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< Ferreteria‎ | v0.5‎ | layout
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Ferreteria: layout system: event subsystem


The event objects allow element objects in a layout element tree to coordinate their actions. Each event object corresponds to a particular event; an event is triggered in an object by calling OnEvent() with an event-object of the appropriate class. Core events are triggered in this order:

1. cEventNodeBuild: create any subsidiary nodes which might themselves need to receive events
2. cEventNodeFigure: do any calculations involving other nodes (which will have been created by this point)
  • This allows, for example, the number of visible twigs to be calculated before rendering. Some elements may only display themselves if they have at least one visible twig -- or may display differently if they don't.
    • ...although that kind of process could probably be done without an event-system. One that can't, however, is where one element needs to access another one that is outside of its branch, to read or write data. There needs to be a means of ensuring that all required nodes will have been created by a certain point, and the layout system's event-subsystem is what does that.
    • The event-subsystem also provides an unambiguous waystation for ensuring that those calculations (which may be relatively expensive) are done exactly once.
3. cEventNodeRender: assemble the string representing the markup for the object's appearance within the output (typically the screen, but in theory could also be a document or even audio markup of some kind).

The core event objects are defined in layout/elem/event.php.



  • OnEvent() calls OnEventLocal()
  • ShouldDoTwigs(): protected function ShouldDoTwigs() : bool
    • Action: Determine whether events (including rendering) should be passed down to twigs. This typically returns a flag that is set during the calculations event.
  • Dispatch methods -- these each default (in tExecutableTwig) to a stub which does nothing:


Much of this usage is defined/modeled in cElement.

  • FetchRendered() returns the value set by StoreRendered() (which clears the stored value to prevent duplicate output)
  • RenderOutput(): public function RenderOutput() : string
    • Action: Assemble the entirety of the object's output, including any twigs.
  • RenderValue(): protected function RenderValue() : string
    • Action: Assemble the object's own output (separate from twig outputs).
  • RenderBranch(): protected function RenderBranch() : string:
    • Action: Assemble the twig outputs, applying any whole-list formatting (e.g. <ul>) or conditionals.
  • RenderTwigs(): protected function RenderTwigs() : string
    • Action: Assemble the basic twig outputs, applying any list-item formatting (e.g. <li>.

The canonical/typical method tree for rendering:


  • 2022-07-21 The Render*() events are now less deeply integrated into the dispatch process but still may end up with some interdependencies, so it's best to use the canonical names where applicable.
  • 2022-07-18 Scrapping some pieces of the current refactoring attempt.
    • Renamed:
      • OnCreateElements() → OnBuild()
      • OnRunCalculations() → OnFigure()
    • Rendering calculations will be done during OnFigure() instead of OnRender().
    • OnRender() now returns the output of FetchRendered().
      • Formerly: "This is the method called by the rendering event. It defaults (in tExecutableTwig) to a stub which does nothing."