Pet Pal III

Review — where we got to 5 min

Your pet has food, a bowl, a mood, an ending and a record. Two ideas carry today.

• The clock loop: a wait and a change block inside a forever.
• The mood script: an if that reads a variable and picks a costume.

Quick-fire

One need means the whole game is “click the bowl before the number runs out”. What does a second need add?

Today’s Topic 3 min

• Three needs, three buttons, three clocks at three speeds
• A mood that comes from the worst of the three
• Why three ifs in a row beats one if / else here
• A pet that paces when it is happy and stops when it is not

Learning outcome

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

1. Run several variables at once, each on its own clock.
2. Choose a costume by checking several variables in turn.
3. Make a sprite’s movement depend on a variable rather than on a key.

Learnt — three needs and one face 28 min

1 · The same clock, three times

You already have one. Two more are copies of it with different names and different waits.

1. Make two more variables: fun and sleep.
2. Right-click your food clock and choose Duplicate. Twice.
3. Change the variable in each copy using its dropdown.
4. Give each one a different wait: 1.1, 1.7 and 2.3 seconds.
5. Press the flag and watch all three fall at once.

when flag clicked
set [fun v] to (10)
forever
  wait (1.7) seconds
  change [fun v] by (-1)
end
            

Each need gets its own button, and each button is three blocks.

when this sprite clicked
start sound [Boing v]
change [fun v] by (4)
            

2 · One face, three questions

The pet has one face and three things that can be wrong with it. The trick is to start happy and let any of the three spoil it.

when flag clicked
forever
  switch costume to [dog2-a v]
  if <(food) < (4)> then
    switch costume to [dog2-c v]
  end
  if <(fun) < (4)> then
    switch costume to [dog2-c v]
  end
  if <(sleep) < (4)> then
    switch costume to [dog2-c v]
  end
end
            

Why not an if / else?

1. An if / else has two answers, and here there are three ways to be sad.
2. Nesting three if / elses inside each other is nine blocks deep and unreadable.
3. Setting happy first and then testing three times is flat, short, and easy to add a fourth need to.

3 · A happy pet moves

The last thing that makes this feel alive costs one if. A pet with enough fun paces up and down. A bored pet sits still.

1. On the pet’s green-flag stack, add set rotation style [left-right v].
2. Add another green-flag stack with a forever loop in it.
3. Inside the loop, put if <(fun) > (4)> then.
4. Inside THAT, two glide blocks: one to the right, one back.
5. Play it and stop feeding the ball. The pacing stops on its own.

when flag clicked
forever
  if <(fun) > (4)> then
    glide (1.5) secs to x: (120) y: (-30)
    glide (1.5) secs to x: (-120) y: (-30)
  end
end
            

Basic — build all three 25 min

Add one need completely, test it, then add the next. Never two at once.

Step 1 — the second need

1. Make a variable called fun.
2. Duplicate the food clock and change both dropdowns in the copy.
3. Give it a different wait time.
4. Add a Ball sprite, put it beside the bowl, and give it the three-block clicked stack.
5. Play for a minute with two needs.

Step 2 — the third

1. Do the same again for sleep.
2. Its button can be any sprite — a bed, a moon, a plain button.
3. Give it the slowest clock of the three.

Step 3 — the mood

1. Open your old mood script. It only knows about food.
2. Change it so it sets the happy costume FIRST, inside the loop.
3. Then add three ifs, one per need.
4. Test by letting each need run out on its own.

Step 4 — the pacing

1. Add set rotation style [left-right v] to the green-flag stack.
2. Add the pacing stack.
3. Play, and watch the pet stop when it gets bored.

Step 5 — tune the three speeds

1. Play a whole game and see which need you had to deal with most.
2. Slow that one down.
3. Play again. Repeat until no single button is the answer to everything.

Three buttons anybody can read

Anybody sitting down at your game should know what all three buttons do without asking — and that includes you, a week from now.

• Each button looks like the thing it does.
• Each one makes its own sound.
• They are lined up somewhere they will not be clicked by accident.

Say what is wrong

A sad face does not say which need is low. Make the pet ask for the thing it actually wants.

• Each need has its own sentence.
• The pet asks for whichever one is lowest, not for all three at once.
• It says nothing at all when everything is fine.

if <(food) < (fun)> then
  say [I am hungry.] for (1.5) seconds
else
  say [Play with me!] for (1.5) seconds
end
            

Make it a fair fight

Three needs should each matter. Tune the speeds until no single button is the answer to everything.

• The three clocks all run at different speeds.
• Over a whole game you press all three buttons roughly as often as each other.
• You can say which one you slowed down and why.
• You can survive two minutes, but only by concentrating.

A pet that sleeps

Clicking the bed should put the pet to sleep for a while. It stops getting hungry, it stops pacing, and none of the other buttons work — but sleep goes up fast.

• Sleeping is visible: a costume, a thought bubble, or both.
• Food and fun stop falling while the pet is asleep.
• The bowl and the ball do nothing while it sleeps.
• It wakes up on its own, without being clicked.

when this sprite clicked
set [asleep v] to (1)
change [sleep v] by (6)
wait (5) seconds
set [asleep v] to (0)
            

forever
  wait (1.1) seconds
  if <(asleep) = (0)> then
    change [food v] by (-1)
  end
end
            

Summary 4 min

One need was a chore. Three needs at three speeds is a game with decisions in it.

1. Each need is a variable, a clock and a button. Three copies of one shape.
2. Different speeds are what make the player choose.
3. Set the happy costume first, then let three ifs spoil it.
4. Movement can be decided by a variable instead of by a key.

Need

A variable the player has to keep up. This game has three.

Mood

A costume decided by looking at every need in turn.

Rotation style

Whether a sprite turns, flips, or stays upright when it changes direction.

Balance

Setting the speeds so every button matters as much as the others.

Next lesson: the pet gets a name you choose, a front page, and an ending that says how you did.