Supersampling for even rotation of odd sized sprites

main.rb

# supersampling for fancy sprite rotation
# solves uneven rotation of odd-sized sprites
# using an upscaled render target

def tick(args)
  args.state.size ||= 7 # width/height of sprite (odd)
  args.state.upsample ||= 8 # 2 minimum, 8 is better
  args.state.path ||= 'sprites/rotate5.png' # path to sprite

  args.state.upsample_size ||= args.state.size * args.state.upsample

  args.outputs[:supsam].w = args.state.upsample_size
  args.outputs[:supsam].h = args.state.upsample_size

  # normal rotation on the left

  normal_rotation = {
    x: 56,
    y: 35,
    w: args.state.size,
    h: args.state.size,
    path: args.state.path,
    angle: args.tick_count
  }.sprite

  # fancy rotation on the right

  args.outputs[:supsam].primitives << {
    x: 0,
    y: 0,
    w: args.state.upsample_size,
    h: args.state.upsample_size,
    path: args.state.path,
    angle: args.tick_count
  }

  fancy_rotation = {
    x: 66,
    y: 35,
    w: args.state.size,
    h: args.state.size,
    path: :supsam,
  }.sprite

  # borders around sprites to show the center drift

  borders = [
    {
      x: 55,
      y: 34,
      w: 9,
      h: 9,
    }.border,
    {
      x: 65,
      y: 34,
      w: 9,
      h: 9,
    }.border
  ]

  # magnifies output purely to make the result easier to see
  # send directly to outputs.sprites|primitives under normal conditions

  args.outputs[:enlarger].primitives << [ 
    normal_rotation, 
    fancy_rotation,
    borders,
  ]

  args.state.magnification ||= 10
  args.outputs.sprites << {
    x: 0, 
    y: 0, 
    w: args.grid.w * args.state.magnification,
    h: args.grid.h * args.state.magnification,
    path: :enlarger
  }

  # labels 
  args.outputs.labels << {
      x: 640,
      y: 460,
      text: "Normal    Fancy",
      alignment_enum: 1
    }
end