calibre-devs team mailing list archive

[Kovid Goyal <kovid@xxxxxxxxxxxxxx>]

Given the level of variability in input sources/viewers I doubt we'll ever 
reach a universally satisfactory solution. I'm inclined to just stick with the 
CSS spec, assume a default base font size of 12pt/16px (96dpi) for all viewers 
and convert all specified font sizes into % units. This isn't likely to be 
much worse than any other solution and is likely to be the most "future proof" 
going forward. This is what html2epub does now.

The remaining question is how to improve font size rescaling. 

Kovid. 

On Thursday 18 December 2008 18:30:11 Marshall T. Vandegrift wrote:
> Hi all / Kovid:
>
> So I'm trying to create a more robust system for rationalizing
> CSS-specified font sizes, including the "key" based system I described
> in an earlier thread.  There are three main causes of headaches:
>
>   (1) Different display engines have different base font-sizes for text
>       which doesn't have a 'font-size' specified in its inheritance
>       chain.
>   (2) Different display engines map the CSS logical font sizes
>       ('xx-small', 'x-small', etc.) to different actual sizes.
>   (3) Different display engines vary their base and logical sizes
>       differently in response to user-selected zoom levels.
>
> Here's a table showing logical font sizes for various readers at various
> zoom levels (The data are formatted: <base size>, [<xx-small size>,
> <x-small size>, <medium size>, etc.])
>
>   Sony Reader / Adobe DE
>   small:     9.0, [ 5.5,  6.0,  7.5,  9.0, 11.5, 15.0, 15.0]
>   medium:   12.0, [ 7.5,  9.0, 10.0, 12.0, 15.5, 20.0, 20.0]
>   large:    16.0, [10.0, 11.0, 13.5, 16.0, 21.0, 26.0, 26.0]
>   * The initial zoom in the desktop version of Adobe DE corresponds to
>     "large" on the Reader.
>
>   MSReader
>   smallest: 11.0, [ 7.0, 10.0, 11.0, 13.0, 16.0, 18.0, 20.0]
>   small:    13.0, [10.0, 11.0, 13.0, 16.0, 18.0, 20.0, 22.0]
>   medium:   14.0, [11.0, 13.0, 14.0, 16.0, 18.0, 22.0, 26.0]
>   large:    16.0, [13.0, 15.0, 16.0, 18.0, 22.0, 26.0, 28.0]
>   largest:  18.0, [14.0, 16.0, 18.0, 22.0, 26.0, 28.0, 30.0]
>
>   Firefox 3 / Gecko
>   100%:     12.0, [ 5.0,  7.0,  9.0, 12.0, 13.5, 17.0, 17.0]
>   * Gecko appears to scale even fixed-sized fonts with zoom level,
>     although by a factor not in lock-step with the logical sizes.
>
>   ebook-viewer / WebKit
>   default:  14.5, [ 9.5, 11.0, 13.5, 14.5, 18.5, 23.0, 23.0]
>   * WebKit also appears to scale even fixed-sized fonts with zoom level,
>     and again not in lock-step with the logical sizes.
>
> I haven't profiled Mobipocket yet, although IIRC it only supports the
> HTML 4.0 <font size="[1-7]/> format, which will make doing so annoying
> at the very least.
>
> Anyway, what I'm getting at is that to convert font sizes properly, a
> conversion/generation process needs to be aware of the logical sizes of
> both the source and destination formats/viewers.  This is especially
> true when the source content uses the viewer-provided base font size or
> mixes any of base-derived font-sizes, logical font-sizes, or fixed
> font-sizes (all of which I have alas seen in commercial LIT e-books).
>
> A secondary problem is which zoom-level to target.  When during
> conversion targeting one of the viewers which do not vary the size of
> fixed-sized fonts with zoom-level, in order to make the resulting book
> zoomable, it is necessary to use the logical font sizes as a base /
> bases in some fashion.  This means picking a zoom-level to target as the
> "default" at which the fonts will be as close to the source /
> user-specified sizes as possible.
>
> </babbling>, thoughts?
>
> -Marshall
>
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-- 
_____________________________________

Kovid Goyal  MC 452-48
California Institute of Technology
1200 E California Blvd
Pasadena, CA 91125

cell  : +01 626 390 8699
office: +01 626 395 6595 (449 Lauritsen)
email : kovid@xxxxxxxxxxxxxxxxxx
web   : http://www.kovidgoyal.net
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