glow outline blendmode dragonruby

glow.rb

# one-time setup
@glow_dirs ||= 16.times.map do |i|
  a = i * Math::PI * 2 / 16
  [Math.cos(a), Math.sin(a)]
end
@glow_mask_blend ||= Numeric.compose_blendmode(
  BLENDFACTOR_ZERO, BLENDFACTOR_SRC_ALPHA, BLENDOPERATION_ADD,
  BLENDFACTOR_ZERO, BLENDFACTOR_SRC_ALPHA, BLENDOPERATION_ADD
)
@glow_hole_punch ||= Numeric.compose_blendmode(
  BLENDFACTOR_ZERO, BLENDFACTOR_ONE_MINUS_SRC_ALPHA, BLENDOPERATION_ADD,
  BLENDFACTOR_ZERO, BLENDFACTOR_ONE_MINUS_SRC_ALPHA, BLENDOPERATION_ADD
)
# additive that also accumulates alpha (blendmode_enum 2 leaves dst alpha at 0,
# which made the final composite invisible)
@glow_add ||= Numeric.compose_blendmode(
  BLENDFACTOR_SRC_ALPHA, BLENDFACTOR_ONE, BLENDOPERATION_ADD,
  BLENDFACTOR_ONE,       BLENDFACTOR_ONE, BLENDOPERATION_ADD
)
@glow_dirs  ||= [[1, 0], [-1, 0], [0, 1], [0, -1],
                 [0.7, 0.7], [-0.7, 0.7], [0.7, -0.7], [-0.7, -0.7]]
# @glow_rings ||= [[1.5, 200]]  # [offset radius px, alpha]; add [7, 60] back for a soft halo
@glow_rings ||= [[2, 255], [4, 255], [6, 180]]   # solid ~6px outline, fading at the rim
@glow_color ||= { r: 50, g: 230, b: 255 }

occluding = (@objects_in_viewport + @entities_in_viewport).select do |obj|
  obj.y < @player.y && Geometry.intersect_rect?(obj, @player)
end

if !occluding.empty?
  # player mask
  args.outputs[:glow_player].set w: 1280, h: 720, background_color: [0, 0, 0, 0]
  args.outputs[:glow_player].primitives.concat(
    @player.prefab.map { |spr| @camera.to_screen_space!(spr.dup) }
  )

  # occluder mask
  args.outputs[:glow_occ].set w: 1280, h: 720, background_color: [0, 0, 0, 0]
  args.outputs[:glow_occ].primitives.concat(
    occluding.flat_map(&:prefab).map { |spr| @camera.to_screen_space!(spr.dup) }
  )

  # hidden = player ∧ occluder (multiply whole RT by occluder alpha)
  args.outputs[:glow_hidden].set w: 1280, h: 720, background_color: [0, 0, 0, 0]
  args.outputs[:glow_hidden].primitives << { x: 0, y: 0, w: 1280, h: 720, path: :glow_player }
  args.outputs[:glow_hidden].primitives << { x: 0, y: 0, w: 1280, h: 720,
                                             path: :glow_occ, blendmode: @glow_mask_blend }

  # glow = dilated copies of hidden, interior punched out
  args.outputs[:glow_rt].set w: 1280, h: 720, background_color: [0, 0, 0, 0]
  @glow_rings.each do |radius, alpha|
    @glow_dirs.each do |dx, dy|
      args.outputs[:glow_rt].primitives << {
        x: dx * radius, y: dy * radius, w: 1280, h: 720, path: :glow_hidden,
        **@glow_color, a: alpha, blendmode: @glow_add
      }
    end
  end
  args.outputs[:glow_rt].primitives << { x: 0, y: 0, w: 1280, h: 720,
                                         path: :glow_hidden, blendmode: @glow_hole_punch }

  # composite onto the screen
  args.outputs.primitives << { x: 0, y: 0, w: 1280, h: 720,
                               path: :glow_rt, blendmode_enum: 2 }