Sliders

Some values can only be judged by watching them move: how large a model sits in the hand, or how hard a winch pulls. You find those by dragging, not by reasoning about a number. A slider puts one in your mod’s panel as a track you can grab.

Register one

using Hotline.Api;   // Hud, Panel
using UnityEngine;   // Vector3

Hud.RegisterPanel("Yoink", "Yoink (Winch)")
   .Slider("size", 0.2, 2.0, () => WinchItem.HeldScale, v => WinchItem.HeldScale = (float)v, 0.05, "x")
   .Slider("rig height", -0.15, 0.15, () => WinchItem.RigOffset.y,
           v => WinchItem.RigOffset = new Vector3(WinchItem.RigOffset.x, (float)v, WinchItem.RigOffset.z), 0.005, "m")
   .Slider("pull force", 0, 60000, () => Preferences.PullNewtons, v => Preferences.PullNewtons = (float)v, 500, "N")
   .Slider("tool turn", 0, 360, () => WinchItem.HeldRotation.y,
           v => WinchItem.HeldRotation = new Vector3(WinchItem.HeldRotation.x, (float)v, WinchItem.HeldRotation.z), 5, "deg");

(from Yoink’s winch panel, which uses sliders for every value that has to be framed by eye)

The signature:

Panel Slider(string label, double min, double max, Func<double> get, Action<double> set,
             double step = 0d, string unit = null)

Parameter	Meaning
label	printed next to the value, and the source of the slider id (see below)
min / max	the ends of the track. max must be greater than min, or the call is ignored
get	reads the current value; called on the main thread while the panel is drawn
set	applies a new value, on the main thread
step	snap increment. 0 means continuous
unit	short suffix printed after the number (m, N, deg). Optional

The lower-level static form is Hud.RegisterSlider(panelId, label, min, max, get, set, step, unit).

The host owns the range

Hotline clamps to [min, max] and snaps to step before it calls your setter, whichever way the write arrived - a drag in the overlay or hotline slider in the console. Your setter never sees a value outside the range it declared, so it does not have to defend itself:

v => Preferences.PullNewtons = (float)v   // no clamping needed here

Give the range more room than the band you expect to use. A value you cannot reach costs you a rebuild; slack at the ends costs nothing, because the ends are still hard limits.

What it looks like

The panel draws a caption carrying the label and the live value, with a filled track under it. Grab the track and the knob follows the cursor until you release the button, even once the pointer has left the track or the window, so a drag never dies halfway. Printed decimals follow the step, so a 0.005 slider does not read 0 for most of its travel.

From the console

hotline slider <sliderId>          read the value, its range and its step
hotline slider <sliderId> 0.85     write it (clamped and snapped like any other write)

This matters more than it looks. A slider is a mouse control, and no automated harness can drag a mouse. The console command is the same value reachable by typing, which keeps a tuning session reproducible and lets a value you found by eye be read back and written into your defaults.

Ids come from the label, and they collide

A slider’s id is <panelId>:<slug of the label>. Slugging keeps letters and digits, lowercases them, and turns every other run of characters into a single hyphen:

Label	Id in panel Yoink
size	Yoink:size
pull force	Yoink:pull-force
rig height	Yoink:rig-height

Punctuation is dropped, and that is where it bites. Two labels that differ only in punctuation produce the same id, and the second registration silently replaces the first. No warning, no error, no log line: the control is simply not there any more.

"size -0.05"  ->  size-0-05
"size +0.05"  ->  size-0-05     same id, so this one wins and the first vanishes

That exact pair shipped once and removed half a panel’s controls before anyone noticed the count was short. Make every label in a panel differ in its words, not in its symbols: size down and size up rather than size -0.05 and size +0.05.

Rules

• Register from the Unity main thread. get and set are invoked there too, so they may touch game objects.
• max must be greater than min, and both get and set are required. Anything else is dropped silently.
• Re-registering the same id replaces the slider, so re-running your probe is safe.
• Every call is a no-op when Hotline is absent, and on a Hotline older than the one that added sliders.