Prawn::Document::Snapshot

Constants

RollbackTransaction

Public Instance Methods

rollback() click to toggle source

Call this within a transaction block to roll back the transaction and prevent any of its data from being rendered. You must reset the y-position yourself if you have performed any drawing operations that modify it.

    # File lib/prawn/document/snapshot.rb, line 22
22:       def rollback
23:         raise RollbackTransaction
24:       end
transaction() click to toggle source

Run a block of drawing operations, to be completed atomically. If rollback is called or a RollbackTransaction exception is raised inside the block, all actions taken inside the block will be rolled back (with the exception of y-position, which you must restore yourself).

Returns true on success, or false if the transaction was rolled back.

    # File lib/prawn/document/snapshot.rb, line 34
34:       def transaction
35:         snap = take_snapshot
36:         yield
37:         true
38:       rescue RollbackTransaction
39:         restore_snapshot(snap)
40:         false
41:       end

Private Instance Methods

restore_snapshot(shot) click to toggle source

Rolls the page state back to the state of the given snapshot.

    # File lib/prawn/document/snapshot.rb, line 59
59:       def restore_snapshot(shot)
60:         # Because these objects are referenced by identifier from the Pages
61:         # dictionary, we can't just restore them over the current refs in
62:         # page_content and current_page. We have to restore them over the old
63:         # ones.
64:         page.content = shot[:page_content].identifier
65:         page.content.replace shot[:page_content]
66: 
67:         page.dictionary = shot[:current_page].identifier
68:         page.dictionary.replace shot[:current_page]
69:         page.dictionary.data[:Contents] = page.content
70: 
71:         @page_number = shot[:page_number]
72: 
73:         @page_number = shot[:page_number]
74: 
75:         @store.pages.data[:Kids] = shot[:page_kids].map{|id| @store[id]}
76:         @store.pages.data[:Count] = shot[:page_kids].size
77: 
78:         if shot[:dests]
79:           names.data[:Dests] = shot[:dests] 
80:         end
81:       end
take_snapshot() click to toggle source

Takes a current snapshot of the document’s state, sufficient to reconstruct it after it was amended.

    # File lib/prawn/document/snapshot.rb, line 48
48:       def take_snapshot
49:         {:page_content    => Marshal.load(Marshal.dump(page.content)),
50:          :current_page    => Marshal.load(Marshal.dump(page.dictionary)),
51:          :page_number     => @page_number,
52:          :page_kids       => @store.pages.data[:Kids].map{|kid| kid.identifier},
53:          :dests           => names? && 
54:                              Marshal.load(Marshal.dump(names.data[:Dests]))}
55:       end

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