How to start a new page inside a tag?

[Ayush1325]

Okay, So I am creating a big PDF programmatically but it seems pagebreak can only be used at the top level. So how can I start a new page if I am inside a list or maybe a chapter? Are there tags or something for section? Or maybe I can just use chapter for whatever requires a new page inside a chapter? I want to get the auto numbering the way we get in chapters and list. I know I can just do it programmatically and just use all the top-level elements, but I would like to know if there is a better solution.

[yogthos]

Doing it programmatically would be the way to go at the moment. I'm open to adding the feature if it is supported by the openpdf API though. I won't have time to look in the near future, but I can help with a PR for this.

[Ayush1325]

Ok, thanks. I will work on it if possible.

[Ayush1325]

Ok, so I tried the rudimentary approach of using a global doc variable and create a new page by (.newPage doc) but that does not seem to work inside the :section render method (does work with :pagebreak). Also there seem to be doc-events in the core.clj:

(defn doc-events [^PdfWriter pdf-writer
                  {:keys [on-document-open
                          on-document-close
                          on-page-start
                          on-page-end
                          on-chapter-start
                          on-chapter-end
                          on-paragraph-start
                          on-paragraph-end
                          on-section-start
                          on-section-end
                          event-handler]}]
  (if event-handler
    (.setPageEvent pdf-writer ^PdfPageEventHelper event-handler)

    (when (not-empty (remove nil? [on-document-open
                                   on-document-close
                                   on-page-start
                                   on-page-end
                                   on-chapter-start
                                   on-chapter-end
                                   on-paragraph-start
                                   on-paragraph-end
                                   on-section-start
                                   on-section-end
                                   event-handler]))
      (.setPageEvent
        pdf-writer
        ^PdfPageEventHelper
        (proxy [PdfPageEventHelper] []
          (onOpenDocument [^PdfWriter writer ^Document doc]
            (when on-document-open
              (on-document-open writer ^Document doc)))

          (onCloseDocument [^PdfWriter writer ^Document doc]
            (when on-document-close
              (on-document-close writer doc)))

          (onStartPage [^PdfWriter writer ^Document doc]
            (when on-page-start
              (on-page-start writer doc)))

          (onEndPage [^PdfWriter writer ^Document doc]
            (when on-page-end
              (on-page-end writer doc)))

          (onChapter [^PdfWriter writer ^Document doc position ^Paragraph title]
            (when on-chapter-start
              (print "New Chapter")
              (on-chapter-start writer doc position title)))

          (onChapterEnd [^PdfWriter writer ^Document doc position]
            (when on-chapter-end
              (on-chapter-end writer doc position)))

          (onParagraph [^PdfWriter writer ^Document doc position]
            (when on-paragraph-start
              (on-paragraph-start writer ^Document doc position)))

          (onParagraphEnd [^PdfWriter writer ^Document doc position]
            (when on-paragraph-end
              (on-paragraph-end writer doc position)))

          (onSection [^PdfWriter writer ^Document doc position depth ^Paragraph title]
            (when on-section-start
              (on-section-start writer doc position depth title)))

          (onSectionEnd [^PdfWriter writer ^Document doc position]
            (when on-section-end
              (on-section-end writer doc position))))))))

and it has a section on-section-started, but it seems to be called with all nil arguments, at least in the debugger, so what's up with that?

[yogthos]

Hmm, not sure why you're not seeing the arguments. If I run the following, I'm seeing what's expected:

(pdf
   [{:on-section-start (fn [writer doc position depth title]
                         (println "args:" writer doc position depth title))}
    [:chapter "chapter"
     [:section "Section Title" "Some content"]]]
   "doc.pdf")

=> args: #object[com.lowagie.text.pdf.PdfWriter 0x5dec2391 com.lowagie.text.pdf.PdfWriter@5dec2391] #object[com.lowagie.text.pdf.PdfDocument 0x58b3e0e com.lowagie.text.pdf.PdfDocument@58b3e0e] 791.0 2 #object[com.lowagie.text.Paragraph 0x51e758c4 [1.1. , Section Title]]

[Ayush1325]

Hmm, not sure why you're not seeing the arguments. If I run the following, I'm seeing what's expected:

(pdf
   [{:on-section-start (fn [writer doc position depth title]
                         (println "args:" writer doc position depth title))}
    [:chapter "chapter"
     [:section "Section Title" "Some content"]]]
   "doc.pdf")

=> args: #object[com.lowagie.text.pdf.PdfWriter 0x5dec2391 com.lowagie.text.pdf.PdfWriter@5dec2391] #object[com.lowagie.text.pdf.PdfDocument 0x58b3e0e com.lowagie.text.pdf.PdfDocument@58b3e0e] 791.0 2 #object[com.lowagie.text.Paragraph 0x51e758c4 [1.1. , Section Title]]

Ok, thanks. I was trying to pass it the wrong way. I will try to see if I can use that in some way to start a new page, although I think it might not be possible to do with quick tricks since even directly adding (.newPage doc) in the subtags doesn't seem to work. Maybe will have to see if openpdf supports it.

[yogthos]

Yeah, I think you'll have to check what openpdf can do here, and then we can expose that API.

[Ayush1325]

Can confirm, using (.newPage doc) in the on-section-start seems to work, even with subsections. That makes me wonder why it doesn't work using a global variable or something.

[yogthos]

It's likely dependent on the state of the doc. So, it sounds like it's possible to use on-section-start to trigger page breaks then, but you have to manually figure out what section you're in and whether you want to do a page break or not.

[Ayush1325]

Yeah, I can do it easily for my particular case, but don't really know any general implementation since the on-section-start function doesn't really get any meta of section either, just the title and numbering.

[yogthos]

Looks like that's the best approach at the moment, glad to hear it solves your use case.