Description
Compare paired supplied primary/fallback glyph advances and total run shift; caller must establish glyph correspondence, no shaping equivalence.
A glyph’s advance moves the next placement origin; its ink box describes visible bounds relative to that origin. Ink can overhang the advance, and an unknown box differs from a known empty box. These tools use caller-supplied glyph IDs and metrics, placing a horizontal run by cumulative advances without shaping text.
Compare paired supplied primary/fallback glyph advances and total run shift; caller must establish glyph correspondence, no shaping equivalence.
When to use this tool
Use this tool to compare paired supplied primary/fallback glyph advances and total run shift; caller must establish glyph correspondence, no shaping equivalence.
How to use the tool and how it works
- Enter primary, fallback using the input definitions below.
- Run the operation. Resolve malformed-input errors before interpreting the result.
- Read result.deltas, result.totalDelta. Interpret signs, units, ordering and null values using the rules below.
Require aligned primary/fallback lists. For each index return fallback advance minus primary advance; totalDelta is the sum of fallback advances minus the sum of primary advances.1
| Input field | Meaning and units | Accepted input |
|---|---|---|
| primary | Primary advances aligned by glyph correspondence with fallback. | Dense list of at most 128 finite numbers, subject to the stated integer/shape rules. |
| fallback | Fallback advances in the same units and order as primary. | Dense list of at most 128 finite numbers, subject to the stated integer/shape rules. |
| Output field | Interpretation |
|---|---|
| result | Object containing the fields below. |
| result.deltas | Fallback minus primary advance at each aligned input index. |
| result.totalDelta | Fallback run advance minus primary run advance. |
{
"input": {
"primary": [
4,
5
],
"fallback": [
5,
3
]
},
"output": {
"result": {
"deltas": [
1,
-2
],
"totalDelta": -1
}
}
}Limitations and assumptions
- The caller must establish correspondence and common units; equal run length does not establish equivalent glyph shaping.
- All advances, box coordinates, shifts and positional tolerances must share caller-defined metric units. Signed advances are accepted. Glyph records contain id, advance, integer cluster 0–8192 and box = null or [minX,minY,maxX,maxY] with ordered bounds.
- Every declared top-level input is required and unknown fields are rejected. Ordinary strings are limited to 8,192 UTF-16 code units and lists to 128 entries, with tighter operation-specific bounds where stated. JSON text has bounded nesting and node counts.
- Numeric outputs must be finite and within the absolute safe-integer magnitude; exact larger integers use decimal text. Source positions are zero-based UTF-16 offsets and span ends are exclusive unless a different convention is explicitly stated.
Alternative or Complementary methods
Obtain metrics and cluster mappings from the intended font/shaping system, then inspect the supplied observations. Use actual rendering when hinting, fallback choice or visible pixel extents matter.
References
Similar or alternative tools
- Glyph Advance Run Tab Stop Placement
Place glyph-run tab positions at the next strictly greater explicit stop, then repeat a supplied positive interval after the last stop; no text shaping.
- Glyph Advance Scale Transform
Scale explicit glyph advances and known box coordinates by a nonnegative uniform factor; no hinted rasterization or font metric inference.