Re: Line Spacing Calculations

> On 26 Aug 2016, at 20:14, Nate Bellowe <nathanb@windward.net> wrote:
>
> Hello! One quick irrelevant thing before the real post…
>  
> The mailing list bot sent out an email that contained a broken link:
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Changed
rgds
jan I.

>  
> On to the real email:
>  
> Hopefully I’m not bothering you too much! Sorry to intrude on your dev mailing list, this may 
> seem a little off topic, but I have been banging my head on this forever, and I know you guys are 
> the experts!  We can also all get some help out of this, perhaps!
>
> I have been running into an issue that I know the developers of libreOffice have likely faced 
> before! I was wondering if the developers that have worked on this before would like to talk some 
> about this, I'd really appreciate it!
>
> Basically, I have some questions on how to calculate the line spacing between lines, when parsing 
> and rendering a docx file.
>
> My requirement is to exactly match Word, not necessarily the OOXML spec, in the spacing between 
> lines in a simple paragraph.
>
> In order to try to do this, I have built a tool to analyze the differences between my layout and 
> Word's layout. To do so it does the following:
>
> - First it generates a (or many) docx files.
> - Next it creates pdfs from the docx files. It uses Word to render the docx to PDF, and my 
> program to render the docx to PDF. "word.pdf", and "me.pdf"
> - Then it analyzes the resulting PDFs for differences in layout.
>
> So, my tool would say:
>
> - Create a document "template.docx" with 1000 "a" characters in a single run of text with the 
> same properties.
> - Make a "word.pdf" and "me.pdf" from this docx
> - Calculate info from the pdfs, in particular, calculating the line spacing in terms of the 
> calculated leading between a lines ascent and the previous lines descent (our (Ascent + Descent) 
> are identical-ish, so all that differs is the whitespace between lines). I often think of it as 
> the lines whitespace...
>
> This tool showed me that the leading varies greatly from font to font.
>
> To depict this, I used the tool to make thousands of these comparisons, in particular generating 
> for:
>
> - For each font in system
> - For "a", "y", and a mix of letters and spaces.
> - For different font sizes.
> - For different line spacing types (Single, One and a half, and Double)
>
> I was hoping to find groupings, such as "this type of font has 1.3 times my calculation of 
> leading". 
>
> I was able to conclude far less than I had hoped, and was wondering if you could help me further 
> with the issue of calculating line spacing. I'm providing you with a file that is best downloaded 
> and opened using the filters in the header row. Note that its not totally complete, there are 
> missing entries, but I doubt they will be a problem for anyone, and I'm going to regenerate it 
> soon but its pretty slow, so I'm finishing up some changes to it first.
>
> Here is a comparison of the layout of our software, vs the layout of Word's for every font 
> installed on my system, etc. (attached and linked)
> https://drive.google.com/file/d/0BzQpUdPjnJUUclRXVXFkaEh3Mms/view?usp=sharing
>
> I'm not positive, but I believe the issue could be one of the following:
>
> - Word is using a different process than we are to calculate the "leading" of a font. We don't 
> parse the font files ourselves, instead rely on libraries to get font sizing information, and 
> perhaps in the "world of font files" I am missing something, and word is parsing the fonts 
> directly and differently.
> - Word has some sort of lookup table that handles groups of fonts, or an algorithm, that scales a 
> fonts leadings up or down based on some criteria I am unaware of.
> - Word is using an additional criteria besides leading, ascent, and descent, to determine line 
> spacing.
>
> Please feel free to email me at nathanb@windward.net
>
> Thank you so much for your time!!
>  
> I know you guys aren’t trying to emulate Word, (I very much enjoy Writer) but am sure you’ve had 
> complaints of people opening documents made in Word that there friend sent them, and having major 
> formatting differences, such as different pagination.
>  
> Microsoft is famous for having been both open and closed about this spec, and thus allowing its 
> wide-spread adoption without proper competition, and I think that openness between communities 
> trying to work with that is very helpful. We’d be happy to exchange information about quirks and 
> things that differ from the spec that we find.
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