03. Inputs and Controls

The Froth Machine gives you two friendly input families first:

  • joy.*? for the joystick
  • knob.* for the two potentiometers

That is enough for menus, drawing toys, cursor control, and small games.

The Joystick

The joystick words are:

joy.up?:
joy.down?:
joy.left?:
joy.right?:
joy.click?:

Each one returns a boolean.

That means the usual shape is:

when joy.left?:  [ ... ]
when joy.right?: [ ... ]
when joy.click?: [ ... ]

For first-time work, treat the joystick as “five little buttons with names”.

The Knobs

The knob words are:

knob.left:
knob.right:
knob.left.raw:
knob.right.raw:

The usual front-door words are knob.left and knob.right. They give you a percentage-style reading that is easy to map onto board coordinates or speeds.

The *.raw variants are there when you want the ADC reading directly.

Mapping A Knob Onto The Screen

Here is a simple board control loop driven by the knobs:

to scaleKnob with percent, max [
  percent * max / 100
]

dot.frame is fn [
  here x is scaleKnob: knob.left:, (grid.width - 1);
  here y is scaleKnob: knob.right:, (grid.height - 1);
  grid.clear:;
  grid.set: x, y, true;
  grid.show:
]

repeat 80 [
  dot.frame:;
  ms: 30
]

This is a nice early exercise because it teaches the whole control shape:

  • read input
  • turn it into game or drawing state
  • draw the current state
  • show the result

Raw Buttons

The board also exposes raw button pin names such as BUTTON_1, BUTTON_2, and BUTTON_3.

There is not a dedicated button.* helper family yet, so the raw shape is:

gpio.input: BUTTON_2
gpio.read: BUTTON_2

If you want a boolean helper, write one exactly the way the joystick helpers work:

button.two? is fn [
  gpio.input: BUTTON_2;
  (gpio.read: BUTTON_2) == 0
]

That is the right move when you discover you are asking the same raw GPIO question over and over.

One Important Board Quirk

BUTTON_1 and A0 share the same raw GPIO on the mounted workshop board.

That means:

  • A0 is not a separate dedicated workshop button input
  • if you want clean first-time input work, prefer joy.*? and knob.*
  • use the raw button path only when you really mean to work at that level

What Input Usually Feeds

On this board, input most often feeds one of three things:

  • position: a cursor, paddle, or sprite
  • mode: pause, resume, clear, reset
  • timing: speed, delay, difficulty

That is why the input layer is small but effective. The board is tiny, so clear named inputs matter more than a huge helper stack.

Next: Games and loops .