Car Race Game III

Review — where we got to 5 min

• The key pushes a number; one move block does the moving.
• Speed × 0.9 every loop is friction, and it is what makes the car coast.
• Five checkpoint posts, in order, make a lap honest.

Quick-fire

Your car keeps 90% of its speed each loop. What if you changed that to 80%?

Today’s Topic 3 min

• Grass as friction, not as a wall
• ask () and wait — letting the player type
• A game with five pages
• Buttons as costumes, not as sprites

Learning outcome

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

1. Change how a car handles by changing one number.
2. Ask the player a question and keep the answer.
3. Build a menu from one sprite, and move between pages with broadcasts.

Learnt — friction and pages 28 min

Off the track, properly

Last week’s mission asked for a car that goes slower on the grass instead of being sent back to the start. You already have the block that does it — friction.

On the road you keep 90% of your speed each loop. On the grass, keep only 80%. That is the whole change.

if <touching color [#3FA34D]?> then
  set [speed v] to ((speed) * (0.8))
  set [steering v] to ((steering) * (0.7))
else
  set [speed v] to ((speed) * (0.9))
  set [steering v] to ((steering) * (0.85))
end
            

Letting the player type

In Sensing there is a block you have not used yet:

ask [How many laps to win?] and wait
set [laps to win v] to (answer)
            

There is only one answer. Ask a second question and the first reply is gone.

So copy it out straight away — into (laps to win), player name, whatever you need it for.

A game has pages

Big games are not one screen. Ours will have five:

1. Menu — 1 player, 2 players, Setting, How to Play
2. Game Mode — Time Race or Lap Race
3. Race Track — which track
4. Game Play — the race itself
5. Play Again — who won, and what next

Each page is a broadcast. Send it, and the game moves on.

The problem with buttons

In Level 1’s Lesson 10 you made buttons the obvious way: one sprite each. Four buttons, four sprites, four scripts. Fine.

Five pages of buttons is fifteen sprites, and fifteen scripts that are all nearly the same. You will lose track by the second page.

Buttons as costumes

Here is the better way, and it is the same idea as the checkpoints last week:

1. One sprite per page. Call it Menu.
2. One costume per button on that sprite, named after what it says.
3. A My Block that places one button and clones it.
4. Hide the real sprite. Only the clones are ever seen.

define Button (x) (y) (name) (size)
go to x: (x) y: (y)
switch costume to (name)
set size to (size) %
create clone of [myself v]
            

when flag clicked
hide
Button (0) (120) [Title] (90) :: custom
Button (0) (40) [1 Player] (80) :: custom
Button (0) (-20) [2 Players] (80) :: custom
Button (0) (-80) [Setting] (80) :: custom
Button (0) (-140) [How to Play] (80) :: custom
            

A clone finds out who it is

Every clone runs the same script, so every clone would broadcast the same thing. It has to ask its own costume which button it is:

if <<touching [mouse-pointer v]?> and <mouse down?>> then
  wait until <not <mouse down?>>
  if <(costume [name v]) = [1 Player]> then
    broadcast [Game Mode v]
  end
  if <(costume [name v]) = [Setting]> then
    broadcast [Setting v]
  end
end
            

Making it feel like a button

Dim every button, and undim the one the mouse is on:

forever
  if <touching [mouse-pointer v]?> then
    clear graphic effects
  else
    set [brightness v] effect to (-15)
  end
end
            

Two last fixes

The title lights up too. It is a costume on the same sprite, so it gets the same effect — and clicking it does nothing, which looks broken. Wrap the whole thing:

if <not <(costume [name v]) = [Title]>> then
end
            

Only the clicked button disappears. Each clone should leave when anybody makes a choice:

when I receive [Game Mode v]
delete this clone
            

Basic — build the menu page 24 min

Step 1 — the friction fix

In your race, wrap the two friction lines in an if / else on touching color [grass]?, with 0.8 and 0.7 in the grass half. Do it for both cars.

Step 2 — a new sprite called Menu

Paint your title as costume 1. Then paint one costume per button. Name each costume exactly what it says — you will be comparing against those names.

Step 3 — the Button block

Make a block with four inputs: x, y, name, size. Inside: go to, switch costume, set size, create clone.

Step 4 — place them

when flag clicked, hide, then one Button call per button.

Step 5 — the clone script

Show, go to front, then the forever loop: the hover effect, then the click check.

Step 6 — the two fixes

Wrap everything in the “not Title” check, and add a when I receive [Game Mode v] → delete this clone for each message.

Grass that costs you

• More friction off the track, for both speed and steering.
• Both cars, each with their own numbers.
• Nothing resets and nothing teleports.

One sprite, one menu

• A menu page built from a single sprite with one costume per button.
• Buttons light up under the mouse; the title does not.
• Clicking any button clears the whole page.
• Each button sends a different message.

All five pages

The deck’s mission.

• Menu, Game Mode, Race Track, Game Play, Play Again.
• Two game modes: Time Race and Lap Race.
• Two tracks to choose from.
• The choices go into variables, so Game Play knows what to show.

A Setting page that works

Your menu has a Setting button. Make it do something.

• Ask how many laps win the race, and use that number.
• Ask for each player’s name, and show it on the Play Again page.
• Ask how fast the cars should be.

Summary 5 min

• Off the track is more friction — a cost, not a punishment.
• ask () and wait fills one place called answer, and the next question wipes it.
• A game is a set of pages, and a broadcast moves you between them.
• A page’s buttons are costumes on one sprite, cloned by a My Block.
• A clone reads its own costume to find out what it is meant to do.

answer

Where Scratch puts whatever the player typed. There is only one.

Page

One screen of a game. Only one is ever showing.

Refactor

Changing how code is written without changing what it does.

Hover

The mouse being over something without clicking it.

Hand in

Share your project and send the link to your teacher. Next lesson is the last of the Car Race — the pages and the racing finally join up.