Re: Understanding the eps bounding box (rounding)

[Urs Liska]

Hello Karl,


Am 02.03.2018 um 01:25 schrieb address@hidden:
> In my
>
>   PostScript Language
>   Document Structuring
>   Conventions Specification
>   Adobe Developer Support
>   Version 3.0
>   25 September 1992
>
> possible downloadable from
>   https://archive.org/details/ps-doc-struc-conv-3
>
> it says:
>
> %%BoundingBox: { <llx> <lly> <urx> <ury> } | (atend)
>                 <llx> ::= <int>                       (Lower left x coordinate)
>                 <lly> ::= <int>                       (Lower left y coordinate)
>                 <urx> ::= <int>                       (Upper right x coordinate)
>                 <ury> ::= <int>                       (Upper right y coordinate)
>                 This comment specifies the bounding box that encloses all marks 
> painted
>                 on all pages of a document. That is, it must be a "high water 
> mark" in all
>                 directions for marks made on any page. The four arguments 
> correspond to
>                 the lower left (llx, lly) and upper right corners (urx, ury) of 
> the bounding box
>                 in the default user coordinate system (PostScript units). See 
> also the
>                 %%PageBoundingBox: comment.
>
> I.e., according to spec, the numbers describe a box that encloses
> everything. It doesn't say it must the smallest such box.
> Same thing for PageBoundingBox.

I think it *is* the smallest box, but truncated to integers. At least I 
can't imagine a box that leaves full units empty.
From what I've seen so far I was confident that the numbers correspond 
to what LilyPond sees as \pt, and also in LaTeX I have treated the 
numbers as pt (as opposed to bp).

Could this be an issue here?

> That is in contrast to:
>
> PostScript language reference manual, 3rd ed, TABLE 5.3:
>
> FontBBox array (Required) An array of four numbers in the glyph coordinate 
> system giving
>                 the left, bottom, right, and top coordinates, respectively, of 
> the font bounding
>                 box. The font bounding box is the smallest rectangle enclosing 
> the shape that
>                 would result if all of the glyphs of the font were placed with 
> their origins co-
>                 incident, and then painted. This information is used in making 
> decisions
>                 about glyph caching and clipping. If all four values are 0, the 
> PostScript inter-
>                 preter makes no assumptions based on the font bounding box.
>
> where they specify the smallest one, but for fonts and other
> parts of pages, not whole pages.

Interestingly, here they don't specify the data type of the numbers.

> ...
> > Does the -80 mean:
> >
> >    * any value between -79 and -80
> >    * any value between -79.5 and -80.4999999
> ...
>
> So, if the leftmost painted things is at e.g. -79.1 then llx <= -80,
> since llx >= -79 wouldn't do.

Thank you. This makes sense but is exactly the kind of assumption I 
didn't want to approach by trial & error.

Best
Urs

> Regards,
> /Karl Hammar
>
> -----------------------------------------------------------------------
> Aspö Data
> Lilla Aspö 148
> S-742 94 Östhammar
> Sweden
> +46 173 140 57
>
>
>
> _______________________________________________
> lilypond-user mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/lilypond-user