# Option to "Erase Behind"

**URL:** <https://doubleandthrice.discourse.group/t/option-to-erase-behind/24>\
**Category:** McKinley\
**Created:** [September 8, 2026, 4:19pm UTC](https://doubleandthrice.discourse.group/t/option-to-erase-behind/24 "2026-09-08T16:19:37Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![biscuit](https://yyz2.discourse-cdn.com/flex052/user_avatar/doubleandthrice.discourse.group/biscuit/32/38_2.png) [@biscuit](https://doubleandthrice.discourse.group/u/biscuit)\
**Post date:** [September 8, 2026, 4:19pm UTC](https://doubleandthrice.discourse.group/t/option-to-erase-behind/24/1 "2026-09-08T16:19:37Z")

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Unless I am missing something, there doesn’t appear to be a way to apply the “Erase Behind” option on a layer, which only erases behind the filled parts of the layer. Very useful when you want to overlap layers with some transparency.

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<div class="post-metadata">

**Author:** ![AmyWorrall](https://yyz2.discourse-cdn.com/flex052/user_avatar/doubleandthrice.discourse.group/amyworrall/32/5_2.png) [@AmyWorrall](https://doubleandthrice.discourse.group/u/AmyWorrall)\
**Post date:** [September 18, 2026, 8:09pm UTC](https://doubleandthrice.discourse.group/t/option-to-erase-behind/24/2 "2026-09-18T20:09:13Z")

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You may have found a thing McKinley can’t accurately represent.

McKinley lets you apply colours directly to objects, or to groups of objects via “override children’s colour mode”, or to layers via “composites as one unit”.

For individual objects, McKinley lets you set a fill and/or stroke colour, plus also an optional “knockout” effect. You can get Apple’s erase behaviour in two ways:

- if you _only_ want to erase, then setting a colour of “erase” on your object will do that.
- If you want to erase behind _and_ draw a colour, use a knockout. This enables the erasing behind. A knockout can also have an outset value, which makes the erased area bigger than the coloured area, but if you leave the outset at 0 then the erased area matches the content.

However, that’s only for colouring individual objects. If you’re colouring a whole group or layer, McKinley isn’t currently exposing the knockout option. So the question becomes, whether what you’re trying to do can be represented with knockout on _individual objects_, or whether you need it on e.g. groups as a whole.

The terminology is confusing here, since McKinley’s layers aren’t a direct analogue for SF Symbols’ concept of ‘layers’. Notably, in McKinley you don’t need to use separate layers just to apply separate colours, unlike Apple’s workflow. But sometimes this makes it harder to talk about the equivalents to various things!

If you have a symbol you’ve made already that you’re wondering how you’d accomplish in McKinley, feel free to send it to me and I can take a look!