[Officeshots] Pixelwise comparison of pdf files

[Milos Sramek]

Dňa 25.06.2011 23:16, Thomas Zander  wrote / napísal(a):
> On Friday 24 June 2011 18.09.42 Milos Sramek wrote:
>> Regarding the consistency:
>>> The ODF standard does not require this consistency, but many expect it
>>> anyway,
>> I do not understand. Does this mean that there is some level of
>> variability allowed, in the sense of HTML, which allows to render
>> differently in various environments?
> ODF itself defines the data and it gives hints for representation.  The issue 
> of consistency comes with text; ODF doesn't include the requirement of exact 
> glyph positioning.
> In practice each application will have a complete different codebase for 
> reading fonts, merging fonts, applying hinting and rasterizing the fonts to 
> an on-screen representation. This is not an exact science and little 
> differences will occur.
I understand. In the attached document this is visible nearly everywhere
- but no one (except for specialists) will notice if it were not
overlayed. This is a clear sign of using different rendering engines.

This means that there is a threshold between what is OK and what to
regard as a bug. In the attached picture, I think, there are four
differences which are well visible:
the bold underline, which seems to be thin in one case, the "crossed
out" text, which is in one case striked through, the size of the
superscript and subscript fonts and the underlined hyperlink.

Do you think that these are also within the limits of the "flexibility"
of the standard, or these are really bugs?

Milos
> When I say its not an exact science its also important to know that different 
> font rendering engines have different goals.  For print LaTex is known to be 
> the best one and that one is also extremely specific to only doing (slow) 
> text layout for print.
> I'm using Qts text rendering and have coded parts of that engine. Qts engine 
> is also used for on-screen display and has to be really fast.  So accuracy 
> may be scarified for speed.
>
> So, in ODF we don't have a requirement that each line breaks at exactly the 
> same point or that each page breaks at the same point either because if we 
> did we would essentially not allow different text engines to be used.
>
> Point of interest; you may have a chapter that is described in ODF. It has 
> so many words and has a specific font and size etc.
> In OOo that text may end up being 3 pages and 3 words.
> In Latex the engine could have 3 pages and 3 lines too but then choose to go 
> back over those 3 pages and adjust the inter-character spacing slightly on 
> some lines.  The end result would be that the text fits in 3 pages.  Which 
> would look a lot better :)
>
> This kind of innovation is allowed in ODF just *because* we don't have the 
> requirement.  As such I think its a good thing.

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