Prawn::Document#on_page_create in v 1.3.0

[BrentWheeldon]

Hi there,

We have some code that does, effectively:

document = Prawn::Document.new(...)
# stuff
document.on_page_create do |doc|
 # more stuff
end

Since upgrading to 1.3.0 we get: NoMethodError: undefined method 'on_page_create' for #<Prawn::Document:0x007f92f8a88fd0> when running this code. I checked the changelog, but didn't see anything about this method, and I can't see it in the source anymore. I can see it that it's been removed from lib/prawn/document/internals.rb in b48b206, but it's not clear if there's an alternative?

Any help would be greatly appreciated!

[practicingruby]

@BrentWheeldon:

on_page_create is a low-level method that's not part of the public API. (repeat or number_pages are often used instead). If those support your use case, I'd recommend using them instead. If not, please let me know what you're using on_page_create for, so we can think about how to support your use case.

But an immediate fix for 1.3 would be to call renderer.on_page_create, just don't assume it's going to be a stable API.

[BrentWheeldon]

Thanks for the quick reply, @sandal!

We're basically abusing that private API to keep track of which "section" we're in inside of a report to render that in a header. This is some inherited code that inherited so I've not dig in too deep. I'll see if we can do this in a supported way.

[practicingruby]

@BrentWheeldon: This may be something we could offer support for (or build a tiny extension for) in the future. See this thread for what I think is a reasonably clean solution: https://groups.google.com/forum/#!topic/prawn-ruby/_KIg4Ih8TdU

[practicingruby]

Here's a direct link to the relevant code sample: https://groups.google.com/d/msg/prawn-ruby/_KIg4Ih8TdU/MaHBtDu2F4sJ

[mojavelinux]

We also use this method in Asciidoctor PDF to paint the background color of the page.

https://github.com/asciidoctor/asciidoctor-pdf/blob/master/lib/asciidoctor-pdf/converter.rb#L96

Is there another way to accomplish this?

[practicingruby]

@mojavelinux:

Maybe not, because repeaters run last, so the z-index is going to be wrong (your background would be rendered on top of the page contents rather than behind them).

I'm convinced that restoring on_page_create as a public method on Prawn::Document is reasonable. Anyone is welcome to prepare a patch. (It should simply delegate to renderer.on_page_create, which is the workaround for 1.3.x)

[practicingruby]

@mojavelinux: Also, we should think about what first-order support for setting background colors might look like, since it's a tedious operation currently. A patch or feature-request ticket for that is welcome!

[mojavelinux]

@sandal Thanks for the clarification / input. I'll give it some thought when I upgrade Asciidoctor PDF to the latest Prawn.

[mikesax]

We've also been using on_page_create to prepare a page and create background graphics. It would be nice to either have on_page_create back, or to have a feature that lets repeaters optionally run before the main content is rendered, so the z-order is correct. For example:

pdf.repeat(:all, before: true) do
   ...
end

[practicingruby]

@mikesax. For the short term, I'd definitely like to bring back on_page_create. Controlling the order of when repeat calls get run is an interesting idea... I'll have to think on that some more.

[nathansamson]

document.on_page_create do |doc|
 # more stuff
end

Obviously only works for the second page and later, unless you do pass skip_page_creation: true on document creation...

So even if on_page_create is resurected it feels a bit clunky... Repeaters with different z-indexes sounds nice though

[practicingruby]

@nathansamson: Yeah, in time for the next release I'm only going to restore the behavior because that's how it's been since basically forever, but that is a good wart to think about dealing with when we produce a better alternative in the future.

[jessedoyle]

@practicingruby - I submitted PR #825 that delegates the method call to renderer. Hopefully we can get this in the 2.0.0 release!

[practicingruby]

Merged!

[bousquet]

👍 Thanks. Used this today in combination with prawn-svg for crisp background image underneath flowing text.