Ascender/Descender Extents Checker

Audit observed glyph outline bounds against declared ascent and positive descent magnitude; preserves per-glyph upper/lower overflow, not automatic clipping or font-table truth.

Description

Glyph ink may extend beyond declared ascent and descent.

Glyph ink may extend beyond declared ascent and descent. Signed outline coordinates and positive descent magnitude have different roles.^[1]

Enter nonempty ordered Y-bound pairs and nonnegative declared extents. Return each overflow and any-positive-overflow flag.

When to use Ascender/Descender Extents Checker

Use Ascender/Descender Extents Checker when you need to evaluate the supplied records under the calculation and evidence rules below. No clipping, font-table truth or line-layout behavior is guaranteed.

Prepare measured font or typeset-layout values and the explicit design policy requested. For text or font bytes, use the supported syntax explained below.

How to use Ascender/Descender Extents Checker and understand its results

Prepare measured font or typeset-layout values and the explicit design policy requested. For text or font bytes, use the supported syntax explained below.
Enter glyphYBoundsUnits, declaredAscentUnits, declaredDescentUnits using the field table and calculation rules, then run the tool.
Read glyphAscentOverflowUnits, glyphDescentOverflowUnits, anyVerticalExtentOverflow. The explanation below defines the units, signs, ordering and any flags or placeholder values.
If the tool reports an input issue, correct the values and run it again. Apply the stated assumptions when interpreting a successfully returned result.

Input field	Meaning	Value type; see rules below	Requirement
glyphYBoundsUnits	Glyph y bounds units	list of list of number	Required
declaredAscentUnits	Declared ascent units	number	Required
declaredDescentUnits	Declared descent units	number	Required

Enter nonempty ordered Y-bound pairs and nonnegative declared extents. Return each overflow and any-positive-overflow flag.

upper=max(0,yMax−ascent); lower=max(0,−yMin−descentMagnitude)

Units, indexing, boundary conditions and exceptional cases are defined in the calculation rules above.

Output field	Meaning	Value type
glyphAscentOverflowUnits	Glyph ascent overflow units	list of number
glyphDescentOverflowUnits	Glyph descent overflow units	list of number
anyVerticalExtentOverflow	Any vertical extent overflow	boolean

json

{
  "input": {
    "glyphYBoundsUnits": [
      [
        -200,
        700
      ],
      [
        -250,
        800
      ]
    ],
    "declaredAscentUnits": 750,
    "declaredDescentUnits": 200
  },
  "output": {
    "glyphAscentOverflowUnits": [
      0,
      50
    ],
    "glyphDescentOverflowUnits": [
      0,
      50
    ],
    "anyVerticalExtentOverflow": true
  }
}

Limitations and assumptions

No clipping, font-table truth or line-layout behavior is guaranteed.

Numeric inputs, where present, must be finite. Follow the calculation-specific rules for overflow, underflow and exceptional cases. Matrices are limited to 128 rows and 128 entries per row. Numeric lists are limited to 10,000 entries; string lists to 128 strings of at most 128 characters each. The rules above may impose smaller limits. Missing required fields, extra fields, wrong value types and violations of the calculation rules are input errors. A successfully returned false flag is an evaluated outcome; its meaning is explained above.

Alternative or Complementary methods

Use x-Height Ratio From Font File: A font’s x-height ratio relates a native metric to units per em. Missing native metrics should be represented separately from measured outline height. For a complementary task, use Oldstyle Figure Alignment Checker: Oldstyle-figure evidence can include descenders and varied tops. Observed geometry alone cannot verify an activated font feature.

References

Ascender/Descender Extents Checker — tool.io

Similar or alternative tools

x-Height Ratio From Font File
A font’s x-height ratio relates a native metric to units per em. Missing native metrics should be represented separately from measured outline height.
Oldstyle Figure Alignment Checker
Oldstyle-figure evidence can include descenders and varied tops. Observed geometry alone cannot verify an activated font feature.