Jump Dash IV

Review — where we got to 5 min

Three lessons in, the game has everything except a way to meet it.

• Rocks on the ground, bats and stars at hop height, and a speed that climbs.
• A score, three lives, and a game over broadcast.

Quick-fire

The Quiz Show had a start button too. What did pressing the green flag do in that project?

Today’s Topic 3 min

• A title screen, and a game that does not start until it is asked to
• Moving scripts from when flag clicked to when I receive [play v]
• A best score that is not reset by the flag
• Ending a game back where it started, so there is always another go

Learning outcome

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

1. Start a game from a button instead of the green flag.
2. Keep a best score across games in one sitting.
3. Come back to your project cold and use it with nothing but the Stage to go on.

Learnt — a title, a best, and a way back in 27 min

1 · The flag stops starting the game

Every game script currently begins on the flag. They all move to a message, and the flag is left with one job: show the title.

1. Add a Button2 sprite in the middle-right. Name it Play.
2. Give it when this sprite clicked and broadcast [play v], then hide.
3. On every other sprite, swap when flag clicked for when I receive [play v].
4. Give the runner one flag stack that only sets up the title: show, go to the middle, say the name of the game.
5. Press the flag. Nothing should move until you click the button.

when this sprite clicked
start sound [Pop v]
hide
broadcast [play v]
            

2 · A number the flag must not touch

score belongs to one game. best belongs to all of them, so it is the one variable that is never set on the flag.

1. Make a variable called best and show it.
2. Do not put set [best v] to (0) anywhere.
3. On the game-over stack, ask if <(score) > (best)> then.
4. Inside it, set [best v] to (score) and say something loud.
5. Play three games and watch what best does after a bad one.

when I receive [game over v]
if <(score) > (best)> then
  set [best v] to (score)
  start sound [Cheer v]
  say (join [New best: ] (best)) for (3) seconds
else
  say (join [You cleared ] (score)) for (3) seconds
end
            

3 · Ending where you started

The last thing a game over does is put the title back. Then the whole thing can be played again without anybody hunting for the flag.

1. On the button, add when I receive [game over v].
2. Wait three seconds, then show.
3. On the game-over stack, take out stop [all v] and replace it with a broadcast the obstacles listen for.
4. On every factory, add a when I receive [stop game v] stack with stop [other scripts in sprite v] and hide.
5. Play, lose, and play again without touching the flag.

when I receive [stop game v]
stop [other scripts in sprite v]
hide
delete this clone
            

Basic — build the front door 25 min

This is the fiddliest build of the arc. Work sprite by sprite and test after each one.

Step 1 — the button

1. Add it, name it, and place it where nothing else goes.
2. Give it the clicked stack with the broadcast.
3. Give it a flag stack that shows it and puts it in place.

Step 2 — move every script over

1. Open each sprite in turn.
2. Swap the flag hat for the receive hat on every game script.
3. Press the flag and check the Stage stays still.

Step 3 — the title screen

1. Give the runner a flag stack: show, go to the middle, say the game’s name.
2. Make sure the obstacles are hidden until play starts.

Step 4 — the best score

1. Make the variable and leave it alone on the flag.
2. Build the if / else on the game-over stack.
3. Play three games, including a deliberately bad one.

Step 5 — play again

1. Bring the button back at the end of a game.
2. Stop and hide every obstacle when the game ends.
3. Play four games in a row without the flag.

A title screen worth looking at

The first screen is the only one everybody sees. Make yours say what it needs to.

• The name of the game, big enough to read.
• One obvious thing to click.
• Nothing moving that is not meant to be.

A best score that never goes down

Prove your best score works, in the one way that counts: by trying to break it on purpose.

• A good game, then a terrible one, then a middling one.
• The best is right after all three.
• Pressing the flag between games does not change it.

The cold test

You cannot see your own game properly while you still remember building it. Put time between you and it, then come back as a stranger would.

1. Save it and close the project.
2. Do something else for at least ten minutes.
3. Open it again with every script window shut, so only the Stage shows.
4. Play two whole games, following only what is on the screen.
5. Write down every moment you had to stop and think.

• You start it without opening a script.
• You work out the controls from the screen alone.
• You know the moment you have lost.
• You play a second game without hunting for the flag.

How to play

Add a second door to your title screen: a page that explains the game, and a way back from it.

• A second button on the title screen.
• A screen that explains the controls and the scoring.
• A way back to the title that always works.
• You cannot get stuck on any screen.

Summary 4 min

Jump Dash is finished, and it is the first game in the course with a front door.

1. The flag builds the title. A button starts the game.
2. Every game script listens for a message instead of the flag.
3. A best score is the one variable the flag must not touch.
4. A game that ends back at its title never needs the flag twice.

Title screen

The first screen. A name, a picture, and one thing to press.

Best

The highest score so far. Survives a game ending; does not survive closing Scratch.

Screen

A broadcast, and a set of sprites that show or hide when it arrives.

Stranger test

Watching somebody play with no help, and writing down where they stop.

Next lesson: a new arc — a ball that never stops moving, and a paddle that has to be in the right place.