VDMX table

Stores pre-computed vertical device metrics to prevent clipping at specific pixel sizes on Windows.

Scope

• Format family: Shared SFNT
• Table tag in JSON: VDMX

Specs

• (No explicit spec URL found in implementation source)
• OpenType table registry: https://learn.microsoft.com/en-us/typography/opentype/spec/otff#font-tables

JSON Skeleton

This skeleton reflects fields currently parsed/written by Font Flux JS for this table.

{
  "tables": {
    "VDMX": {
      "version": 0,
      "ratios": null,
      "groups": null,
      "numRecs": 0,
      "_checksum": 0
    }
  }
}

Top-level Fields

• version - number (0..65535)
• ratios - implementation-defined
• groups - implementation-defined
• numRecs - number (0..65535)

Additional Nested Keys Seen In Implementation

• bCharSet
• xRatio
• yStartRatio
• yEndRatio
• groupIndex
• ratios
• yPelHeight
• yMax
• yMin

Notes

• Preserve _checksum for stable round-tripping.
• If a table is only partially understood, prefer keeping unknown bytes in _raw instead of dropping data.
• Validate with .validate() after edits.