text is cut
?? Border stays on cell
Text is cut(?)

Legend
LALeft Aligned
RARight Aligned
TtRTo the Right
TtLTo the Left