Variable Row Prefix Offsets
Compute cumulative variable-row boundary offsets, including the terminal boundary and explicit zero-height rows.
Description
Compute cumulative variable-row boundary offsets, including the terminal boundary and explicit zero-height rows.
Prefix offsets turn variable row extents into boundaries suitable for later position lookup.
When to use this tool
Compute cumulative variable-row boundary offsets, including the terminal boundary and explicit zero-height rows.
- Prepare the supplied rowExtents fields for this operation.
- Compare the complete example with the representation used by your own input before carrying the result into another step.
How to use the tool and how it works
- Enter rowExtents. Use the exact text syntax, units and index conventions explained below.
- Run the tool. If input validation fails, correct the supplied fields before interpreting any result.
- Read result.boundaryOffsets, result.totalExtent. Interpret false, null and empty lists using the distinctions below; they can be valid outputs.
Require every rowExtent nonnegative. Begin boundaryOffsets with zero and append each cumulative sum; totalExtent is the final sum.1
| Input field | Meaning and representation | Accepted input |
|---|---|---|
| rowExtents | row extents. | List of finite numbers; bounded by the operation |
| Output field | Interpretation |
|---|---|
| result | Object containing the named outputs below. |
| result.boundaryOffsets | The boundary offsets list in the ordering and representation described above. |
| result.totalExtent | The total extent value under the stated formula or text convention. |
{
"input": {
"rowExtents": [
10,
20
]
},
"output": {
"result": {
"boundaryOffsets": [
0,
10,
30
],
"totalExtent": 30
}
}
}Limitations and assumptions
- Zero-height rows create duplicate boundaries. No gaps, borders, virtualized DOM state or scroll position is inferred.
- Rectangle arrays use [x,y,width,height] with nonnegative extents. All dimensions must use the same coordinate frame and unit; values are supplied rather than measured from a page.
- Every declared top-level field is required and unexpected fields are rejected. Numeric inputs must be finite; ordinary text fields are bounded to 8,192 UTF-16 code units, with tighter operation-specific limits where stated.
- String lists have at most 128 entries of at most 128 code units; matrices have at most 128 rows and columns. Larger numeric lists and parsed JSON have separate bounded budgets. Nonfinite results and excessively large serialized outputs are rejected.
- Indexes are zero-based and spans have an exclusive end unless explicitly stated otherwise. A valid false, null or empty-list result is distinct from malformed input.
Alternative or Complementary methods
Measure the actual layout when browser behavior matters. The formulas use supplied coordinates and explicit simplifications; they do not account for every box, writing mode, clipping ancestor or simultaneous layout change.
References
Similar or alternative tools
- Variable Row Visible Index Range
Plan visible indexes for explicit positive variable row extents; retain an empty result rather than infer estimated heights.
- Fixed Row Visible Index Range
Plan half-open visible fixed-row indexes with positive geometric intersection; exact end contacts are excluded and empty viewports contain no rows.