Yue Wang wrote:
Hi,
an other issue is that patching whatever bit of tex coude should be done very careful; this has been proven by adding a backend ... rather strict control over extensions and changes is needed in order to keep tex's reputation of stability up; a one line change could result in for instance a rounding issue (i mention it because we ran into it some time ago) and can have rather drastic consequences; you don't want that to happen with a machinery that has to reproduce a document at the pixel level
a patch that might work on ones machine might eventually result in many problems all over the world if only because most users don't update frequently and depend on formal distributions (btw the same is true for fonts and other resources ... small changes can have huge consequences)
From my experience LuaTeX's result is very different from pdfTeX's result. The most notable one is that they give me different line breaks even with the same source and tfms given. Last time I was working on a Chinese translation of Karl's TeX for the Impatients, It occured to me that LuaTeX's linebreak is so different from pdfTeX's, and what's worse, LuaTeX gives me more overfull boxes. Of course, I use an old version of LuaTeX distributed in TeXLive 2008 (0.25.x, if memory serves). I doubt whether it will be possible for LuaTeX to produce the similar result as TeX does, (not to say pixel level).
we recenetly tested luatex (a more recent version than the one on tex live) with the texbook and there are only a few cases where we see differences, especially when ligatures occur at linebreaks; this is something that will be sorted out; 100% compatibility will never be reached because we use a slightly different route (separation of lig building, kerning, hyphenation and par building) but in practice this should not be a problem so, best use a recent version
But is compactability that important? XeTeX is not compatible with the
it is. of course there will be differences e.g. due to different hyphenation patterns (more complete since we have utf and > 256 chars can be used in patterns), and also because when using font some of traditional tex's limitations are gone (number of distinctive heights and depths) as well as some parameters in open type variants might differ which also leads to different spacing but in general, the expected behaviour of tex remains; there is so much macro code out there that we will not break anything in that respect (unless is can be easily compensated, like some of the removed pdftex primitives)
good old TeX, but it is still widely used in Asia (Here we don't use LuaTeX simply because there is no LaTeX package support). Knuth also
well, it's as with good old tex ... it will take a few years for everyone to catch up; when pdftex came around it took a while too before all features were supported by all macro packages; i'm not too worried about that a too fast change would also backfire on users; for context that's not so much an issue because they is is a beta-update infrastructure and most users are willing to use beta's but with latex you need to keep in mind that there are many users out there who depend on a real stable system (with no experimental stuff that breaks down your document processing every now and then)
suggested that there are several rounding flaws in recent version of TeX that he cannot change it, but he recommended that modern implementations change that (see TUGBoat, Volume 29 (2008) No.2).
maybe roundingproblems are less an issue in cjk fonts, but in for instance arabic typeetting, where many glyphs are pasted together by shifting it really matters; one scaled point might result in a .01bp shift in a pdf file which is visible to the sensitive eye Hans ----------------------------------------------------------------- Hans Hagen | PRAGMA ADE Ridderstraat 27 | 8061 GH Hasselt | The Netherlands tel: 038 477 53 69 | fax: 038 477 53 74 | www.pragma-ade.com | www.pragma-pod.nl -----------------------------------------------------------------