Mask editor anti-aliasing at max hardness

[avc]

Prerequisites

• I am running the latest version of ComfyUI
• I have searched existing issues to make sure this isn't a duplicate
• I have tested with all custom nodes disabled (see how)

What happened?

The Mask Editor | Image Canvas mask tool at max hardness is still anti-aliasing, causing fills to have a border next to the painted outline.

I think this bug appeared after image editing was introduced to the mask editor. Prior to that, mask tool at max hardness was 100% binary, i.e., had jagged pixel edges without any fractional opacity.

Steps to Reproduce

1. Add a Load Image node.
2. Select or upload an image.
3. Right click image > Open in Mask Editor | Image Canvas
4. With the mask tool selected, set opacity to 100%, hardness to 100%, smoothing precision to 10% or more.
5. With the mask tool, draw a closed shape, e.g. an oval.
6. Select the fill tool and click in the area enclosed by the shape.

How is this affecting you?

Feature doesn't work as expected

ComfyUI Frontend Version

1.25.11

Browser

Other

Console Errors

Logs

Additional Context

Mac OS 15.6.1, Mac Mini M4

┆Issue is synchronized with this Notion page by Unito

[dosubot]

Hi @avc! I'm Dosu and I’m helping the ComfyUI_frontend team.

You're right—this is a regression. The current Mask Editor always draws brush strokes using a radial gradient, even at max hardness. While the gradient stops are set to fully opaque at both ends when hardness is 1, browser rendering of gradients still introduces several pixels of anti-aliasing, which prevents truly binary mask edges and creates the visible fringe you described. The previous implementation used solid fills for the brush at max hardness, resulting in hard, aliased edges except for unavoidable single-pixel smoothing at subpixel boundaries. This change likely happened during the refactor that added image editing features and unified the brush logic. To restore true binary mask edges at max hardness, the drawing logic would need to conditionally use a solid arc or rect with constant alpha, as in the old code. See code details.

To reply, just mention @dosu.

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[christian-byrne]

Hey @brucew4yn3rp, this seems related to your recent work in #4519 on brush hardness rendering!

Wonder if there's a similar hardness handling issue in the fill tool logic that might need the same treatment? WDYT - could be worth checking if the fill operation is respecting the hardness parameter properly.

[brucew4yn3rp]

Thanks @avc and @christian-byrne. This should be resolved with the latest push in #4519

When hardness was set to 1, the canvas was correctly using a radial gradient with identical color stops at both ends, but browsers still applied anti-aliasing to the gradient rendering itself, creating jagged edges even though the gradient mathematically represented a hard edge - so I switched to solid fills at max hardness.

[christian-byrne]

Resolved in #4519. Please re-open if you experience the issue again. Thanks @brucew4yn3rp !