Post by @hipsterelectron@circumstances.run

@hipsterelectron@circumstances.run 2 mo. ago

i have learned just moments ago that the adobe portable document format is yet another rebranding of the same tarball slop we have been tossing around for half a century

(7.5.6) Incremental Updates

The contents of a PDF file can be updated incrementally without rewriting the entire file. When updating a PDF file incrementally, changes shall be appended to the end of the file, leaving its original contents intact.

NOTE 1: The main advantage to updating a file in this way is that small changes to a large document can be saved quickly. There are additional advantages:

> In certain contexts, such as when editing a document across an HTTP connection or using OLE embedding (a Windows-specific technology), a conforming writer cannot overwrite the contents of the original file. Incremental updates may be used to save changes to documents in these contexts.

NOTE 2: The resulting file has the structure shown in Figure 3. A complete example of an updated file is shown in H.7, "Updating Example". — (7.5.6) Incremental Updates The contents of a PDF file can be updated incrementally without rewriting the entire file. When updating a PDF file incrementally, changes shall be appended to the end of the file, leaving its original contents intact. NOTE 1: The main advantage to updating a file in this way is that small changes to a large document can be saved quickly. There are additional advantages: > In certain contexts, such as when editing a document across an HTTP connection or using OLE embedding (a Windows-specific technology), a conforming writer cannot overwrite the contents of the original file. Incremental updates may be used to save changes to documents in these contexts. NOTE 2: The resulting file has the structure shown in Figure 3. A complete example of an updated file is shown in H.7, "Updating Example".

12 Replies

5 Boosts

d@nny disc@

@hipsterelectron@circumstances.run 2 mo. ago

https://hackers.town/@zwol/114158568811964745 over a year ago, @zwol immediately identified the PDF as the epitome of design that optimizes for the derivative with not a moment for the integral

d@nny disc@

@hipsterelectron@circumstances.run 2 mo. ago

that tweet from yesteryear reached out to answer my lingering question: "did they really call it a production-quality document format and then stuff everything of note at the end?"

yes! because stuffing extra data after the original document the domain experts signed off on is where you can add special features

the swagon

@dragon@lesbian.solutions 2 mo. ago

@hipsterelectron what do you mean by optimizing for the derivative rather than the integral?

d@nny disc@

@hipsterelectron@circumstances.run 2 mo. ago

@dragon it's a really really pretentious way to say it but i'm referring to control theory and the canonical PID controller used in that field

PID controller

control loop mechanism used in control engineering based on three terms (P, I and D)

~22 more replies

d@nny disc@

@hipsterelectron@circumstances.run 2 mo. ago

@dragon i am specifically thinking about how this category of architecture (stuffing shit at the end of a stream without any cross-referencing) feeds the microsoft/google pathology of shipping a half-assed feature quickly (e.g. an incremental edit, which is nonstandard but only occurs with special software, which isn't fully-specified) that further imperils the ability to extract structured data from documents that people put an immense degree of effort and willpower into creating

d@nny disc@

@hipsterelectron@circumstances.run 2 mo. ago

@dragon i'm thinking of lawyers and mathematicians

d@nny disc@

@hipsterelectron@circumstances.run 2 mo. ago

@dragon and HTML is not better, because to do anything declarative you need CSS properties, and CSS properties means using a whole fucking w3c web browser

and my impetus here is actually not about rendering a document to pixels, but about indexing its information

d@nny disc@

@hipsterelectron@circumstances.run 2 mo. ago

@dragon if you read the alt-text for OP you will see my valiant attempt to represent the structure of the screenshotted document excerpt with that old rusty knife, unadorned ASCII whitespace

d@nny disc@

@hipsterelectron@circumstances.run 2 mo. ago

@dragon not only are there 2-3 ways to even represent text mapped to a pdf, but you absolutely are not allowed to just edit the text by hand. this is something i learned from the tesseract project (which google acquired from someone who gave a shit), in which tesseract is the only program that can modify the text layer (and it doesn't accept human input)

d@nny disc@

@hipsterelectron@circumstances.run 2 mo. ago

there's this delectable bit of circumlocution right after the screenshot:

A cross-reference section for an incremental update shall contain entries only for objects that have been changed, replaced, or deleted. Deleted objects shall be left unchanged in the file, but shall be marked as deleted by means of their cross-reference entries.

they don't even garbage-collect. you can in fact append an operational transform over the document contents with absolutely zero global indexing and the viewer won't detect a thing until their reader comes upon your change!

Nora Reed

@nora@blob.love 2 mo. ago

@hipsterelectron i did understand this bit and lol that sucks so bad

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d@nny disc@

@hipsterelectron@circumstances.run 2 mo. ago

The added trailer shall contain all the entries except the Prev entry (if present) from the previous trailer, whether modified or not. In addition, the added trailer dictionary shall contain a Prev entry giving the location of the previous cross-reference section (see Table 15). Each trailer shall be terminated by its own end-of-file (%%EOF) marker.

that's right: IT'S YET ANOTHER TURING MACHINE!!!

1+ more replies