commit 7b73ff262e3c7ad251ef883a396405b20c6d3ece
author Paul Pazderski <paul-eclipse@ppazderski.de> Thu Nov 12 19:08:56 2020 +0100
committer Paul Pazderski <paul-eclipse@ppazderski.de> Tue Nov 17 03:35:37 2020 -0500
tree 3cf493583bda7d33ec54a3c04a37027c5d520304
parent 8c27c639129c90ddc8ed0ede0085479d23116028

Bug 568740 - [Win32] TextLayout renders underscore, strikeout and border
only on last line

Each of the three styles underscore, strikeout and border are rendered
separately in there own method. TextLayout implementation for windows
tries to optimize rendering of those styles by drawing adjacent styles
in one a single call. (for border it also looks much better)
It will test if two adjacent style parts (separate for underscore,
strikeout and border) are 'adherent' which seem to mean they look the
same. This can happen for once if the user supplies suboptimal styles,
i.e. the same or an equal style instance for adjacent ranges instead of
one style for the whole range at once. But even if adjacent styles are
different it will still try to optimize rendering if a specific substyle
is equal, e.g. two adjacent styles got different fonts but both use
underline with the same color. In this case it will draw the underline
in one call for both ranges.

Now for the failing case. If a style expands over more than one line
TextLayout will internally split those styles on line delimiter because
it renders per line. This will include a separate StyleItem for the line
delimiter to mark it as lineBreak which inherits the style of the range
before. An example. The two lines content "abc\n123" with an underline
over the hole range produce internally three StyleItems all with same
style.
While drawing the first line it will see underline for the "abc" part
but postpone rendering because the adjacent style for "\n" has the same
underline style. But line breaks are rendered differently so the
postponed underline drawing will never happen.

Change-Id: Ic19f13a559c79d148f62fc7944101dd59ae17dde
Signed-off-by: Paul Pazderski <paul-eclipse@ppazderski.de>