Re: widht vs. width in layout units

From: Martin Sevior (msevior@mccubbin.ph.unimelb.edu.au)
Date: Sun Apr 28 2002 - 05:38:38 EDT

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    On Sun, 28 Apr 2002, Tomas Frydrych wrote:

    >
    > Hi Martin,
    >
    > I was wondering whether in the rewrite of the layout engine we
    > might be able to get rid off the "screen width" / "layout width"
    > duality by doing all our width calculations at a very high resolution
    > and then scaling them down for screen operations. It seems to me
    > that most of our calculations are done in layout units anyway.
    > What do you think?
    >

    Hi Tomas,
             The only need for calculations at screen resolution is for laying
    our text into lines. If you use high resolution for on screen calculation
    different runs end up being overlapped. I'm sure you've seen this. This is
    a real problem especially with say an italic run being followed by a run
    of bold text.

    I'd kind of hoped that a sophisticated line layout system like
    Pango/Freetype could solve these issues and get kerning to work too. From
    your reading of these libraries do you if that is true?

    In addition we have issues with screen dirt since clearScreen clears
    rectangular areas and some italic fonts have pixels outside their
    rectangular enclosures. You and I have fought against this with special
    case code to detect this. I can think of several ways to improve this.

    My favourite is to clear one char ahead and behind a run the redraw just
    that character.

    This would allows us to have arbitary backgrounds like pixmaps or shading
    instead of just solid colour like now. The clearscreen method would just
    overwrite the background pixmap.

    We'd also have to worry about borders but that could be taken care of.

    Thomas Flecher suggested that layout should be done with floating point
    calculations. I think I prefer that screen and print layout is done at the
    one high resolution setting. If we do it right we're gaurenteed to get
    perfect WYSIWYG for lines per page. If we could find a way to make it work
    for horizontal text layout we'd get it for the width too.

    Anyway those are my thoughts. I'd be very interested in your ideas on
    these points.

    Cheers

    Martin

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