Shooting Game III

Review — where we got to 5 min

• Friction and push are named settings, so the feel is one number away.
• (hp) is “for this sprite only”, so every clone has its own health.
• Three hearts, and a referee that ends the game at zero.

Quick-fire

What actually makes a machine gun different from a pistol?

Today’s Topic 3 min

• Ammo, and running out of it
• Reloading, and a variable that means “busy”
• Four weapons from one My Block
• Each weapon remembering its own ammo

Learning outcome

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

1. Stop the player firing when a condition says they may not.
2. Load a whole set of settings with one custom block.
3. Save a value before overwriting it, and put it back later.

Learnt — an arsenal 28 min

A weapon is a row of numbers

Here are our four. Look across the rows, not down them:

The machine gun fires nearly three times a second — and takes three whole seconds to reload. The RPG takes six health off in one hit — and holds five shots. That is what makes choosing a weapon interesting.

Ammo

wait until <mouse down?>
if <<(ammo) > (0)> and <(reloading?) = (0)>> then
  create clone of [Bullet v]
  change [ammo v] by (-1)
  wait (fire rate) seconds
else
  wait (0.1) seconds
end
            

A variable that means “busy”

(reloading?) is not a score and not a setting. It holds 1 for busy and 0 for ready, and it is there so that two different scripts can agree about what the player is doing.

when [r v] key pressed
if <(reloading?) = (0)> then
  set [reloading? v] to (1)
  wait (reload speed) seconds
  set [ammo v] to (max ammo)
  set [reloading? v] to (0)
end
            

Four weapons, one block

Picking up a weapon means setting seven things at once. Doing that four times, in four places, is exactly what a My Block is for:

define Equip (slot)
if <(slot) = (1)> then
  set [weapon v] to [Pistol]
  set [bullet costume v] to [bullet1]
  set [damage v] to (1)
  set [fire rate v] to (0.35)
  set [bullet speed v] to (12)
  set [reload speed v] to (1.5)
  set [max ammo v] to (30)
  set [ammo v] to (ammo - Pistol)
end
            

Then the keys are three blocks each:

when [3 v] key pressed
Save ammo :: custom
Equip (3) :: custom
            

Save before you overwrite

Equip () :: custom writes over (ammo). So whatever was left in the gun you are putting down has to be stored first:

define Save ammo
if <(weapon) = [Pistol]> then
  set [ammo - Pistol v] to (ammo)
end
if <(weapon) = [Machine Gun]> then
  set [ammo - Machine Gun v] to (ammo)
end
            

One bullet, four jobs

The bullet sprite never learns anything about weapons. It just reads three variables when it is born:

when I start as a clone
go to [Human v]
point towards [mouse-pointer v]
switch costume to (bullet costume)
show
repeat until <touching [edge v]?>
  move (bullet speed) steps
end
            

Basic — build the arsenal 24 min

Step 1 — the settings

Seven variables: weapon, damage, fire rate, bullet speed, bullet costume, reload speed, max ammo. Plus (ammo), (reloading?) and (slot).

Step 2 — the four ammo stores

(ammo - Pistol), (ammo - Shotgun), and two more. Set each to its full amount at the start.

Step 3 — Equip

Make the block, one input, four ifs. Test with just slot 1 before writing the rest.

Step 4 — Save ammo

The second block, four ifs, no inputs.

Step 5 — the keys

1, 2, 3, 4, then Q, then R.

Step 6 — firing

Rewrite the fire loop with the two conditions and the fire-rate wait.

Step 7 — the bullet

Three costumes, and switch costume to (bullet costume) when the clone starts.

Ammo and reloading

• Every shot costs one bullet.
• At zero, clicking does nothing.
• R reloads, and takes time.
• You cannot fire while reloading, and R during a reload does nothing.

Four weapons

• 1, 2, 3, 4 pick a weapon; Q moves to the next.
• Each weapon has its own fire rate and reload time.
• Each weapon remembers its own ammo.
• The bullet looks different for each one.

They hit differently

The deck’s mission. Make the choice of weapon actually matter.

• Damage comes from the weapon, not from the bullet.
• Bullet speed comes from the weapon too.
• A big zombie takes one RPG or six pistol shots.
• Every weapon is worth using at some moment.

A readout worth looking at

Four ammo variables on the Stage is four grey boxes, three of which are wrong for the gun in your hands. Fix it.

• One readout, showing the weapon you are actually holding.
• Its ammo, and how many it holds — “11 / 15”.
• Something obvious when you are reloading.
• No grey monitors anywhere.

Summary 5 min

• A weapon is a set of numbers. The drawing is the least of it.
• A variable can be a state: (reloading?) holds 1 for busy, and two scripts agree because of it.
• A My Block with one input can set seven things at once — that is what makes four weapons manageable.
• Save the old value before you overwrite it, or the switch quietly loses it.
• One sprite can do four jobs if the differences live in variables.

Ammo

How many shots are left before reloading.

Fire rate

How long the game waits between shots.

State

A variable that says what is happening right now, like busy or ready.

Balancing

Changing numbers until every choice is worth making.

Hand in

Share your game and send the link to your teacher. Next lesson is the last one — coins, waves, and a shop.