Re: [csswg-drafts] [filter-effects-2] Progressive blur via `linear-blur()` (#13285)

I just realized that there's a possible ambiguity in my proposed syntax. A value of `0` as first value could either be interpreted as the first blur radius or the angle of the progressive blur.
Though the [definition of `<angle>` values has this note](https://drafts.csswg.org/css-values-4/#angles:~:text=For%20legacy%20reasons%2C%20some%20uses%20of%20%3Cangle%3E%20allow%20a%20bare%200):

> Note: For legacy reasons, some uses of `<angle>` allow a bare `0` to mean `0deg`. This is not true in general, however, and will not occur in future uses of the `<angle>` type.

So we should be fine here and it should be interpreted as `<length>` value in that case.

Also note that the alignment with the `linear-gradient()` syntax means that a single blur value is allowed. I.e. `linear-blur(10px)` would be valid and be equivalent to `blur(10px)`.

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I imagine implementations might need to approximate the rendering by splitting the blurs into several steps instead of doing a fully smooth transition.

@grorg @chrishtr As implementers and editors of the spec, maybe you have some input on this idea, especially on feasibility.

Sebastian

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Received on Friday, 2 January 2026 13:43:32 UTC