Bloody PDF boxes and cr*p marks!

[Henning Hraban Ramm via ntg-context <ntg-context@ntg.nl>]

Comrades!

There must have been a time when PDF boxes (i.e. CropBox, TrimBox, BleedBox) worked as they should, but it must have been a short time.
The wiki page https://wiki.contextgarden.net/PDF_Boxes is mostly a documentation of bugs and workarounds, but even that is not entirely correct (any more?).
I gave up on that subject and still fix the boxes with Acrobat Pro whenever I need them to be correct. But that’s no solution.
(And it’s probably also my fault, since I was one of those who wanted this implemented and then didn’t check enough if it does what it should.)

Ok, calm down, try again...

* MediaBox is supposed to be the biggest, i.e. print sheet.
* CropBox is the viewable area – usually same as MediaBox or TrimBox makes sense.
* BleedBox must be TrimBox plus bleed.
* ArtBox is neglectable for whole layouts (same as TrimBox might make sense), just interesting in \externalfigure.

According to PDF Standard, MediaBox is the only required one; but CropBox is the most important one, since PDF viewers rely on it.

With
\setuppaper[A4]
all boxes can be the same (or undefined). Status quo.

With
\setuppaper[A4][A4,oversized]
I’d expect ConTeXt to set...
* MediaBox and CropBox to the bigger format
* TrimBox to the page format (A4)
* BleedBox also to the page format, while no bleed is defined

Status quo: no additional boxes defined.

Beware, \showframe draws a green box at the paper size (supposed TrimBox), this is misleading in Acrobat Reader & Pro, where the TrimBox is shown in green (if this option is activated)!

Bleed is to be defined in \setuplayout:

\showframe
\setuppapersize[A4][A4,oversized]
\setuplayout[
  location=middle,
  bleedoffset=-5mm,
  marking=on,
]
%\setupinteractionscreen[width=max,height=max]

\starttext
X

\stoptext

Status quo: 
* works only with \setupinteractionscreen
* bleedoffset must be negative
* BleedBox is set, but not TrimBox (TB > BB is a nesting error)

Beware, \setupbleeding refers only to stretching of images (\externalfigure)!


This gives more or less correct results:
\setuplayout[
  location=middle,
  trimoffset=-7.5mm,
  bleedoffset=3mm,
  marking=on,
]

* still works only with \setupinteractionscreen
* negative trimoffset defines the TrimBox (actual page size), value is subtracted from sheet size.
* positive bleedoffset (internally added to trimoffset)
* to define trimoffset, I must know the difference between paper size and sheet size ("oversized" adds 15 mm).

I.e. ConTeXt “thinks” from the sheet size instead from the (IMO more natural) paper size.

For me, the more natural setup would be:
\setuplayout[
  trimoffset=0mm, % from the paper size outward
  bleedoffset=3mm, % same, independent of trimoffset
]
% ... and no dependency on interactionscreen!

So far, I ignored cropoffset.
The parameter in itself works as I expected it to: cropoffset=3mm decreases the visible area by 3mm on each side.
But it also moves the other boxes by that value!
IMO that makes no sense, CropBox can be completely independent of the other boxes!
It would be logical to use negative values here, since the size decreases, in opposite to my suggested handling of the other parameters.

Yes, that would mean a backward incompatible change. But how many of us rely on the strange current behavior?
Please let us fix this!


In some cases it makes sense to have different values on e.g. inner and outer edges; I feat that would add a plethora of additional parameters (leftbleedoffset, innerbleedoffset...).
Maybe give a list like in CSS? bleedoffset={3mm,3mm,3mm,0mm} – top, right, bottom, left order implied; not very “ConTeXt style”.


Hraban




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