Layer mask (alpha)

[ryan-de-boer]

I'd like to be able to create a special layer for an existing layer to paint black to white colors on it to represent transparency of the layer. The simplest I've seen so far is Krita's feature where you just right click a layer and select Add, Add Transparency Mask. Perfect. Affinity is meant to support it but I can't get it working correctly there (maybe they made it a bit difficult to use).

I've found some paint dot net plugins that sound like they can do it.
This one is even open source:
https://forums.getpaint.net/topic/1854-alpha-mask-import-plugin-20/
I haven't tried it, because I want a Pinta plugin or default feature :)

What would be wonderful is for example you to use an eraser on a layer and that can add shades of black to the mask instead of destroying the layer. It just would be nice to see the layer effect while you are modifying its mask. I checked in Krita and it has this feature! You just have the layer visible and the mask selected - then painting the mask shows you the total effect. So simple and cool. But you can just do something really simple first.

I'm a programmer, so I may have a try at it if noone wants to.

[ryan-de-boer]

I found a similar discussion here: #1355
But unfortunately he specifically says he does not like Krita's implementation :(
He would rather "Photoshop-Medibang Paint style and not like Krita". But I really like Krita's implementation!
Maybe do it like photoshop then, as thats what most people will be used to? Hopefully I don't find it too difficult compared to Krita.

I found a video of what it works like in Photoshop:
How to use Layer Masks in Photoshop | Adobe Tutorial
https://www.youtube.com/watch?v=fzBFTEKQ4ro
It shows a lot of features though, maybe just implement the first part of the video and not the advanced hair fixing part.

[ryan-de-boer]

I worked out how to do it in Affinity. You select the layer, and then click the "Mask Layer" button in the bottom of the layers section. Then it creates the mask tied to the layer. You can have the layer visible and select the mask layer and then you can paint on it just like Krita. I found a youtube video showing how.
Here's the one that taught me how to use the feature:
https://www.youtube.com/watch?v=lOc6TpFTIuU

[ryan-de-boer]

Depends on this feature to allow smooth brushes:
#1984

[ryan-de-boer]

Managed to implement smooth brushes (and smooth stamp). But smooth brush should be good enough to use with the mask layer feature.

[ryan-de-boer]

I've made good progress on having a layer mask alpha. Here is a video showing how much I have done:
https://github.com/ryan-de-boer/ryan-de-boer.github.io/raw/refs/heads/main/2026-02-16%2023-19-16.mp4
Done: save/load, preview icon
Todo: history, clean up code, copy and paste mask, remove mask, (also moving layers would help #1998)