Erase Blend mode bug when masking

[chrishoward 3]

When I set an object inside another as a mask and then set the inner object to Erase blend mode, the primary object shows a hairline outline. See attached example files and screenshot.

I am on a Mac using Affinity Designer 1.7.1.

This happens in any document.

It does not show when exporting to bitmap formats and not in all cases exporting to vector formats (SVG, PDF, EPS)

This is my first time using the Erase blend mode, so do not know if the bug previously existed.

Thanks

Erase bug.afdesign

Erase bug.svg

Edited August 4 by chrishoward
Clarified attachments

[Hangman 77]

Hi chrishoward,

The difference between your first 'three-layered' shape on the left and the three examples on the right is the layer order for your shapes. If you place the shape with the Erase Blending Mode above the shape you are trying to erase (see attached) and as per your sample on the left then this removes the hairline.

I'm not offering this as a 'fix', only a possible workaround as I'm unsure whether the hairlines are expected behaviour when creating the artwork in the way you have but I suspect the hairlines are appearing because applying blending modes has the effect of rasterising the image, not that this should matter.

Hopefully someone from the Affinity team can comment though regarding the reason this happens.

Erase bug.afdesign

[chrishoward 3]

Thanks, Hangman. That is very good alternative, and probably how most people do it. Which is probably why this bug hasn't shown up before.

[Hangman 77]

Depending on what your objective is with the shapes, you could use the Subtract Geometry option in place of the Erase Blend Mode, this would have the benefit of not rasterising the shapes on export to svg, pdf and eps but it will merge the layers to become a single layer which may or may not be important for you.

 

[Alfred 4,262]

9 minutes ago, Hangman said:

the Subtract Geometry option ... will merge the layers to become a single layer

You can prevent that by holding down Option/Alt while you click on the ‘Subtract’ button. This will give you a compound layer/object where the original shapes are retained.

[Hangman 77]

You learn something new every day... so that's how you do that, I'd seen the icons in the layers panel before but hadn't realised how they got there. So that's a much better way to create this, maintaining the vector format on export and providing complete flexibility by allowing the shapes to be moved and scaled after creating the compound path.

Thanks Alfred for today's lesson...

[chrishoward 3]

Thanks, Hangman. The Subtract is probably the way I should have done it! It's the way I have been doing things. I think I'd seen the Erase blend mode and was just looking for reason to use it, so overlooked that.

Nice tip, Alfred. Thanks.

P.S. Affinity dudes, despite the alternative ways Hangman has shown of achieving this, my original way still appears to demonstrate a bug.

[MEB 7,389]

Hi chrishoward,
Welcome to Affinity Forums
This is not bug or object order issue. It's happening because those objects are clipped inside other objects.The blend mode is irrelevant - If you set the colour of the clipped object to white and the clipping object to black (or other contrasting colours) with the blend mode set to normal on both you will also see those "issues". Go to Affinity Preferences, Performance section and tick Use precise clipping to get a more accurate rendition of clipped objects (no hairlines).

[chrishoward 3]

Thanks heaps, MEB.

I would suggest tho that that then presents a UX problem.

It should be easier to know the fix for this problem (maybe the option should also be in the View Mode menu), and the Export panels should include a toggle to turn on precise clipping. 

 

[MEB 7,389]

Hi chrishoward,
It's not a UX issue. The export always uses precise clipping no matter its enabled or not in the preferences. This is an option in the Performance section because it affects screen rendering performance a little if you are working with a complex illustration with various clipped objects - so we keep it disabled by default.
 

[chrishoward 3]

Thanks, MEB.

Not sure about that. As my original post says, the problem is evident in exported vectors types - PDF, SVG, EPS. And I attached an SVG as proof.

And I just exported to a PDF with the "Use precise clipping" enabled and it still has the issue in the PDF - just like the SVG above. See attached.

However, in both cases, it's only evident on a circular object. As my original image says "Third example shows in export to vector formats SVG, EPS, PDF, but other two do not."

And i tried doing  300dpi PDF too.

It's quite reasonable for "Use precise clipping" to be in Performance settings but it's equally reasonable for it to also be in View Mode menu since it affects the view. Kinda of like InDesign and it's three different view quality modes.

My own opinion is if something looks like a bug but has a fix that's not easily determined by ye average user - such that one logs a forum request reporting it as a bug - then there's probably user experience issue.

My user experience was I spent well over 30 mins testing and proving this "problem" that could have been averted by better UX design. As well, I spent time googling and searching for an answer. My user experience may have been much, much better with a simple option in the View Mode. (Can't absolutely say i would have quickly found it there, but definitely more chance of it being both visible and meaningful if i saw it there)

 

Erase bug.pdf

[MEB 7,389]

Sorry, I missed the export issue for vector objects (this is a different case). I'm logging these to be looked at.