@font-face: load and parse web fonts #125

Overview#

Implement @font-face support to load and parse web fonts, using the existing text crate for font parsing and net crate for network fetching.

Requirements#

Parsing#

• Parse @font-face rule with descriptors:
  • font-family: the family name to register
  • src: url() references (WOFF2 not required initially; TTF/OTF via URL)
  • font-weight: normal, bold, or numeric (100-900)
  • font-style: normal, italic, oblique
  • font-display: auto, block, swap, fallback, optional
  • unicode-range (optional, can defer)

Font Loading#

• Fetch font files via net crate when @font-face rules are encountered
• Support url() sources (absolute and relative URLs)
• Implement font loading states: loading → loaded / failed
• font-display controls rendering behavior during load:
  • swap: use fallback immediately, swap when loaded
  • block: invisible text briefly, then fallback
  • fallback: short block period, short swap period
  • optional: very short block period, no swap

Font Registration#

• Parse downloaded font bytes with text crate's OTF/TTF parser
• Register the font under the declared font-family name
• Integrate with font matching: when layout requests a font-family, check @font-face fonts before system fonts
• Match by weight and style

Integration#

• Extend CSS @font-face parsing in crates/css/
• Add font loading to resource loader in crates/browser/ or crates/net/
• Integrate with font discovery in crates/text/
• Trigger relayout when web fonts finish loading

Acceptance Criteria#

• @font-face { font-family: "MyFont"; src: url(...); } parses correctly
• Font files are fetched from URLs
• Downloaded fonts are parsed and available for text rendering
• font-family: "MyFont" in CSS matches the web font
• Fallback to system font works when web font fails to load
• font-display: swap shows fallback then swaps
• Relayout occurs when web font finishes loading
• All existing tests continue to pass
• New unit tests for @font-face parsing and font matching