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In QGIS 3.22.1, the Inner Glow effects property (below) creates a sharp outer boundary that fades towards the inside.

enter image description here

I would expect that the Outer Glow effects property (below) would provide the "reverse" of the Inner Glow: a sharp polygon boundary fading to the outside. However, it results in a glow to both(!) sides of the polygon boundary, with no sharp boundary delineation.

enter image description here

How do I create the reverse of the Inner Glow: a sharp boundary that fades to the outside?

I tried using the Inner Glow with negative Spread and Radius, but no joy.

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    This might be a bug actually, I would have expected the same behaviour. Please check on github.com/qgis/QGIS/issues if there is something already and if not, file an issue. Dec 14, 2021 at 22:27
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    Ok, I submitted this bug: github.com/qgis/QGIS/issues/46496
    – Stu Smith
    Dec 15, 2021 at 1:36
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    I actually think this is expected behaviour with 'Outer Glow' applied to the entire polygon and not just the boundary. If the 'Source' layer is of Symbol layer type - Outline: Simple line (rather than some kind of fill), applying Outer Glow does so to the boundary, albeit on both sides. For any kind of sharp boundary with the interior being transparent 'Inverted Polygons' seems to be the intended method/option.
    – she_weeds
    Dec 15, 2021 at 2:48
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    You have a strong argument. However, from docs.qgis.org/3.16/en/docs/user_manual/working_with_vector/… I quote: Outer Glow: This effect is similar to the Inner Glow effect, but it adds the glow effect on the outside of the edges of the feature. The available options for customization are the same as the Inner Glow effect. Emphasis mine.
    – Stu Smith
    Dec 15, 2021 at 6:07

1 Answer 1

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Set layer rendering to Inverted Polygons and Symbol layer type to Shapeburst fill and under Shading style set a distance. Set the second color (here: white) to transparent to see the background:

enter image description here

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  • Yes, this is a correct workaround. Hurray! However, it does not explain the unexpected Outer Glow behavior, for which I've submitted a bug report, as suggested by @bugmenot123.
    – Stu Smith
    Dec 15, 2021 at 1:39
  • I think Shapeburst is the intended way to do what you qant - glow effects are a workaround and not primarily intended for this.
    – Babel
    Dec 15, 2021 at 6:42

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