We truncate the position of the line in GraphicsContext::drawLineForText, this gives correct results as long as the coordinates coming in are integer. If we enable SUBPIXEL_LAYOUT however the positions coming in will often be fractions of pixels leading to bad rounding.
Created attachment 195070 [details]
Comment on attachment 195070 [details]
Clearing flags on attachment: 195070
Committed r146878: <http://trac.webkit.org/changeset/146878>
All reviewed patches have been landed. Closing bug.