Brick Breaker III

Review — Brick Breaker II 5 min

• The wall was a list. Each letter was a brick, and the letter was its hit points.
• Brick clones only remembered my col and my row, and drew what the list said.
• The ball moved across and asked brick at (x) (y) :: custom, then moved up and asked again — so it knew which face it hit.

Quick-fire

In your Brick Breaker II game, the ball starts with vx 4 and vy 5. After a wall, a brick and the paddle, what could vx be?

Today’s Topic 3 min

• The offset: where the ball lands on the paddle
• vx from the offset — aiming
• A speed that grows, and two caps that keep it fair
• A miss that puts the speed back

Learning outcome

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

1. Work out vx from where the ball hits the paddle.
2. Make a game harder over time, with a cap that keeps it possible.
3. Explain why a game is fair or unfair with a number.

Learnt — aiming with the paddle 28 min

1 · One slant for ever

Flipping only changes the sign. So the ball’s slant never changes. It lands in different places, but it always leaves at the same angle.

2 · The offset sets vx

Every real paddle game cheats a little. It does not bounce like a mirror. Instead, the spot the ball lands on decides where it goes.

1. The offset is ((x position) - (paddle x)): how far from the middle the ball landed.
2. The paddle is 88 wide, so the offset runs from −44 (far left) to 44 (far right).
3. ((offset) / (44)) turns that into a number from −1 to 1.
4. Times speed, it is the new vx. And vy is just speed, going up.

if <<touching [Paddle v]?> and <(vy) < (0)>> then
  set [offset v] to ((x position) - (paddle x))
  set [vx v] to (((offset) / (44)) * (speed))
  set [vy v] to (speed)
end
            

3 · Faster, but fair

A game should get harder. So every paddle hit adds 0.5 to speed. But the paddle can only move 8 steps a frame. A ball faster than that cannot always be caught — that is not hard, it is unfair.

Two caps keep it fair:

if <<touching [Paddle v]?> and <(vy) < (0)>> then
  set [offset v] to ((x position) - (paddle x))
  if <(offset) > (44)> then
    set [offset v] to (44)
  end
  if <(offset) < (-44)> then
    set [offset v] to (-44)
  end
  set [vx v] to (((offset) / (44)) * (speed))
  set [vy v] to (speed)
  change [hits v] by (1)
  if <(speed) < (8)> then
    change [speed v] by (0.5)
  end
end
            

Below, a robot paddle that moves at most 8 a frame plays under a steel roof. The only difference between the two is the speed cap.

4 · A fair miss

After a miss, the speed goes back to 5. Otherwise the player serves straight into the fastest ball of the game. serve now sends the ball straight up at the current speed.

define serve
repeat (15)
  go to x: (paddle x) y: (-128)
end
set [vx v] to (0)
set [vy v] to (speed)
              

if <(y position) < (-170)> then
  change [lives v] by (-1)
  if <(lives) = (0)> then
    say [Game over!]
    stop [this script v]
  end
  set [speed v] to (5)
  serve :: custom
end
              

Basic — an aiming paddle 25 min

Open your Brick Breaker II project. The wall, the bricks and the four My Blocks stay.

Step 1 — three new variables

1. Make speed, offset and hits for all sprites. Tick speed so it shows.
2. Change serve to the straight-up version in Learnt section 4.

Step 2 — the new main loop

when flag clicked
set [lives v] to (3)
set [score v] to (0)
set [speed v] to (5)
serve :: custom
forever
  move ball :: custom
  walls :: custom
  if <<touching [Paddle v]?> and <(vy) < (0)>> then
    set [offset v] to ((x position) - (paddle x))
    if <(offset) > (44)> then
      set [offset v] to (44)
    end
    if <(offset) < (-44)> then
      set [offset v] to (-44)
    end
    set [vx v] to (((offset) / (44)) * (speed))
    set [vy v] to (speed)
    change [hits v] by (1)
    if <(speed) < (8)> then
      change [speed v] by (0.5)
    end
  end
  if <(y position) < (-170)> then
    change [lives v] by (-1)
    if <(lives) = (0)> then
      say [Game over!]
      stop [this script v]
    end
    set [speed v] to (5)
    serve :: custom
  end
end
            

Three hearts

A number in a box is hard to notice mid-game. Show lives as hearts.

• Three hearts sit in the top-left corner.
• Each miss fades one heart away, from the right.
• Hide the lives monitor.

when flag clicked
hide
set [my life v] to (1)
go to x: (-215) y: (160)
repeat (3)
  create clone of [myself v]
  change x by (30)
  change [my life v] by (1)
end

when I start as a clone
show
wait until <(lives) < (my life)>
repeat (8)
  change [ghost v] effect by (12)
  change y by (2)
end
delete this clone
            

Aim the serve

Every serve goes straight up. Let the player aim it with the same sum.

• While the ball waits, ← and → slide it along the paddle.
• It cannot slide off: it stays within 40 of the middle.
• Space serves it, using the paddle’s aiming sum.

define serve
set [offset v] to (0)
repeat until <key (space v) pressed?>
  if <<key (right arrow v) pressed?> and <(offset) < (40)>> then
    change [offset v] by (2)
  end
  if <<key (left arrow v) pressed?> and <(offset) > (-40)>> then
    change [offset v] by (-2)
  end
  go to x: ((paddle x) + (offset)) y: (-128)
end
set [vx v] to (((offset) / (44)) * (speed))
set [vy v] to (speed)
            

Spin

In real paddle games, a moving paddle drags the ball with it. Add that.

• The paddle moves with ← and → (8 a frame).
• pv is how far the paddle moved this frame.
• A hit adds 0.4 × pv to vx.

when flag clicked
go to x: (-30) y: (-150)
set [last x v] to (-30)
forever
  if <key (right arrow v) pressed?> then
    change x by (8)
  end
  if <key (left arrow v) pressed?> then
    change x by (-8)
  end
  set [pv v] to ((x position) - (last x))
  set [last x v] to (x position)
  set [paddle x v] to (x position)
end
            

change [vx v] by ((pv) * (0.4))
            

An autopilot

Make a paddle that plays by itself — not by chasing the ball, but by working out where it will land.

• While the ball comes down, the paddle works out where it will reach y −128.
• It counts the side walls on the way.
• It moves there at most 6 a frame, like a player would.

define predict
set [px v] to (ball x)
set [py v] to (ball y)
set [pvx v] to (vx)
set [pvy v] to (vy)
repeat until <(py) < (-128)>
  change [px v] by (pvx)
  change [py v] by (pvy)
  if <(px) > (232)> then
    set [pvx v] to ((0) - (pvx))
  end
  if <(px) < (-232)> then
    set [pvx v] to ((0) - (pvx))
  end
end
set [target v] to ((px) + (15))

when flag clicked
go to x: (0) y: (-150)
set [target v] to (0)
forever
  if <(vy) < (0)> then
    predict :: custom
  end
  set [gap v] to ((target) - (x position))
  if <(gap) > (6)> then
    set [gap v] to (6)
  end
  if <(gap) < (-6)> then
    set [gap v] to (-6)
  end
  change x by (gap)
  set [paddle x v] to (x position)
end
            

Summary 5 min

• Flipping keeps one slant for ever. The paddle aims by setting vx from the offset.
• (((offset) / (44)) * (speed)) turns a landing spot into a direction.
• The speed grows each hit, and a cap stops it outrunning the paddle.
• A miss puts the speed back to 5, so a serve is never the fastest ball.

Offset

How far from the middle something is: here, ball x minus paddle x.

Cap

The most a number is allowed to be.

Fair

Hard, but always possible for a player who plays well.

Hand in

Save your aiming game. Next lesson is the last of the arc: power-ups, many balls, sparks, levels — and a game you can win.