Boss Tower II

Review — Boss Tower I 5 min

• One phase variable, four values: idle, wind-up, attack, recover.
• The wind-up is the tell. The recover is the window.
• Each phase ends by naming the next one.

Quick-fire

The dragon’s attack is always one fireball, at the knight. After three fights, what does a player stop doing?

Today’s Topic 3 min

• A pattern list the boss steps through
• A move as a list of spots, shared by the warning and the fire
• Many fireballs at once, as clones
• A fair pattern: there is always a gap

Learning outcome

By the end of this lesson you will be able to:

1. Make a sprite step through a list, and start again at the end.
2. Turn one list into a row of clones, each in its own place.
3. Check an attack can always be dodged.

Learnt — moves from lists 28 min

1 · The pattern is a list

The dragon now knows three moves: fireball, rain and sweep. A list called pattern holds them in order. A variable called step says which one is next.

1. The wind-up reads (item (step) of [pattern v]).
2. The attack adds 1 to step.
3. When step runs past the end of the list, it goes back to 1.

when flag clicked
go to x: (0) y: (70)
set [step v] to (1)
set [phase v] to [idle]
forever
  if <(phase) = [idle]> then
    switch costume to [dragon-a v]
    glide (1.2) secs to x: (pick random (-150) to (150)) y: (70)
    set [phase v] to [wind-up]
  end
  if <(phase) = [wind-up]> then
    switch costume to [dragon-b v]
    plan (item (step) of [pattern v]) :: custom
    broadcast [warn v]
    wait (1) seconds
    set [phase v] to [attack]
  end
  if <(phase) = [attack]> then
    switch costume to [dragon-c v]
    broadcast [fire v]
    change [step v] by (1)
    if <(step) > (length of [pattern v])> then
      set [step v] to (1)
    end
    wait (1) seconds
    set [phase v] to [recover]
  end
  if <(phase) = [recover]> then
    switch costume to [dragon-a v]
    glide (0.4) secs to x: (x position) y: (0)
    wait (1.2) seconds
    glide (0.4) secs to x: (x position) y: (70)
    set [phase v] to [idle]
  end
end
            

2 · A move is a list of spots

Every move is just “fire falls at these x positions”. So a My Block called plan turns the move’s name into a second list, spots.

define plan (name)
set [move v] to (name)
delete all of [spots v]
if <(name) = [fireball]> then
  add (knight x) to [spots v]
end
if <(name) = [rain]> then
  set [gap v] to (pick random (1) to (5))
  set [lane v] to (1)
  repeat (5)
    if <not <(lane) = (gap)>> then
      add ((-270) + ((lane) * (90))) to [spots v]
    end
    change [lane v] by (1)
  end
end
if <(name) = [sweep]> then
  set [lane v] to (200)
  repeat (8)
    add (lane) to [spots v]
    change [lane v] by (-45)
  end
end
            

Now the Marker and the Fireball both read spots. One list, two readers — so the warning and the fire can never disagree.

when I receive [fire v]
set [i v] to (1)
repeat (length of [spots v])
  set [my x v] to (item (i) of [spots v])
  create clone of [myself v]
  change [i v] by (1)
  wait (0.08) seconds
end

when I start as a clone
go to x: (my x) y: (40)
show
repeat until <(y position) < (-150)>
  change y by (-8)
  if <touching [Knight v]?> then
    change [burns v] by (1)
    delete this clone
  end
end
delete this clone
              

when I receive [warn v]
set [i v] to (1)
repeat (length of [spots v])
  set [my x v] to (item (i) of [spots v])
  create clone of [myself v]
  change [i v] by (1)
end

when I start as a clone
go to x: (my x) y: (-150)
repeat (5)
  show
  wait (0.1) seconds
  hide
  wait (0.1) seconds
end
delete this clone
              

3 · Fair means a gap

A pattern is fair when a player who reads the warning can always get out. Rain with all five lanes burning is not hard. It is impossible.

Basic — the dragon with a pattern 25 min

Open your boss fight from last lesson.

Step 1 — the lists and variables

1. Make two lists for all sprites: pattern and spots.
2. Type fireball, rain and sweep into pattern, one per line.
3. Variables for all sprites: step, move and gap. On the Dragon only: lane.
4. On the Fireball and on the Marker, for that sprite only: my x and i.

Step 2 — the plan

1. On the Dragon, make a block called plan with one input, name. Tick Run without screen refresh.
2. Build the plan from Learnt section 2.

Step 3 — the brain

1. Add set [step v] to (1) under the green flag.
2. Rebuild the wind-up and the attack as in Learnt section 1.

Step 4 — fire and markers

1. Replace the Fireball’s clone script with the two from Learnt section 2. Keep hide on its green flag.
2. Do the same for the Marker.
3. Play. Watch the floor, and stand where it does not blink.

A new order

Change how the dragon fights without changing a single script.

• The dragon does: fireball, fireball, rain, sweep — then starts again.
• No script is touched. Only the list.

The slam

Teach the dragon a fourth move.

• slam: the dragon dives to the floor where the knight stood at the wind-up.
• If it lands on the knight, that is a burn.
• The floor blinks there first, like every other move.
• No fireballs fall during a slam.

if <(name) = [slam]> then
  add (knight x) to [spots v]
end
            

if <(move) = [slam]> then
  glide (0.25) secs to x: (item (1) of [spots v]) y: (-95)
  if <touching [Knight v]?> then
    change [burns v] by (1)
  end
  wait (0.3) seconds
  glide (0.4) secs to x: (x position) y: (70)
end
            

Random, but fair

A fixed order can be learnt by heart. Shuffle it — carefully.

• Each wind-up picks a random move from the pattern list.
• The same move never comes twice in a row.
• A history list on the Stage shows every move so far.

define pick next move
repeat until <not <(next) = (last)>>
  set [next v] to (item (pick random (1) to (length of [pattern v])) of [pattern v])
end
set [last v] to (next)
            

A ring of fire

Not every move falls straight down.

• A ring move: fireballs fly out from the dragon in every direction.
• One every 30 degrees — but two neighbours are missing, so there is a way through.
• The missing pair is different each time.

when I receive [ring v]
set [my dir v] to (0)
repeat (12)
  if <not <<(my dir) = (gap dir)> or <(my dir) = (((gap dir) + (30)) mod (360))>>> then
    create clone of [myself v]
  end
  change [my dir v] by (30)
end

when I start as a clone
go to x: (0) y: (40)
point in direction (my dir)
show
repeat (45)
  move (6) steps
end
delete this clone
            

Summary 5 min

• A pattern list and a step variable make a boss that follows a routine.
• A new order, or a new move in the list, needs no new script.
• A move is a list of spots. The warning and the fire both read it, so they always agree.
• A fair attack always leaves a gap a reading player can reach.

Pattern

The order a boss does its moves in.

Step

Which item of a list comes next.

Fair

Always beatable by a player who reads the warning.

Gap

The safe place an attack leaves on purpose.

Hand in

Save your boss fight. Next lesson the dragon gets a health bar drawn with the Pen — and at half health, it gets angry.