Standard Music Font Layout (SMuFL)

glyphBBoxes

The optional "glyphBBoxes" structure contains information about the actual bounding box for each glyph.¹ The glyph bounding box is defined as the smallest rectangle that encloses every part of the glyph’s path, and is described as a pair of coordinates for the bottom-left (or southwest) and top-right (or northeast) corners of the rectangle, expressed staff spaces to any required degree of precision, relative to the glyph origin.

Below is an excerpt from a dummy font metadata file for Bravura, with a section of the "glyphBBoxes" structure filled in:

{
...
  "glyphBBoxes":
  {
    "brace": {
      "bBoxNE": [
        0.328,
        3.988
      ],
      "bBoxSW": [
        0.008,
        0.0
      ]
    },
    "braceFlat": {
      "bBoxNE": [
        0.36,
        4.084
      ],
      "bBoxSW": [
        0.0,
        0.004
      ]
    },
  ...
  }
}

For each glyph, the "glyphBBoxes" structure provides the glyph’s name and the coordinates of the opposite corners of the bounding rectangle (keys bBoxSW and bBoxNE).