tryst-value-slider

A single-thumb value slider for tryst, Crystal's Tcl/Tk binding — a rounded track with a filled portion, an antialiased thumb, optional tick marks with min/max labels, and a value bubble that tracks the thumb while dragging or keyboard-adjusting. Built on Tryst::OwnerDrawnWidget and rendered through tryst-vector.

require "tryst"
require "tryst-value-slider"

app = Tryst::App.new
slider = Tryst::ValueSlider.new(app, min: 0.0, max: 100.0, step: 1.0, value: 65.0, ticks: 5)
slider.pack(fill: "x", padx: 16, pady: 8)

slider.on_change { |v| puts "volume now #{v.round.to_i}%" }

app.show
app.mainloop

From examples/value_slider_demo.cr.

It's just a widget: #pack/#grid place it, #value/#value= read and set it, #on_change fires on every user-driven change (drag, click-to-position, or keyboard) but never for a programmatic #value= — the same split every other stateful widget in this codebase draws. Nothing about it being canvas-backed or ThorVG-rendered is part of its own public surface. format: (a Proc(Float64, String)) controls the bubble's text; accent: overrides the theme-derived default with a #rrggbb hex string. See examples/value_slider_demo.cr for a runnable version with ticks, a custom format, and a disabled slider side by side.

The bubble is a fixed size, not shrink-to-fit around whatever the current value renders as — sizing it to the live text made the whole bubble visibly wobble while dragging the moment the string length itself changed (e.g. "1.0" vs "1.25"). By default the width is max(format(min), format(max)), measured once at construction; bubble_width: (pixels) overrides that guess outright, for a custom format: whose widest output isn't at either end of the range.

font: defaults to "TkTextFont" (Tk's own named font, resolving to whatever system UI face each platform uses) and applies to all three labels (min, max, bubble) — pass any real Tk font spec (another named font, or a literal "family size" string) to override it.

The default accent color comes from Tryst::Theme#accent (the active ttk theme's own -selectbackground), so it already matches aqua/clam/vista rather than a hardcoded color.

Requirements

Whatever tryst and tryst-vector need - Crystal >= 1.21.0, Tcl/Tk 8.6, and ThorVG >= 1.0 (see tryst-vector's own README for per-platform package names and why).

Examples

crystal run examples/value_slider_demo.cr

Tests

shards install
crystal spec                    # host
scripts/docker-test.sh          # Debian forky, same suite

scripts/docker-test.sh builds from this repo's own root; shards install inside the image fetches tryst and tryst-vector directly via their github: dependencies. It takes the same arguments crystal spec does, so a focused run works there too.