Castle Climb III

Review — Castle Climb II 5 min

• Each level is a save code in the levels list. unpack code :: custom cuts it into the level list.
• find start :: custom scans for the S and keeps its centre.
• E loads the next level; ^ sends the knight back to the start.

Quick-fire

The knight walks into column 6, row 11. If that cell were a checkpoint, what would start x and start y become?

Today’s Topic 3 min

• A map that changes while the game is running
• clear tile :: custom — rebuild one row with a dot in it
• Coins * and a key K you collect; a door D that opens with a key
• A checkpoint C that moves where you come back

Learning outcome

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

1. Change one letter of a level while the game runs, and redraw the map.
2. Make tiles you collect, and a tile that is solid only some of the time.
3. Move the restart point when the player reaches a checkpoint.

Learnt — a map that changes 30 min

1 · Changing one letter

A coin you have taken must stop being a coin. In the list, its * becomes a .. You met this problem in Tile Maker III: Scratch has no block that changes one letter, so set tile built the row again. clear tile :: custom is the knight’s version. It always writes a dot, at the col and row that tile at (x) (y) :: custom just found — and it does not stamp, because only the Tile sprite stamps.

1. Start with an empty new row.
2. Go along the row, letter 1 to letter 16.
3. At the knight’s column, add a .. Everywhere else, add the letter that was there.
4. Put the new row back in the list, then ask Tile to draw again.

define clear tile
set [new row v] to []
set [i v] to (1)
repeat (16)
  if <(i) = (col)> then
    set [new row v] to (join (new row) [.])
  else
    set [new row v] to (join (new row) (letter (i) of (item (row) of [level v])))
  end
  change [i v] by (1)
end
replace item (row) of [level v] with (new row)
            

2 · Coins

pick up :: custom runs after the middle-of-the-knight check, so tile already holds the letter there.

define pick up
if <(tile) = [*]> then
  clear tile :: custom
  change [coins v] by (1)
  start sound [Coin v]
  broadcast [redraw v]
end
if <(tile) = [K]> then
  clear tile :: custom
  change [keys v] by (1)
  start sound [Collect v]
  broadcast [redraw v]
end
if <(tile) = [C]> then
  set [start x v] to ((-225) + ((30) * ((col) - (1))))
  set [start y v] to ((165) - ((30) * ((row) - (1))))
end
            

3 · Keys and doors

A door is a brick that can change its mind. It lives in corner (dx) (dy) :: custom, where the knight asks “am I in something solid?”

• No key: count it as a hit, the same as a brick.
• A key: clear the door, use up the key, and do not count a hit. The knight walks in.

define corner (dx) (dy)
tile at ((x position) + (dx)) ((y position) + (dy)) :: custom
if <(tile) = [#]> then
  change [hits v] by (1)
end
if <(tile) = [D]> then
  if <(keys) > (0)> then
    clear tile :: custom
    change [keys v] by (-1)
    broadcast [redraw v]
  else
    change [hits v] by (1)
  end
end
            

4 · Checkpoints

Spikes already send the knight to start x, start y. So a checkpoint only has to change those two numbers to its own centre.

Basic — the key level 25 min

Carry on from your three-floor climb. Today it plays one new level with everything in it.

#################..............##...*.*.*K.....##..########....##..............##...........##.##.....C.**.....##....######....##..............##.##.......######S...^^^.*.D..E#################

Step 1 — the level

1. Paste the code above into levels as item 1 (or make your own with a K, a D, some coins and a C).
2. Make variables for all sprites: coins, keys, new row.
3. Add the Coin and Collect sounds to the knight.

Step 2 — the new My Blocks

1. Make clear tile :: custom and pick up :: custom. Tick Run without screen refresh on both.
2. Add the door to corner (dx) (dy) :: custom.

Step 3 — join them up

1. In check tiles :: custom, call pick up :: custom straight after the middle check.
2. In start level :: custom, set keys to 0.
3. Under the green flag, set coins to 0.
4. Get the key off the top shelf and out through the door.

define check tiles
tile at (x position) ((y position) - (6)) :: custom
if <<(tile) = [^]> or <(y position) < (-170)>> then
  go to x: (start x) y: (start y)
  set [y velocity v] to (0)
end
tile at (x position) (y position) :: custom
pick up :: custom
if <(tile) = [E]> then
  next level :: custom
end
              

define start level
set [code v] to (item (level number) of [levels v])
unpack code :: custom
find start :: custom
go to x: (start x) y: (start y)
set [y velocity v] to (0)
set [keys v] to (0)
broadcast [redraw v]
              

Coins left

Show how many coins are still out there.

• A coins left monitor, counted from the level when it loads.
• It goes down by one for every coin taken.

define count coins
set [coins left v] to (0)
set [i v] to (1)
repeat (192)
  if <(letter (i) of (code)) = [*]> then
    change [coins left v] by (1)
  end
  change [i v] by (1)
end
            

A flag that turns gold

A checkpoint should show that it worked.

• Give the Tile sprite a costume called reached: the checkpoint tile with its flag painted gold.
• The checkpoint you reached is drawn gold. The others stay green.
• Do not change the letter: it stays C, so the save format still works.

set [letter v] to (letter (c) of (item (r) of [level v]))
if <<(letter) = [C]> and <<(c) = (flag col)> and <(r) = (flag row)>>> then
  switch costume to (reached v)
else
  switch costume to (letter)
end
            

A coin gate

Make the player collect everything before they can leave.

• While any coin is left, the exit does nothing.
• Standing in the exit with coins left, the knight says how many: 2 coins to go!
• With every coin taken, the exit works as before.

if <(tile) = [E]> then
  if <(coins left) > (0)> then
    say (join (coins left) [ coins to go!]) for (1) seconds
  else
    next level :: custom
  end
end
            

Keys that follow you

A number in a monitor is easy to miss. Show the keys the knight is carrying.

• Every key you carry trails behind the knight, in a line.
• Use a key on a door, and one fewer follows.
• Up to three keys.

when flag clicked
hide
set [place v] to (1)
repeat (3)
  create clone of [myself v]
  change [place v] by (1)
end

when I start as a clone
forever
  go to x: ((knight x) - ((16) * (place))) y: ((knight y) + (6))
  if <(keys) < (place)> then
    hide
  else
    show
  end
end
            

Summary 5 min

• To change one letter, build a new row and replace the old one.
• Change the list, then draw it again: the picture follows the list.
• A door is a brick only while you have no key.
• A checkpoint is two numbers: where the knight comes back.

Rewrite

Changing the level list while the game runs.

Redraw

Stamping the whole map again from the list.

Checkpoint

A place that becomes your new start once you reach it.

Collectable

A tile that is counted and removed when you touch it.

Hand in

Save your key level. Next lesson the climb gets lives, a moment when each floor is cleared, a title — and you ship the whole game.