Sketch Pad III — Scratch L4 Lesson 3

Learnt28 min · rainbow colour, a white eraser, stamp, a tool variable
Basic25 min · three tools on 1, 2 and 3
Challenge 1–327 min · say the tool, a stamp tool, a spray can
Extrabonus · a straight-line tool

WHAT IT SHOULD LOOK LIKE

One pencil, three tools. A number key picks the tool; the tool decides what a drag does.

key 2, then drag

Review — Sketch Pad II 5 min

set pen color to [#D400AB] and set pen size to (8) change the next line.
Every sprite has its own pen. Buttons send a message; the pencil changes its own pen.
The colour variable carries the colour code.

Quick-fire

Your pencil’s pen is pink. Then a script runs set pen color to [#FFFFFF]. You draw over a pink line. What do you see?

Reveal the answer

The pink line disappears where you drew. White on white paper looks like nothing at all. You have just built an eraser.

Today’s Topic 3 min

change pen (color v) by (2) — a rainbow line
An eraser is a white pen
stamp — printing the sprite onto the paper
A tool variable that holds a word

Learning outcome

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

Make the pen change colour as it draws.
Stamp a copy of a sprite onto the Stage.
Use one variable to switch between tools.

Learnt — one pencil, many tools 28 min

1 · A rainbow line

The pen has a colour number as well as a colour code. It runs from 0 to 100, round the rainbow: red, orange, yellow, green, blue, purple, and back to red.


when flag clicked
erase all
set pen color to [#FF0000]
set pen size to (10)
pen down
repeat (80)
  change x by (5)
  change y by (pick random (-6) to (6))
  change pen (color v) by (2)
end
pen up

Every step moves the colour number on by 2.

WHAT IT SHOULD LOOK LIKE

One line, and the colour number moves on by 2 at every step.

80 steps

Runs here in the page. Nothing to install.

How to use this: Click the green flag to start it. Nothing else to press — watch the line change colour as it grows.

One block in the loop turns one line into a rainbow.

Past 100 the number goes back round to 0. So the rainbow never runs out.

2 · An eraser is a white pen

Scratch has no rub-out block. But the paper is white. A fat white pen over a line hides it.


set pen color to [#FFFFFF]
set pen size to (30)

Two blocks turn the pencil into an eraser.

WHAT IT SHOULD LOOK LIKE

A fat white pen over a blue line. On white paper, that is an eraser.

the white pen runs over the middle

Runs here in the page. Nothing to install.

How to use this: Click the green flag to start it. Nothing else to press — watch the middle of the line vanish.

A blue line, then the white pen runs over its middle.

3 · Stamp

stamp prints the sprite’s costume onto the paper, like a rubber stamp. The sprite can then move on. The print stays until erase all.


when flag clicked
erase all
go to x: (-180) y: (-20)
repeat (7)
  stamp
  wait (0.3) seconds
  change x by (60)
  change [color v] effect by (25)
end

The stamp copies the colour effect too.

WHAT IT SHOULD LOOK LIKE

Stamp, move, stamp. One star sprite leaves seven stars on the paper.

seven stamps

Runs here in the page. Nothing to install.

How to use this: Click the green flag to start it. Nothing else to press — watch the row of stars appear.

Seven stars on the paper, one Star sprite.

4 · A tool variable

Now the pencil can be a pencil, a rainbow brush or an eraser. It needs to know which. A variable called tool holds the word.


when [2 v] key pressed
set [tool v] to [rainbow]
set pen size to (8)

A key picks the tool.


if <(tool) = [rainbow]> then
  change pen (color v) by (3)
end
pen down

The loop asks before it draws.

You used the same idea in Level 3, when a state variable held menu or play.

Basic — three tools 25 min

Open your sketch pad from last lesson.

Step 1 — the variable

Make a variable called tool, for all sprites. Tick it so it shows.
In the pencil’s green-flag script, add set [tool v] to [pencil].

Step 2 — three keys

Key 1: set [tool v] to [pencil], set pen size to (4), set pen color to (colour).
Key 2: set [tool v] to [rainbow], set pen size to (8).
Key 3: set [tool v] to [eraser], set pen size to (24), set pen color to [#FFFFFF].

Step 3 — the loop asks

Find the pen down inside your drawing loop.
Just above it, add if <(tool) = [rainbow]> then holding change pen (color v) by (3).

Step 4 — a colour click means the pencil

In when I receive [new colour v], add set [tool v] to [pencil] and set pen size to (4).
Test: press 3, rub something out, then click a ball. You are drawing again.


when flag clicked
go to [back v] layer
erase all
set [colour v] to [#4C4CFF]
set [tool v] to [pencil]
set pen color to (colour)
set pen size to (4)
forever
  go to [mouse-pointer v]
  if <<mouse down?> and <(mouse y) < (130)>> then
    if <(tool) = [rainbow]> then
      change pen (color v) by (3)
    end
    pen down
  else
    pen up
  end
end

when [3 v] key pressed
set [tool v] to [eraser]
set pen size to (24)
set pen color to [#FFFFFF]

The pencil’s main loop, and the eraser key. Keys 1 and 2 look like key 3.

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then click the stage once. Press 1, 2 or 3 to pick a tool, then hold the mouse button down and drag. Click a ball to pick a colour.

What you are aiming at: three tools, and the readout says which one you hold.

After the eraser, the pencil draws white.

Key 1 is missing set pen color to (colour). The pen stays white until something changes it back.

The rainbow is all one colour.

The change is outside the if, or the word in the if is not exactly rainbow. Check the spelling in both places.

CHALLENGE 1 · L4-03-M1🪙 30 Adcoins8 min

Say the tool

Every time the tool changes, the pencil says its name for 1 second.
This works for the keys and for a click on a ball.

WHAT IT SHOULD LOOK LIKE

Challenge 1 — every time you switch, the pencil says which tool it is holding.

press 3

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then click the stage once. Press 1, 2 or 3, or click a ball, and watch the Pencil.

The pencil names the tool every time it changes.

Done when: pressing 1, 2, 3 and clicking a ball each make the pencil say the right word.

Teacher reveal

Add say (tool) for (1) seconds at the end of all four scripts. Saying the variable, not the word, means one block works everywhere.

CHALLENGE 2 · L4-03-M2🪙 50 Adcoins9 min

A stamp tool

Key 4 picks the stamp tool. The pencil turns into a star.
Each click on the paper prints one star.
Holding the button down still prints only one.
Keys 1, 2 and 3 turn it back into a pencil.

WHAT IT SHOULD LOOK LIKE

Challenge 2 — a stamp tool. One click, one star. Holding the button does not smear.

key 4, five clicks

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then click the stage once and press 4. Click on the stage to stamp stars. Press 1 to go back to the pencil.

One click, one star.

Done when: five clicks give exactly five stars, and pressing 1 gives you the pencil back.

Teacher reveal

Add a star costume to the pencil. In the loop, before the rainbow check:


if <(tool) = [stamp]> then
  stamp
  wait until <not <mouse down?>>
else
  pen down
end

The wait until <not <mouse down?>> is what stops the smear. Key 4 also does pen up and switches costume.

CHALLENGE 3 · L4-03-M3🪙 70 Adcoins10 min

A spray can

Key 5 picks the spray can.
While you hold the button, little dots land near the mouse, not on it.
No line joins the dots.
It uses the colour you picked.

WHAT IT SHOULD LOOK LIKE

Challenge 3 — a spray can. A puff of dots lands round the mouse while you hold the button.

key 5, then drag

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then click the stage once and press 5. Hold the mouse button down and drag to spray.

A cloud of dots, thicker where you go slowly.

Done when: a slow drag leaves a cloud of separate dots, and a fast drag leaves a thin trail of them.

Teacher reveal


if <(tool) = [spray]> then
  pen up
  repeat (6)
    go to x: ((mouse x) + (pick random (-20) to (20))) y: ((mouse y) + (pick random (-20) to (20)))
    pen down
    pen up
  end
end

Pen down then pen up in the same place draws one dot. The pen up before each jump is what stops the dots joining.

EXTRA MISSION · L4-03-MX🪙 100 Adcoinsbonus

A straight-line tool

Hands are wobbly. Give the app a ruler.

Key 6 picks the line tool.
Press the button, drag, and let go.
One straight line appears, from where you pressed to where you let go.
Nothing is drawn while you are dragging.

WHAT IT SHOULD LOOK LIKE

Extra — press, drag, let go. One straight line from where you pressed to where you let go.

press here … let go there

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then click the stage once and press 6. Press the mouse button, drag, and let go.

Press, drag, let go: one straight line.

Teacher reveal


if <(tool) = [line]> then
  pen up
  set [start x v] to (mouse x)
  set [start y v] to (mouse y)
  wait until <not <mouse down?>>
  go to x: (start x) y: (start y)
  pen down
  go to [mouse-pointer v]
  pen up
end

Summary 5 min

change pen (color v) by (2) walks the colour round the rainbow, 0 to 100.
An eraser is a white pen on white paper.
stamp prints the costume onto the paper.
One variable holding a word decides what a drag does.

Colour number: The pen’s colour as a number from 0 to 100, round the rainbow.
Stamp: A print of the sprite’s costume left on the Stage.
Tool: What a drag does right now: draw, rainbow, erase or stamp.

Hand in

Save your sketch pad. Next lesson a second pencil copies every move you make, and you get the app ready to share.

Learnt28 min · rainbow colour, a white eraser, stamp, a tool variable
Basic25 min · three tools on 1, 2 and 3
Challenge 1–327 min · say the tool, a stamp tool, a spray can
Extrabonus · a straight-line tool

WHAT IT SHOULD LOOK LIKE

One pencil, three tools. A number key picks the tool; the tool decides what a drag does.

key 2, then drag

Review — Sketch Pad II 5 min

set pen color to [#D400AB] and set pen size to (8) change the next line.
Every sprite has its own pen. Buttons send a message; the pencil changes its own pen.
The colour variable carries the colour code.

Quick-fire

Your pencil’s pen is pink. Then a script runs set pen color to [#FFFFFF]. You draw over a pink line. What do you see?

Reveal the answer

The pink line disappears where you drew. White on white paper looks like nothing at all. You have just built an eraser.

Today’s Topic 3 min

change pen (color v) by (2) — a rainbow line
An eraser is a white pen
stamp — printing the sprite onto the paper
A tool variable that holds a word

Learning outcome

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

Make the pen change colour as it draws.
Stamp a copy of a sprite onto the Stage.
Use one variable to switch between tools.

Learnt — one pencil, many tools 28 min

1 · A rainbow line

The pen has a colour number as well as a colour code. It runs from 0 to 100, round the rainbow: red, orange, yellow, green, blue, purple, and back to red.


when flag clicked
erase all
set pen color to [#FF0000]
set pen size to (10)
pen down
repeat (80)
  change x by (5)
  change y by (pick random (-6) to (6))
  change pen (color v) by (2)
end
pen up

Every step moves the colour number on by 2.

WHAT IT SHOULD LOOK LIKE

One line, and the colour number moves on by 2 at every step.

80 steps

Runs here in the page. Nothing to install.

How to use this: Click the green flag to start it. Nothing else to press — watch the line change colour as it grows.

One block in the loop turns one line into a rainbow.

Past 100 the number goes back round to 0. So the rainbow never runs out.

2 · An eraser is a white pen

Scratch has no rub-out block. But the paper is white. A fat white pen over a line hides it.


set pen color to [#FFFFFF]
set pen size to (30)

Two blocks turn the pencil into an eraser.

WHAT IT SHOULD LOOK LIKE

A fat white pen over a blue line. On white paper, that is an eraser.

the white pen runs over the middle

Runs here in the page. Nothing to install.

How to use this: Click the green flag to start it. Nothing else to press — watch the middle of the line vanish.

A blue line, then the white pen runs over its middle.

3 · Stamp

stamp prints the sprite’s costume onto the paper, like a rubber stamp. The sprite can then move on. The print stays until erase all.


when flag clicked
erase all
go to x: (-180) y: (-20)
repeat (7)
  stamp
  wait (0.3) seconds
  change x by (60)
  change [color v] effect by (25)
end

The stamp copies the colour effect too.

WHAT IT SHOULD LOOK LIKE

Stamp, move, stamp. One star sprite leaves seven stars on the paper.

seven stamps

Runs here in the page. Nothing to install.

How to use this: Click the green flag to start it. Nothing else to press — watch the row of stars appear.

Seven stars on the paper, one Star sprite.

4 · A tool variable

Now the pencil can be a pencil, a rainbow brush or an eraser. It needs to know which. A variable called tool holds the word.


when [2 v] key pressed
set [tool v] to [rainbow]
set pen size to (8)

A key picks the tool.


if <(tool) = [rainbow]> then
  change pen (color v) by (3)
end
pen down

The loop asks before it draws.

You used the same idea in Level 3, when a state variable held menu or play.

Basic — three tools 25 min

Open your sketch pad from last lesson.

Step 1 — the variable

Make a variable called tool, for all sprites. Tick it so it shows.
In the pencil’s green-flag script, add set [tool v] to [pencil].

Step 2 — three keys

Key 1: set [tool v] to [pencil], set pen size to (4), set pen color to (colour).
Key 2: set [tool v] to [rainbow], set pen size to (8).
Key 3: set [tool v] to [eraser], set pen size to (24), set pen color to [#FFFFFF].

Step 3 — the loop asks

Find the pen down inside your drawing loop.
Just above it, add if <(tool) = [rainbow]> then holding change pen (color v) by (3).

Step 4 — a colour click means the pencil

In when I receive [new colour v], add set [tool v] to [pencil] and set pen size to (4).
Test: press 3, rub something out, then click a ball. You are drawing again.


when flag clicked
go to [back v] layer
erase all
set [colour v] to [#4C4CFF]
set [tool v] to [pencil]
set pen color to (colour)
set pen size to (4)
forever
  go to [mouse-pointer v]
  if <<mouse down?> and <(mouse y) < (130)>> then
    if <(tool) = [rainbow]> then
      change pen (color v) by (3)
    end
    pen down
  else
    pen up
  end
end

when [3 v] key pressed
set [tool v] to [eraser]
set pen size to (24)
set pen color to [#FFFFFF]

The pencil’s main loop, and the eraser key. Keys 1 and 2 look like key 3.

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then click the stage once. Press 1, 2 or 3 to pick a tool, then hold the mouse button down and drag. Click a ball to pick a colour.

What you are aiming at: three tools, and the readout says which one you hold.

After the eraser, the pencil draws white.

Key 1 is missing set pen color to (colour). The pen stays white until something changes it back.

The rainbow is all one colour.

The change is outside the if, or the word in the if is not exactly rainbow. Check the spelling in both places.

CHALLENGE 1 · L4-03-M1🪙 30 Adcoins8 min

Say the tool

Every time the tool changes, the pencil says its name for 1 second.
This works for the keys and for a click on a ball.

WHAT IT SHOULD LOOK LIKE

Challenge 1 — every time you switch, the pencil says which tool it is holding.

press 3

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then click the stage once. Press 1, 2 or 3, or click a ball, and watch the Pencil.

The pencil names the tool every time it changes.

Done when: pressing 1, 2, 3 and clicking a ball each make the pencil say the right word.

Teacher reveal

Add say (tool) for (1) seconds at the end of all four scripts. Saying the variable, not the word, means one block works everywhere.

CHALLENGE 2 · L4-03-M2🪙 50 Adcoins9 min

A stamp tool

Key 4 picks the stamp tool. The pencil turns into a star.
Each click on the paper prints one star.
Holding the button down still prints only one.
Keys 1, 2 and 3 turn it back into a pencil.

WHAT IT SHOULD LOOK LIKE

Challenge 2 — a stamp tool. One click, one star. Holding the button does not smear.

key 4, five clicks

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then click the stage once and press 4. Click on the stage to stamp stars. Press 1 to go back to the pencil.

One click, one star.

Done when: five clicks give exactly five stars, and pressing 1 gives you the pencil back.

Teacher reveal

Add a star costume to the pencil. In the loop, before the rainbow check:


if <(tool) = [stamp]> then
  stamp
  wait until <not <mouse down?>>
else
  pen down
end

The wait until <not <mouse down?>> is what stops the smear. Key 4 also does pen up and switches costume.

CHALLENGE 3 · L4-03-M3🪙 70 Adcoins10 min

A spray can

Key 5 picks the spray can.
While you hold the button, little dots land near the mouse, not on it.
No line joins the dots.
It uses the colour you picked.

WHAT IT SHOULD LOOK LIKE

Challenge 3 — a spray can. A puff of dots lands round the mouse while you hold the button.

key 5, then drag

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then click the stage once and press 5. Hold the mouse button down and drag to spray.

A cloud of dots, thicker where you go slowly.

Done when: a slow drag leaves a cloud of separate dots, and a fast drag leaves a thin trail of them.

Teacher reveal


if <(tool) = [spray]> then
  pen up
  repeat (6)
    go to x: ((mouse x) + (pick random (-20) to (20))) y: ((mouse y) + (pick random (-20) to (20)))
    pen down
    pen up
  end
end

Pen down then pen up in the same place draws one dot. The pen up before each jump is what stops the dots joining.

EXTRA MISSION · L4-03-MX🪙 100 Adcoinsbonus

A straight-line tool

Hands are wobbly. Give the app a ruler.

Key 6 picks the line tool.
Press the button, drag, and let go.
One straight line appears, from where you pressed to where you let go.
Nothing is drawn while you are dragging.

WHAT IT SHOULD LOOK LIKE

Extra — press, drag, let go. One straight line from where you pressed to where you let go.

press here … let go there

Runs here in the page. Nothing to install.

How to use this: Click the green flag, then click the stage once and press 6. Press the mouse button, drag, and let go.

Press, drag, let go: one straight line.

Teacher reveal


if <(tool) = [line]> then
  pen up
  set [start x v] to (mouse x)
  set [start y v] to (mouse y)
  wait until <not <mouse down?>>
  go to x: (start x) y: (start y)
  pen down
  go to [mouse-pointer v]
  pen up
end

Summary 5 min

change pen (color v) by (2) walks the colour round the rainbow, 0 to 100.
An eraser is a white pen on white paper.
stamp prints the costume onto the paper.
One variable holding a word decides what a drag does.

Colour number: The pen’s colour as a number from 0 to 100, round the rainbow.
Stamp: A print of the sprite’s costume left on the Stage.
Tool: What a drag does right now: draw, rainbow, erase or stamp.

Hand in

Save your sketch pad. Next lesson a second pencil copies every move you make, and you get the app ready to share.