rotating mask

main.rb

module Main
  def tick args
    # ./samples/07_advanced_rendering/12_blend_modes_additive_modulo/app/main.rb
    # Sample app shows how to use blend modes to create a masking layer
    # Special thanks to akzidenz@discord (https://akzidenz.itch.io/) for providing this sample app
    #
    # blendmode reference:
    #  1: alpha blending (default)
    #  2: additive blending
    #  4: modulo blending
    #  8: multiply blending
    # create a render target to represent the masking layer
    args.outputs[:mask].w = 1280
    args.outputs[:mask].h = 720

    speed = 2 # degrees per tick

    angle = Kernel.tick_count * speed

    args.outputs[:mask].sprites << {
      x: 0, y: 0, w: 1280, h: 720,
      path: :solid,
      r: 0, g: 0, b: 0 # <-- important (black color)
    }

    args.outputs[:mask].sprites << {
      x: Grid.w / 2,
      y: Grid.h / 2,
      w: 240, h: 240,
      anchor_x: 0.5,
      anchor_y: 0.5,
      path: :solid, # use a proper mask if you want to rotate anything other than a square.
      r: 255,
      g: 255,
      b: 255,
      a: 255,
      angle: angle,
      blendmode: 2,             # <-- important (2 means additive blending)
    }

    # render background to reveal
    args.outputs.sprites << { x: 0,
                              y: 0,
                              w: 1280,
                              h: 720,
                              path: 'sprites/bg.png' }

    # render masking layer over the bg to reveal
    args.outputs.sprites << {
      x: 0, y: 0, w: 1280, h: 720,
      path: :mask,
      blendmode: 4 # <-- important (4 means modulo blending)
    }
  end
end