Scroll Progress from Extents
Compute normalized scroll progress from explicit extents; a non-scrollable viewport has defined zero progress.
Description
Compute normalized scroll progress from explicit extents; a non-scrollable viewport has defined zero progress.
Scroll progress is a fraction of maximum scroll distance. Nonoverflowing content needs an explicit zero convention.
When to use this tool
Compute normalized scroll progress from explicit extents; a non-scrollable viewport has defined zero progress.
- Prepare the supplied scrollPosition, contentExtent, viewportExtent 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 scrollPosition, contentExtent, viewportExtent. 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.progress, result.maximumScroll. Interpret false, null and empty lists using the distinctions below; they can be valid outputs.
Compute maximumScroll=max(0,contentExtent-viewportExtent), require scrollPosition within it and return position/maximum or zero when maximum is zero.1
| Input field | Meaning and representation | Accepted input |
|---|---|---|
| scrollPosition | scroll position. | Finite number |
| contentExtent | content extent. | Finite number; zero or greater |
| viewportExtent | viewport extent. | Finite number; zero or greater |
| Output field | Interpretation |
|---|---|
| result | Object containing the named outputs below. |
| result.progress | The progress value under the stated formula or text convention. |
| result.maximumScroll | The maximum scroll value under the stated formula or text convention. |
{
"input": {
"scrollPosition": 25,
"contentExtent": 200,
"viewportExtent": 100
},
"output": {
"result": {
"progress": 0.25,
"maximumScroll": 100
}
}
}Limitations and assumptions
- No DOM scroll range, overscroll, reversed axis or RTL convention 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
- Scroll Position from Progress
Invert normalized scroll progress into a position using explicit content/viewport extents.
- Rectangle Scroll Reveal Delta
Plan minimum-edge scroll reveal deltas in axis-aligned coordinates, prioritizing the leading edge when an item exceeds viewport size; no DOM scrolling occurs.