Draw Buffering for Dragon Ruby

app.rb

class DrawBuffer
  attr_accessor :primitives, :outputs, :render_targets

  def initialize
    @primitives = []
    @render_targets = {}
  end

  def [](key)
    @render_targets[key] = [] if !@render_targets.has_key?(key)
    @render_targets[key]
  end

  def []=(key, value)
    @render_targets[key] = value
  end

  def flush
    @render_targets.each do |key, value|
      @outputs[key].primitives.concat(value)
    end

    @outputs.primitives.concat(@primitives)
    @primitives = []
    @render_targets = {}
  end
end

def tick(args)
  args.state.draw_buffer ||= DrawBuffer.new
  draw_buffer = args.state.draw_buffer
  draw_buffer.outputs = args.outputs

  draw_buffer.primitives << {
    x: args.grid.w / 2,
    y: args.grid.h / 2,
    text: "Hello World"
  }.label!

  render_target = args.outputs[:render_target]
  render_target.w = 200
  render_target.h = 40

  draw_buffer.primitives << {
    x: args.grid.w / 2,
    y: (args.grid.h / 2) - 80,
    w: 200,
    h: render_target.h,
    path: :render_target
  }

  draw_buffer[:render_target] << {
    x: 0,
    y: 0,
    anchor_y: -0.5,
    text: "Hello from a render target"
  }.label!

  draw_buffer.flush
end