Class: RGame::Engine::WorldView

Inherits:
Node2D
  • Object
show all
Defined in:
lib/rgame/engine/world_view.rb

Overview

The node that marks where world space begins.

view = scene.add_node(WorldView.new)
view.add_node(player)     # draws at its own world coordinates

Its children live in world coordinates and are drawn once per active viewport: for each one, clip to that viewport's rectangle and translate by its camera, then run the same subtree again. Everything outside a WorldView is screen space and draws once.

That is the whole of split-screen, and it is why the transform and clip stacks in Core are proper push/pop stacks — a clip always narrows, so a child can never draw outside the region its parent allowed.

The subtree does not know how many times it is drawn

Children draw at their own absolute origin and never see a camera. This node supplies the view, so the same world serves one player or four with nothing below it changing — which is exactly what a camera owned by a node inside the world could not do, and why cameras belong to players.

Only draw multiplies, and deliberately

control and update still run once for this subtree, however many viewports draw it. That is what keeps simulation cost independent of player count, and it is also a safety property: a world node's on_update is where mutation belongs, so per-view updating would move an actor at twice the speed with two players — correctly in single player, silently wrong the moment somebody joins.

It does make the standing "draw renders state" rule load-bearing rather than stylistic: a draw with a side effect now happens once per player, and an allocation in one costs that many times.

A node that genuinely needs per-view work at draw time can read system(Viewports).views itself. Anything needing per-view state over time — a screen shake, a hit flash — is per-player rather than per-view, and belongs on that player's camera or their own subtree, which tick once.

Instance Attribute Summary

Attributes inherited from Node2D

#abs_angle, #abs_band, #abs_input_owner, #abs_x, #abs_y, #angle, #band, #children, #components, #context, #height, #input_owner, #parent, #paused, #scene, #sibling_order, #width, #x, #y, #z

Instance Method Summary collapse

Methods inherited from Node2D

#add_component, #add_node, #children_unsorted!, #control, #enter_tree, #exit_tree, #freed?, #get_component, #in_tree?, #on_add, #on_control, #on_draw, #on_remove, #on_update, #queue_free, #remove_component, #remove_node, #root, #sweep_freed, #system, #update

Methods included from Signal::DSL

#signal

Constructor Details

#initialize ⇒ WorldView

World content, which is the default anyway — stated because this is the node that marks where world space begins, and a reader looking for "which band is the world in" should find the answer here.



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# File 'lib/rgame/engine/world_view.rb', line 47

def initialize(**)
  super(band: :world, **)
end

Instance Method Details

#draw(renderer, _view = nil) ⇒ Object

Drawn once per viewport, so this overrides the whole of draw rather than just draw_children: the node's own visuals belong inside the viewport too, not once outside all of them.

view is the screen-space view this node was reached with, and is deliberately ignored — a WorldView asks the system which viewports exist rather than being told, so a game can place one anywhere in the tree.



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# File 'lib/rgame/engine/world_view.rb', line 58

def draw(renderer, _view = nil)
  viewports = system(Viewports)
  viewports.views.each do |world_view|
    renderer.clipped(world_view.x, world_view.y, world_view.width, world_view.height) do
      renderer.translated(world_view.offset_x, world_view.offset_y) do
        super(renderer, world_view)
      end
    end
  end
end