SVG filterUnits Attribute
filterUnits determines whether a filter element's bounding region coordinates are relative to the element's bounding box or user space.
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objectBoundingBox vs userSpaceOnUse
filterUnits defaults to objectBoundingBox, meaning the filter's x, y, width, and height values are fractions of the filtered element's bounding box, while setting filterUnits to userSpaceOnUse instead interprets those same values as absolute coordinates in the current user coordinate system, unaffected by the element's own size.
- The default objectBoundingBox treats x/y/width/height as bounding-box fractions
- userSpaceOnUse instead treats those values as absolute user-space coordinates
- Switching modes changes how much extra filter region surrounds an element
Why the Filter Region Sometimes Clips Effects
A filter's default region only extends 10% beyond the element's bounding box in each direction, which is often too tight for effects like large blurs or offset shadows, causing visible clipping — widening x, y, width, and height (in whichever unit mode filterUnits specifies) fixes this clipping without changing the visual effect itself.
- The default filter region extends only 10% beyond the bounding box
- Large blurs or offset shadows can get visibly clipped at this default edge
- Widening x/y/width/height in the correct unit mode fixes the clipping
Frequently Asked Questions
Why is my blur or shadow getting cut off at the edges?
The filter region defaults to only 10% beyond the element's bounding box, so wide blurs or shadow offsets often exceed that region and get clipped — widen x/y/width/height to fix it.
Should I use objectBoundingBox or userSpaceOnUse for filterUnits?
Use the default objectBoundingBox for filters meant to scale with the element, and userSpaceOnUse when you need a fixed-size filter region independent of the element's own dimensions.
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