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Switch Specs

This document captures design and implementation notes for Switch.

For end-user usage and examples, see Switch.

Overview

  • Status: Implemented
  • Primary purpose: A compact toggle switch with optional inline content (label) rendered next to the track.
  • Content model: Switch : ContentVisual (single child Content).
  • Interaction:
    • toggles on Space/Enter and left click
    • supports Left/Right to force off/on
  • Rendering note: Carefully handles RGBA track fills to avoid double-applied alpha blending when drawing the thumb over the track.

Public API surface

Type

  • Switch : ContentVisual (sealed)

Constructors

  • Switch() sets Focusable = true.
  • Switch(Visual content) assigns Content.

Bindable properties

  • IsOn : bool
    • raises the Toggled routed event when it changes
  • IsPressed : bool (read-only public)
    • set during pointer press/release for pressed styling

Routed events

  • Toggled (bubble): raised with old/new boolean values.

Layout & rendering

Measure

  • Track width is fixed at 4 cells (TrackWidth = 4).
  • If there is content:
    • measures content with width reduced by TrackWidth + SwitchStyle.SpaceBetweenGlyphAndText
    • desired size is:
      • width = TrackWidth + gap + contentWidth
      • height = max(1, contentHeight)
  • If no content: desired size is (TrackWidth, 1).

Arrange

  • Content is arranged to the right of the track + gap within finalRect.
  • The track itself is drawn in Render and is vertically centered within the control’s height.

Render

Track rendering:

  • Draws up to min(TrackWidth, Bounds.Width) cells for the track.
  • Uses SwitchStyle.TrackLeft/TrackRight for the first/last cell glyphs, spaces otherwise.
  • Resolves per-segment track style with SwitchStyle.ResolveTrackPart(...):
    • segments are considered “active” based on IsOn and thumb position
    • hovered/pressed/focused variants are applied by the style resolver

Thumb rendering:

  • Computes a thumbIndex:
    • for full 4-cell track: index is 1 (off) or 2 (on)
    • for smaller tracks, clamps to the available range
  • Renders SwitchStyle.ThumbGlyphOn / ThumbGlyphOff over the track.
  • Avoids double alpha blending:
    • if the track background is RGBA, the thumb style is not merged with the track style
    • otherwise, merges unspecified style parts from the track into the thumb (MergeUnspecified)

Interaction

Keyboard

  • Space / Enter: toggle
  • Left: set IsOn = false
  • Right: set IsOn = true

Pointer

  • left press sets IsPressed = true
  • left release clears IsPressed and toggles IsOn if released within bounds

Styling

SwitchStyle

Key knobs:

  • geometry:
    • SpaceBetweenGlyphAndText
    • TrackLeft / TrackRight
    • ThumbGlyphOn / ThumbGlyphOff (defaults match RadioButtonStyle checked/unchecked glyphs; see SwitchStyle.Round preset)
  • track styles:
    • TrackOn*, TrackOff* (active/inactive parts)
    • TrackHovered, TrackPressed, TrackFocused, TrackDisabled
  • thumb styles:
    • ThumbOn, ThumbOff, ThumbDisabled

Default resolution uses theme colors like Theme.Primary, Theme.Surface, Theme.SurfaceAlt, Theme.Selection, Theme.FocusBorder.

Tests & demos

  • Tests:
    • src/XenoAtom.Terminal.UI.Tests/SwitchTests.cs
  • Demo:
    • ControlsDemo includes switch examples (with and without inline content).

Future / v2 ideas

  • Support configurable track width (while keeping a sensible default).
  • Add optional “animated” toggling (if/when the framework supports lightweight animations).