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Padder Specs

This document captures design and implementation notes for Padder.

For end-user usage and examples, see Padder.

Overview

  • Status: Implemented
  • Primary purpose: Adds padding around a single content visual.
  • Role in the framework:
    • lightweight layout primitive for spacing/indent
    • base class for “chrome” controls that need reserved space via an internal inset (e.g. Border)

Public API surface

Type

  • Padder : ContentVisual

Constructors

  • Padder()
  • Padder(Visual content)
  • Padder(Func<Visual> contentFactory)
    • The factory is evaluated during dynamic updates and can rebuild the child when its tracked dependencies change.

Bindables

  • Padding : Thickness
    • Applied around the content, in cells. Negative values are clamped to 0 per side when combined with Inset.

Extensibility point

  • protected virtual Thickness Inset
    • Additional internal padding reserved by derived controls (default: Thickness.Zero).

Layout & rendering

Padder only affects layout; it does not render anything itself.

Effective padding

Internally, Padder uses:

  • EffectivePadding = max(0, Padding + Inset) per side

This allows derived controls to reserve internal chrome space while still allowing user padding.

Measure

  • Computes child constraints by subtracting EffectivePadding.Horizontal/Vertical from the parent max constraints.
  • Measures Content with these inner constraints (or treats content as SizeHints.Fixed(Size.Zero) when null).
  • Returns SizeHints as ContentHints + EffectivePadding, preserving the child’s flex grow/shrink factors.

Arrange

  • Computes an inner rectangle:
    • x = finalRect.X + EffectivePadding.Left
    • y = finalRect.Y + EffectivePadding.Top
    • width = max(0, finalRect.Width - EffectivePadding.Horizontal)
    • height = max(0, finalRect.Height - EffectivePadding.Vertical)
  • Arranges the content into that rectangle (if non-null).

Input & commands

Padder does not handle input and does not expose commands.

Styling

There is no PadderStyle. Visual appearance is determined entirely by the child.

Tests & demos

Tests that lock down current behavior:

  • src/XenoAtom.Terminal.UI.Tests/PadderMeasureArrangeTests.cs

Future / v2 ideas

  • Consider a “background fill” variant (Padder + fill) as a dedicated control if it becomes a common pattern.