layout/screen units mess

From: Tomas Frydrych (
Date: Thu Aug 08 2002 - 09:55:12 EDT

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    I feel very strongly that before we start even putting out betas for
    version 2 we have to get rid of the screen/layout units dichotomy.
    The fact that we do some layout calculations in screen units and
    some layout calculations in layout units, coupled with the way we
    scale font metrics from one to the other, is responsible for probably
    over 90% of our wysiwyg bugs. We have been trying hard to fix
    many of these for long time, and we are just running in circles.

    The paradox of it all is that, AFAIK, there is no real reason why we
    would need both sets of units and at places we just shamelessly
    scale from one to the other.

    What I am proposing is that we remove both sets of units and
    replace them with a single unit system identical to the one used by
    Pango, where there are 1024 units to a screen pixel. This makes it
    possible to quickly translate the internal units to screen units and
    vice versa using shifts, and would provide us with a precision rougly
    15 times greater than our layout units do. It would also make the
    eventual transition to Pango simpler.

    This would also result in a substantial performance improvement, for
    measuring character widths is one of the bottlenecks and having
    single set of units would reduce the processing to half.

    Now, if anyone has a good reason for keeping to coordinate
    systems, then please speak up now.


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