Jump Dash II

Review — where we got to 5 min

Last week you built a run: a hop, rocks crossing the Stage, and an ouch.

• The rock is a clone. It goes to x: 240, walks left, and deletes itself.
• The rock asks touching [Hare v]? inside its own loop.

Quick-fire

Which sprite should count the score — the runner, or the rock?

Today’s Topic 3 min

• A score that counts the rocks you cleared, not the seconds you survived
• Three lives, and a hit that costs exactly one of them
• if <(lives) = (0)> then as the end of a game
• Why the ending needs its own broadcast

Learning outcome

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

1. Add a point at the moment a rock is safely past.
2. Take one life for one hit, and no more than one.
3. End the game at zero and show the player their score.

Learnt — a score, three lives, a game over 27 min

1 · A point for getting past

A rock earns you a point by reaching the left edge in one piece. That is the line after the loop, and it is the only place it can go.

1. Make a variable called score. Tick its box so it shows on the Stage.
2. On the rock’s flag stack, add set [score v] to (0).
3. In the clone stack, after the repeat (60) and before the delete, add change [score v] by (1).
4. Play it. Every rock that goes by is worth one.

when I start as a clone
go to x: (240) y: (-125)
show
repeat (60)
  change x by (-8)
end
change [score v] by (1)
delete this clone
            

2 · Three lives

A life is a second variable. The rock takes one when it hits, then removes itself, so one rock can only ever cost you one.

1. Make a second variable called lives and show it too.
2. On the flag, set [lives v] to (3).
3. In the touching if, replace the ouch broadcast with change [lives v] by (-1).
4. Keep delete this clone right underneath it.
5. Play it. Get hit on purpose three times and watch the number fall.

repeat (60)
  change x by (-8)
  if <touching [Hare v]?> then
    start sound [Boing v]
    change [lives v] by (-1)
    delete this clone
  end
end
            

3 · What zero means

Zero lives is not a smaller number. It is the end. The rock notices it, and tells everybody with a broadcast.

1. Under change [lives v] by (-1), add if <(lives) = (0)> then.
2. Inside that if, broadcast [game over v].
3. On the hare, add a when I receive [game over v] stack.
4. Say the score, wait, then stop all.
5. Play a whole game until it ends by itself.

when I receive [game over v]
say (join [Game over. Rocks cleared: ] (score)) for (3) seconds
stop [all v]
            

Basic — build the scoring 25 min

Open last week’s project. Everything today is added to it.

Step 1 — the two variables

1. Make score and lives. Show both on the Stage.
2. Drag their monitors to a corner where the runner never goes.
3. Set both of them on the flag. Every game starts the same way.

Step 2 — scoring

1. Add the point after the clone’s loop.
2. Play for twenty seconds without hopping and check the number climbs.

Step 3 — losing a life

1. Change the touching if so it costs a life instead of ending the game.
2. Check the deleting still happens.
3. Take three hits on purpose. It should take exactly three.

Step 4 — the ending

1. Add the zero question and the broadcast.
2. Build the receiving stack on the runner.
3. Play three full games.

Step 5 — make it fair

1. Write down the score you got each time.
2. If every game ends under 5, the rocks are too fast or too close together.
3. If you never lose, they are too slow.

Not every rock is worth the same

A rock you barely have to move for should not pay as well as one that nearly gets you.

• Two sizes of obstacle, and you can tell them apart at a glance.
• The harder one is worth more.
• The score still starts at zero every game.

Make a hit feel like a hit

At the moment a life vanishes silently. A player looking at the runner misses it completely.

• Something happens to the runner that you can see.
• It lasts long enough to notice and short enough not to annoy.
• The runner goes back to normal afterwards.
• It works on the third hit as well as the first.

An ending worth reading

Right now the game ends with one line and a stop. Give the player a proper end of the run.

• It says how many rocks were cleared.
• It says something different for a good run and a bad one.
• It stays on screen long enough to be read out loud.
• It tells the player how to start again.

Lives you can count without reading

A number in the corner is fine. Three hearts that go out one at a time is a game. Build the second one.

• Three hearts on the Stage at the start of every game.
• One goes when a life goes, and the right one goes each time.
• They all come back when the flag is pressed.
• The lives variable can be hidden and the game still makes sense.

Summary 4 min

The same run as last week, and now it is a game you can be good at.

1. The rock scores the point, because only the rock knows it got past.
2. One hit costs one life, and the delete is what makes that true.
3. Zero lives is an ending, and it gets its own broadcast.
4. The last thing on the game-over stack is the stop, never the first.

Score

A count of what the player achieved. Set to 0 at the start of every game.

Lives

How many mistakes are left. One hit, one life.

Game over

The broadcast that ends the run and shows the score.

join

Glues words onto a number so a score reads as a sentence.

Next lesson: it speeds up, there is something worth collecting, and standing still stops working.