[Feature] Text layout engine

[vmarcella]

Overview

Add text layout that handles line breaking, alignment, and positioning of
glyphs for a given text string.

Current State

No response

Scope

Goals:

• Single-line text layout
• Multi-line text with word wrapping
• Horizontal alignment (left, center, right)
• Vertical alignment (top, middle, bottom)
• Measure text dimensions before rendering

Non-Goals:

• Rich text (multiple fonts/styles)
• Bidirectional text
• Justification

Proposed API

pub enum TextAlign {
  Left,
  Center,
  Right,
}

pub enum TextWrap {
  None,
  Word,
  Character,
}

pub struct TextLayout {
  glyphs: Vec<PositionedGlyph>,
  bounds: [f32; 4], // x, y, width, height
}

pub struct PositionedGlyph {
  pub character: char,
  pub position: [f32; 2],
  pub uv: GlyphUV,
}

pub struct TextLayoutBuilder {
  font: Handle<Font>,
  size: f32,
  align: TextAlign,
  wrap: TextWrap,
  max_width: Option<f32>,
}

impl TextLayoutBuilder {
  pub fn new(font: Handle<Font>, size: f32) -> Self;
  pub fn with_align(self, align: TextAlign) -> Self;
  pub fn with_wrap(self, wrap: TextWrap, max_width: f32) -> Self;
  pub fn layout(self, text: &str, atlas: &mut GlyphAtlas) -> TextLayout;
}

impl TextLayout {
  pub fn bounds(&self) -> [f32; 4];
  pub fn glyphs(&self) -> &[PositionedGlyph];
}

Acceptance Criteria

• Single line text layouts correctly
• Word wrap breaks at spaces
• Alignment positions text correctly
• Bounds calculation is accurate
• Empty string produces empty layout

Affected Crates

lambda-rs

Notes

• Kerning improves appearance (if font supports)
• Consider Unicode line breaking algorithm later