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 21 def rollback raise RollbackTransaction end
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 33 def transaction snap = take_snapshot yield true rescue RollbackTransaction restore_snapshot(snap) false end
Rolls the page state back to the state of the given snapshot.
# File lib/prawn/document/snapshot.rb, line 61 def restore_snapshot(shot) page = state.page # Because these objects are referenced by identifier from the Pages # dictionary, we can't just restore them over the current refs in # page_content and current_page. We have to restore them over the old # ones. page.content = shot[:page_content].identifier page.content.replace shot[:page_content] page.dictionary = shot[:current_page].identifier page.dictionary.replace shot[:current_page] page.dictionary.data[:Contents] = page.content self.page_number = shot[:page_number] state.store.pages.data[:Kids] = shot[:page_kids].map{|id| state.store[id]} state.store.pages.data[:Count] = shot[:page_kids].size self.bounds = BoundingBox.restore_deep_copy(shot[:bounds], self) if shot[:dests] names.data[:Dests] = shot[:dests] end end
Takes a current snapshot of the document's state, sufficient to reconstruct it after it was amended.
# File lib/prawn/document/snapshot.rb, line 47 def take_snapshot # current_page holds a ref to the Pages dictionary which grows # monotonically as data is added to the document, so we share that # between the old and new copies. {:page_content => state.page.content.deep_copy, :current_page => state.page.dictionary.deep_copy(share=[:Parent]), :bounds => bounds.deep_copy, :page_number => page_number, :page_kids => state.store.pages.data[:Kids].compact.map{|kid| kid.identifier}, :dests => names? && names.data[:Dests].deep_copy} end