Treasure Hunt IV

Review — where we got to 5 min

• <<> or <>> said yes for either snake.
• <not <touching [Hole v]?>> stopped digging twice.
• One watcher script ended the game, whoever took the last dig.
• The beep’s wait was the distance divided by 200.

Quick-fire

You press the green flag. Which of these should go back to its first value?

• digs left
• time
• best time

Today’s Topic 3 min

• (timer) and reset timer — Scratch’s own stopwatch
• Three chests in one round
• A best time the flag never resets, checked with <<> or <>>
• A start screen: a title, a START button, and one broadcast

Learning outcome

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

1. Time a game with the timer.
2. Keep a record that only changes when it is beaten.
3. Start a game from a button instead of the green flag.

Learnt — the clock and the front door 28 min

1 · Scratch has a stopwatch

(timer) is a round Sensing block. It counts seconds, all by itself. reset timer puts it back to 0.

1. Open Sensing. Tick the box next to (timer).
2. Watch the Stage. The number climbs with lots of decimals.
3. Click reset timer. It jumps back to 0.
4. Untick it. We will show a tidy time variable instead.

The timer has decimals: 12.4836. (round ()) makes it 12.

when flag clicked
reset timer
forever
  set [time v] to (round (timer))
end
              

when flag clicked
forever
  go to [mouse-pointer v]
  if <<mouse down?> and <(distance to [Treasure v]) < (60)>> then
    broadcast [found v]
  end
end

when I receive [found v]
stop [other scripts in sprite v]
say (join [Found in ] (join (time) [ seconds!]))
              

2 · A best time that stays

Make a variable called best time. Here is the one rule: nothing under the green flag touches it.

It changes in one place only: when a game ends. And only in two cases:

• there is no best time yet (it is still 0), or
• this time is smaller than the best.

Two cases, either one is enough. That is an or.

when I receive [found v]
stop [other scripts in sprite v]
if <<(best time) = (0)> or <(time) < (best time)>> then
  set [best time v] to (time)
end
say (join [Best: ] (best time))
            

3 · Three chests in a row

One chest is quick. Three is a race. After each find, the chest counts itself and jumps somewhere new.

An open chest stays behind, as a trophy. It is a clone — made exactly like a hole. It comes from a new sprite, Open Chest, and goes to the Detector.

when flag clicked
hide
switch costume to [chest v]
go to x: (pick random (-180) to (200)) y: (pick random (-150) to (-40))

when I receive [found v]
change [treasures v] by (1)
start sound [Coin v]
create clone of [Open Chest v]
go to x: (pick random (-180) to (200)) y: (pick random (-150) to (-40))
              

when flag clicked
hide

when I start as a clone
go to [Detector v]
show
              

On the Detector, a watcher counts to three:

when flag clicked
forever
  if <mouse down?> then
    if <(distance to [Treasure v]) < (60)> then
      broadcast [found v]
    end
    wait until <not <mouse down?>>
  end
end
              

when flag clicked
set [treasures v] to (0)
wait until <(treasures) = (3)>
broadcast [win v]

when I receive [win v]
stop [other scripts in sprite v]
say [All three!]
              

4 · A start screen

A real game has a front door. The green flag only sets the scene:

• the title and the START button show;
• the detector hides.

Clicking START sends broadcast [start v]. Everything that plays now waits for that message instead of the flag.

when flag clicked
show

when this sprite clicked
broadcast [start v]

when I receive [start v]
hide
              

when flag clicked
hide

when I receive [start v]
show
forever
  go to [mouse-pointer v]
end
              

5 · One script runs the round

Last lesson, one watcher waited for the digs to run out. Now the round can end two ways: out of digs, or three chests found. One script watches both, and runs the clock while it waits.

when I receive [start v]
set [digs left v] to (10)
set [treasures v] to (0)
reset timer
repeat until <<(digs left) < (1)> or <(treasures) = (3)>>
  set [time v] to (round (timer))
end
if <(treasures) = (3)> then
  broadcast [win v]
else
  broadcast [lost v]
end
            

Basic — the finished hunt 24 min

Open your hunt from last lesson. This is the last big build. Play after every step.

Step 1 — new variables

1. Make treasures, time and best time, for all sprites.
2. Tick all three, and digs left, so they show.

Step 2 — the Open Chest

1. Duplicate the Treasure. Rename the copy Open Chest. Delete its shut costume and all its scripts.
2. Give it the Hole’s two stacks: hide at the flag, and the clone script.

Step 3 — the Treasure moves on

1. Change the Treasure’s “found” script: count, Coin, clone of Open Chest, new random spot.
2. Change its when flag clicked to when I receive [start v].

Step 4 — the title and START

1. Paint a Title sprite with the game’s name. Paint a Start button. Or use Button2.
2. Give both their stacks from section 4.

Step 5 — the Detector waits for START

1. Add when flag clicked and hide.
2. In every other script, swap when flag clicked for when I receive [start v].
3. Add show to the top of the follow script.
4. Add wait until <not <mouse down?>> to the top of the dig script.

Step 6 — the round, and the win

1. Delete last lesson’s watcher. Build the round script instead.
2. Change the “found” script on the Detector into a “win” script, as below.
3. Win once. Press the flag. Win again, slower. The best time must not change.

The whole Detector

when flag clicked
hide

when I receive [start v]
show
forever
  go to [mouse-pointer v]
  if <(distance to [Treasure v]) < (60)> then
    say [Hot!]
  end
  if <<(distance to [Treasure v]) > (60)> and <(distance to [Treasure v]) < (150)>> then
    say [Warm]
  end
  if <(distance to [Treasure v]) > (150)> then
    say [Cold]
  end
end

when I receive [start v]
wait until <not <mouse down?>>
forever
  if <mouse down?> then
    if <not <touching [Hole v]?>> then
      if <(distance to [Treasure v]) < (60)> then
        broadcast [found v]
      else
        change [digs left v] by (-1)
        create clone of [Hole v]
      end
    end
    wait until <not <mouse down?>>
  end
end

when I receive [start v]
forever
  if <<touching [Snake v]?> or <touching [Snake2 v]?>> then
    change [digs left v] by (-1)
    start sound [Bonk v]
    wait (1) seconds
  end
end

when I receive [start v]
forever
  start sound [Computer Beep v]
  wait ((distance to [Treasure v]) / (200)) seconds
end

when I receive [win v]
stop [other scripts in sprite v]
if <<(best time) = (0)> or <(time) < (best time)>> then
  set [best time v] to (time)
end
say (join [All three in ] (join (time) [ seconds!]))

when I receive [lost v]
stop [other scripts in sprite v]
say [Out of digs!]
            

The record to beat

Show the best time on the start screen, so there is something to aim at.

• Before any game, the title says No best time yet.
• After a win, it says Best time: and the number.
• It hides with the title when the game starts.

when flag clicked
show
if <(best time) = (0)> then
  say [No best time yet]
else
  say (join [Best time: ] (best time))
end
            

Play again

Right now, a second game needs the green flag. Close the loop without it.

• Three seconds after a win or a loss, the title and START come back.
• Clicking START begins a fresh round.
• The old holes and open chests are gone.
• The best time stays.

when I receive [win v]
wait (3) seconds
show

when I receive [lost v]
wait (3) seconds
show
            

when I receive [start v]
delete this clone
            

Medals

A time is a number. A medal is a reward. Give one out.

• Under 20 seconds wins gold.
• Under 40 seconds wins silver.
• Anything slower wins bronze.
• The detector says the time first, then the medal.

when I receive [win v]
stop [other scripts in sprite v]
if <<(best time) = (0)> or <(time) < (best time)>> then
  set [best time v] to (time)
end
say (join [All three in ] (join (time) [ seconds!])) for (2) seconds
if <(time) < (20)> then
  say [Gold medal!]
else
  if <(time) < (40)> then
    say [Silver medal!]
  else
    say [Bronze medal!]
  end
end
            

A shrinking Hot zone

Make each chest harder than the last.

• The first chest counts as found within 60 steps.
• Every chest you find makes that 15 steps smaller.
• The words and the dig both use the new size.

change [hot size v] by (-15)
            

if <(distance to [Treasure v]) < (hot size)> then
  say [Hot!]
end
if <<(distance to [Treasure v]) > (hot size)> and <(distance to [Treasure v]) < (150)>> then
  say [Warm]
end
            

Summary 5 min

• (timer) counts seconds by itself. reset timer puts it back to 0.
• A record changes only when it is beaten. Keep it away from the green flag.
• <<(best time) = (0)> or <(time) < (best time)>> covers the first game and every faster one.
• A clone hears broadcasts too. Leave trophies from a separate sprite.
• A start screen is one broadcast. The flag sets the scene; START begins the game.

Timer

Scratch’s stopwatch. It counts seconds on its own.

Record

The best result so far. Only a better one replaces it.

Start screen

What the player sees before the game begins.

Round

One game, from START to a win or a loss.

The Treasure Hunt, finished

Four lessons ago the detector could only say Hot! or Cold. Since then you have used:

• <() < ()>, <() > ()> and <() = ()> to compare;
• and, or and not to build bigger questions;
• if / then and if / then / else to choose;
• (distance to [Treasure v]), the mouse and the timer to sense the world.

Hand in

Share your finished hunt and send the link to your teacher. Next lesson starts a new game: a robot that follows a line.