Re: layout/screen units mess

From: Dom Lachowicz (
Date: Thu Aug 08 2002 - 13:21:31 EDT

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    > 1) Speed: here it's a draw. Contrary to common
    > knowledge, floating point operations are not a
    > bottleneck since the 486SX days, and for those
    > "machines FPU impaired" our speed is probably sucking
    > there anyway. A few years ago (at the pentium I rise)
    > rumors said that floating point calculations were
    > *faster* than integer calculations, because the
    > processor had more oportunities to parallelize
    > calculations

    On all of our major supported platforms (sparc, ia32, ppc), floating
    point operations are generally faster than most integer based
    operations. However, I'm not seeing this as so much of an issue.

    > 3) Pango: here integer calculations win (if we choose
    > the same units as pango). I'm not expecting that to
    > be a big deal with floating units, but I may be
    > biased.

    I'd like to think about this more when we actually get closer to using
    Pango for our layout needs. This might not be for another year or two
    (if at all), and it might not be too large of an issue.

    > 4) layout independance for the years to come: if we go
    > the integer units way, we prevent any numerical
    > problems. If we go the floating point way, slight
    > changes in the way we calculate something, may change
    > the result due to numerical instability, and thus it
    > may affect layout. Before you consider this point as
    > a fundamental one, take in account that we've already
    > changed the layout of the user documents from version
    > to version for much lamer reasons, and we've not
    > changed it in "subtle" ways, but in rather radical
    > ways.

    This isn't a *huge* problem. Word Processor documents are allowed to
    look (and layout) slightly differently between versions and between
    platforms. Of course, we should try to keep these differences at a
    minimum, but there are some other reasons why things can and will look
    differently no matter what we do:

    * Different fonts on different platforms (we don't and won't embed
    fonts like PDFs)
    * Slight/Major changes in the layout engine
    * Should we ever support leading and kerning properly

    I personally don't care if you use floats or integers, but please be
    consistent. I think that's more important than anything else.


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