Jump Dash III

Review — where we got to 5 min

The run has a score and three lives. It ends by itself and tells you how you did.

• The clone scores by reaching the far edge, and costs a life by touching the runner.
• if <(lives) = (0)> then broadcasts the ending.

Quick-fire

The rock steps -8 every time round the loop. What would make it faster without touching the loop?

Today’s Topic 3 min

• A variable inside a motion block, so one number steers the whole game
• A game that gets harder the longer you last
• Something worth collecting, at a height only a hop reaches
• Something to avoid at that same height, so hopping has a cost

Learning outcome

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

1. Drop a variable into a motion block and change the game by changing it.
2. Reward a hop and punish a hop in the same game.
3. Say why a game that speeds up for ever stops being fun.

Learnt — speed, a star, and a bat 27 min

1 · One number that steers everything

The -8 in the rock’s loop is the whole difficulty of the game. Take it out and put a variable in its place.

1. Make a variable called speed.
2. On the rock’s flag stack, add set [speed v] to (-8).
3. In the clone stack, drag speed into the change x by ( ) block, on top of the −8.
4. In the factory loop, after the clone is made, add change [speed v] by (-0.2).
5. Play for two minutes. It should feel different at the end.

when flag clicked
hide
set [speed v] to (-8)
forever
  wait (1.6) seconds
  create clone of [myself v]
  change [speed v] by (-0.2)
end
            

2 · Something worth having

A star flies at hop height. You can only reach it in the air, so it turns a hop into a decision rather than a reflex.

1. Add the Star sprite. Set its size to 60.
2. Give it the same factory shape as the rock, with a longer wait.
3. In its clone stack, go to go to x: (240) y: (15).
4. Walk it left the same way the rock walks.
5. Inside that loop, ask touching [Hare v]? and pay 5 points.

when I start as a clone
go to x: (240) y: (15)
show
repeat (60)
  change x by (speed)
  if <touching [Hare v]?> then
    start sound [Collect v]
    change [score v] by (5)
    delete this clone
  end
end
delete this clone
            

3 · Something to avoid up there

If the air is always safe, the best player just stays in it. The bat flies at exactly hop height and makes that a bad plan.

1. Add the Bat sprite, size 50.
2. Copy the star’s scripts by dragging them onto the bat in the sprite list.
3. Open the bat and change what touching does: a life instead of five points.
4. Give it its own wait so bats and stars do not always arrive together.
5. Play it. Try surviving by hopping all the time and see how far you get.

when I start as a clone
go to x: (240) y: (10)
show
repeat (60)
  change x by (speed)
  next costume
  if <touching [Hare v]?> then
    start sound [Boing v]
    change [lives v] by (-1)
    delete this clone
  end
end
delete this clone
            

Basic — build all three 25 min

Open last week’s game. Test after every step, not at the end.

Step 1 — the speed variable

1. Make it, set it on the flag, and put it in the rock’s change x block.
2. Play. Nothing should have changed yet.
3. Add the change of −0.2 and play for two minutes.

Step 2 — the star

1. Add the sprite and build its factory.
2. Build the clone stack at hop height.
3. Check you cannot reach it standing still.

Step 3 — the bat

1. Drag the star’s scripts onto the bat.
2. Change the points into a life.
3. Change its wait so it does not follow the star exactly.
4. Add next costume so its wings move.

Step 4 — balance it

1. Play five games and write down each score.
2. If bats never catch you, they are too rare or too low.
3. If stars are never worth the risk, move them or pay more.

Step 5 — read your own game

1. Say out loud what a good player does. Then check your game rewards that.

A third thing at a third height

The ground says hop. Hop height says think. Add one more, and it must not do either of those jobs again.

• A new sprite at a height nothing else uses.
• It does something the other three do not.
• A player can tell what it does the first time they meet it.

Fast enough, and no faster

Leave the game running long enough and it becomes impossible for anybody. Find the point where it stops being fun, and stop it there.

• The game still gets harder as you last longer.
• It never gets faster than a person can react to.
• You can say what number you chose, and why that one.

Make the star a real choice

A star you can take for free is just a slow point. Make taking one cost the player something.

• Reaching a star sometimes puts you somewhere you did not want to be.
• Ignoring stars is a real way to play, and a safe one.
• Taking every star is possible, but only if you are good.

Warn me before it arrives

At high speed a bat crosses the Stage before your hand moves. That is not difficulty, it is luck. Give the player half a second of warning.

• Something tells the player what is coming before it is on screen.
• The warning is at the right height for the thing that follows.
• It disappears once the thing arrives.
• The game is measurably easier with it than without.

Summary 4 min

Three things arrive now, and the player has to tell them apart in half a second.

1. A variable in a motion block steers every clone at once.
2. A game that speeds up needs a limit, or it plays itself into nonsense.
3. A reward at hop height makes hopping a decision.
4. A danger at hop height makes it a risky one.

speed

One variable that every obstacle reads. Change it and the whole game changes.

Clamp

Stopping a number going past a limit, however long the game runs.

Reward

Something worth points, placed where it is not free.

Lane

A height. Each one asks the player a different question.

Next lesson: a title screen, a start button, and a best score that survives the game ending.