[Feature] Glyph atlas texture

[vmarcella]

Overview

Create a texture atlas system that packs rasterized glyphs into a single
texture for efficient GPU rendering.

Current State

No response

Scope

Goals:

• Pack multiple glyphs into one texture
• Track UV coordinates for each glyph
• Dynamic atlas growth when full
• Support multiple fonts/sizes in one atlas

Non-Goals:

• SDF generation
• Atlas serialization

Proposed API

pub struct GlyphAtlas {
  texture: Texture,
  glyph_info: HashMap<GlyphKey, GlyphUV>,
}

pub struct GlyphKey {
  pub font_id: u32,
  pub character: char,
  pub size_px: u32, // discretized
}

pub struct GlyphUV {
  pub uv_min: [f32; 2],
  pub uv_max: [f32; 2],
  pub metrics: GlyphMetrics,
}

impl GlyphAtlas {
  pub fn new(gpu: &Gpu, initial_size: u32) -> Self;
  pub fn get_or_insert(&mut self, font: &Font, char: char, size: f32) -> &GlyphUV;
  pub fn texture(&self) -> &Texture;
  pub fn clear(&mut self);
}

Acceptance Criteria

• Glyphs packed into texture
• UV coordinates accurate
• Atlas grows when needed
• Multiple fonts coexist in atlas
• Cache hit returns existing glyph

Affected Crates

lambda-rs

Notes

• Binary tree packing or shelf algorithm
• Consider max atlas size limit