Editing Lua extension API (section)

== Controls ==
Controls create ordinary transmitter widgets and provide live values to callbacks. An ID must start with a letter or underscore, contain only letters, digits, and underscores, and contain at most 64 characters. Control and input IDs in one modulation must be unique.

The helper form is recommended:
<syntaxhighlight lang="lua">
controls = {
  simtx.controls.slider("gain", {
    label = "Gain", help = "Linear input gain.", unit = "x",
    precision = 2, min = 0, max = 2, step = 0.01, default = 1,
  }),
  simtx.controls.toggle("enabled", {label = "Enabled", default = true}),
  simtx.controls.text("message", {label = "Message", default = "CQ"}),
  simtx.controls.choice("shape", {
    label = "Shape",
    options = {
      "soft",
      {value = "hard", label = "Hard edges"},
    },
    default = "soft",
  }),
}
</syntaxhighlight>

The equivalent long form is a table with an <code>id</code> and <code>type</code>. The slider aliases are <code>range</code> and <code>number</code>. Checkbox aliases are <code>check</code>, <code>bool</code>, <code>boolean</code>, and <code>toggle</code>. <code>string</code> is a text alias. Choice aliases are <code>select</code>, <code>dropdown</code>, and <code>combo</code>.

{| class="wikitable"
! Control !! Fields and defaults !! Lua value
|-
| Slider || <code>min=0</code>, <code>max=1</code>, <code>step=0</code>, <code>default=min</code>, optional <code>unit</code> and <code>precision</code> || Number
|-
| Checkbox || <code>default=false</code> || Boolean
|-
| Text || <code>default=""</code> || String
|-
| Choice || Non-empty <code>options</code>; <code>default</code> is the first option || String value
|}

All controls accept <code>label</code>, <code>help</code>, and <code>default</code>. A label defaults to the ID. Help text may contain at most 300 characters. Slider units may contain at most 16 characters. Slider precision may be 0 to 8, or may be omitted so the interface derives it from the step. Slider values and bounds must be finite, <code>max</code> must exceed <code>min</code>, and the default must be within the range.