lyx_mirror/00README_STR_METRICS_BRANCH
Jean-Marc Lasgouttes 059de2d04c Fix getColumnNearX for nested insets
The horizontal position of the inset was not taken in account.
The rounding is not always the same as with the old code, but this
is not really important.

Additional changes:

 * improve debug output of rows

 * remove Bidi& argument of the RowPainter constructor, since it is always
   an empty Bifi that is passed. This means that the Bidi class is not
   used at all any more in TextMetrics.cpp. The only remaining user is
   RowPainter.
2014-06-25 17:55:30 +02:00

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This branch is where I (jmarc) try to implement string_wise metrics
computation. This is done through a series of cleanups. The goal is to
have both good metrics computation (and font with proper kerning and
ligatures) and better performance than what we have with
force_paint_single_char.
Currently everything is supposed to work for LTR text, and RTL text
should work too except possibly metrics with Arabic and Hebrew fonts.
We'll see what to do after some feedback.
What is done:
* Make TextMetrics methods operate on Row objects: breakRow and
setRowHeight instead of rowBreakPoint and rowHeight.
* Change breakRow operation to operate on text strings on which
metrics are computed. The list of elements is stored in the row
object in visual ordering, not logical.
* Re-implement cursorX and getColumnNearX using row elements.
* Implement proper string metrics computation (with cache), when
lyxrc.force_paint_single_char is false. In this case, remove also
useless workarounds which disable kerning and ligatures.
Next steps needed:
* check what happens with arabic and/or hebrew text. There may be some
problems related to compose characters. I suspect that some code is
needed in FontMetrics::width.
Next possible steps:
* Get rid of old code in cursorX and getColumnNearX; it has been
kept for comparison purpose, guarded with KEEP_OLD_METRICS_CODE in
order to check computations.
* Re-implement row painting using row elements. This is not difficult
in principle, but the code is intricate and needs some careful
analysis.
* Profile and see how performance can be improved.
Difference in behavior (aka bug fixes)
* end of paragraph markers metrics are computed with the font of the
actual text, not default font.
* When cursor is after a LTR separator just before a RTL chunk, the
cursor position is computed better with the new code.
Other differences (aka real bugs)
* there are still difference in what breaks words. In particular,
RowPainter breaks strings at: selection end, spellchecking
extremity.