Geometry Art IV

Review — Lesson 7 5 min

• Draw a shape, turn, draw it again — and you get a pattern.
• The pattern closes when copies × turn = 360.
• flower (petals) (sides) (size) :: custom calls your polygon block.

Quick-fire

A flower has 9 petals. How far does the arrow turn between petals?

Today’s Topic 3 min

• Run without screen refresh — a block that finishes before the Stage is shown
• Variables on keys, and a redraw block
• A gallery of designs kept in lists
• Shipping the project so other people can play it

Learning outcome

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

1. Explain what Run without screen refresh changes.
2. Change a drawing with keys and redraw it at once.
3. Save and load settings using lists.

Learnt — make it fast, then make it a toy 28 min

1 · A slow spirograph

A circle is a polygon with lots of sides. Draw 24 circles, turning 15 degrees between them, and you get a spirograph — the pattern from the toy with the gear wheels.

repeat (24)
  polygon (20) (12) :: custom
  turn cw (15) degrees
  change pen (color v) by (4)
end
            

2 · Run without screen refresh

Normally Scratch draws the Stage again after each step of a loop, so you can watch. That is why everything so far has been slow enough to see. You can switch that off for a My Block:

1. Right-click your define hat and choose Edit.
2. Tick Run without screen refresh. Click OK.
3. Now the whole block finishes first. The Stage shows only the end result.

define spiro
erase all
set pen size to (2)
set pen (color v) to (hue)
pen up
go to x: (0) y: (0)
point in direction (90)
pen down
repeat (24)
  polygon (20) (12) :: custom
  turn cw (15) degrees
  change pen (color v) by (4)
end
pen up

when [space v] key pressed
change [hue v] by (20)
spiro :: custom
            

3 · Numbers on keys

Put the flower’s numbers into variables. A key changes a variable, then calls redraw. Because redraw runs without screen refresh, the new pattern appears straight away.

define redraw
erase all
pen up
go to x: (0) y: (0)
point in direction (90)
pen down
set pen (color v) to (hue)
flower (petals) (sides) (size) :: custom
pen up

when [up arrow v] key pressed
change [petals v] by (1)
redraw :: custom

when [right arrow v] key pressed
change [sides v] by (1)
redraw :: custom
            

Basic — the pattern machine 24 min

Open your project with the polygon and flower blocks.

Step 1 — the variables

1. Make four variables: petals, sides, size and hue.
2. Tick petals and sides so they show on the Stage.

Step 2 — the redraw block

1. Make a Block called redraw. Tick Run without screen refresh.
2. Build the redraw stack from the Learnt.

Step 3 — the flag

1. Under the flag: set pen size to (2).
2. Set petals to 12, sides to 5, size to 50 and hue to 80.
3. Call redraw :: custom.

Step 4 — the keys

1. Up arrow: petals goes up by 1, then redraw.
2. Down arrow: petals goes down by 1, then redraw.
3. Right arrow: sides goes up by 1. Left arrow: sides goes down by 1. Both redraw.

when flag clicked
set pen size to (2)
set [petals v] to (12)
set [sides v] to (5)
set [size v] to (50)
set [hue v] to (80)
redraw :: custom

when [down arrow v] key pressed
change [petals v] by (-1)
redraw :: custom

when [left arrow v] key pressed
change [sides v] by (-1)
redraw :: custom
            

Dials with stops

A real dial cannot turn for ever. Give yours stops, and add a size dial.

• Petals stay between 3 and 24.
• Sides stay between 3 and 10.
• W makes the pattern bigger and S makes it smaller, in steps of 5, between 20 and 70.
• Show size on the Stage too.

when [w v] key pressed
if <(size) < (70)> then
  change [size v] by (5)
end
redraw :: custom
            

The surprise key

Press R and the machine invents a pattern for you.

• R picks random petals (5 to 20), sides (3 to 8) and size (25 to 55).
• R picks a random colour too.
• The boxes on the Stage show what was picked.

when [r v] key pressed
set [petals v] to (pick random (5) to (20))
set [sides v] to (pick random (3) to (8))
set [size v] to (pick random (25) to (55))
set [hue v] to (pick random (0) to (100))
redraw :: custom
            

A gallery in lists

Keep four favourite designs in three lists — one for petals, one for sides, one for size. Row 1 of every list is design 1, row 2 is design 2, and so on.

• Make lists g petals, g sides and g size with four rows each.
• Keys 1, 2, 3 and 4 show that design.
• A box on the Stage says which design is showing.

define show design (n)
set [design v] to (n)
set [petals v] to (item (n) of [g petals v])
set [sides v] to (item (n) of [g sides v])
set [size v] to (item (n) of [g size v])
set [hue v] to ((n) * (25))
redraw :: custom

when [2 v] key pressed
show design (2) :: custom
            

Save your own designs — and ship it

Let the player fill the gallery. Then share the project so other people can play.

• The flag empties the gallery lists and draws a starting pattern.
• The arrows design a pattern. S saves it to the end of the lists.
• A saved box shows how many designs are saved.
• Keys 1, 2 and 3 bring back a saved design — but only if it exists.
• The arrow tells the player which keys to use.

when [s v] key pressed
add (petals) to [g petals v]
add (sides) to [g sides v]
add (size) to [g size v]
set [saved v] to (length of [g petals v])
say (join [Saved as design ] (saved)) for (1.5) seconds

when [3 v] key pressed
if <not <(length of [g petals v]) < (3)>> then
  set [petals v] to (item (3) of [g petals v])
  set [sides v] to (item (3) of [g sides v])
  set [size v] to (item (3) of [g size v])
  redraw :: custom
end
            

Summary 5 min

• Run without screen refresh makes a My Block finish before the Stage is shown.
• Never put a wait or a forever inside a block that runs without screen refresh.
• Keys change variables; one redraw block draws the result.
• Lists kept in step can hold a whole gallery of settings.

Screen refresh

Scratch showing the Stage again. Normally it happens after every step of a loop.

Generator

A program that makes new things from a few settings.

Spirograph

A pattern of circles turned round a centre, like the toy with gear wheels.

Hand in

Share your pattern machine and keep the link. That is the end of Geometry Art. Next lesson a new arc begins: Music Maker, where code plays the notes.