thin lines between objects that have supposedly been snapped together

Quote from sadrobot

I am trying to make a tessellation using a grid of rectangles, snapped together, although the tessellation itself is composed of white and yellow triangles rather than rectangles. Each triangle spans across two rectangles. The problem I am having is that, if there is a dark background, where the two rectangles join, a dark line is visible, even though the two rectangles have been snapped together and therefore there should be nothing in between them. Sometimes the line disappears when I zoom right in, but appears when I zoom out. The behaviour is a bit inconsistent.

I've tried resizing the rectangles to whole numbers of pixels. I've tried increasing the resolution of the design in AF Photo. Nothing seems to work.

How can I get rid of these lines/gaps?

The way you've put it, you're saying everything and nothing at the same time—we don't know how you created these triangles;
do they have a stroke?
are they vectors, or have they been converted to curves?
a screenshot of the situation, including the Layers panel, would be helpful;
are you working on Mac or Windows?
Basically, give us as much information as possible so we don't have to guess (it's too hot for that)...

You would also have to check, and possibly experiment, in the snapping options. The less are selected, the easiest it is to achieve the expected result.

You could also consider the possibility to use a triangular or oblique grid (Mode > Advanced). Note that you can edit the grid presets.

This is a display error caused by the design of the monitor panels.

Monitors can only display integer pixels. As a result, sub-pixel gaps may appear at zoom levels < or > 100%.

It may help to set Retina Rendering to “High Quality (Slowest)” in Affinity's performance settings.

Exporting a Triangle to a PNG is never going to give a sharp edge. Pixels (which are what make up a PNG) are square, triangles don't have square edges. This is an antialiasing problem.

So if you have to export to PNG then off the top of my head all I can suggest is to set the Layers to use Force off in the Antialiasing section of the Blend Options.

This is with it set to Inherit

And here it is with it set to Force Off

Quote from sadrobot

Surely if that was the case then the lines shouldn't be there when I export the design as a PNG? Unfortunately they are visible in the PNG.

This information should have been included in the original post.

Well, without knowing the composition of the image, it's hard to come up with a solution.

Quote from sadrobot

Surely if that was the case then the lines shouldn't be there when I export the design as a PNG? Unfortunately they are visible in the PNG.

It might help if you could post an example PNG file showing what you mean by thin lines & the Affinity file you created it from. Please try to keep this as small & simple as possible.

Quote from sadrobot

This is what I mean, except for the three thicker lines on the 4th, 5th and 6th rows, which are caused by something else.

That is a JPEG , not PNG file, so it is almost certainly showing antialiasing artifacts.

And you did not include the Affinity file it was exported as a PNG from so there is very little we can tell about the cause.

For such a case, the best way to post attachments here is to zip all the files (PNG + Affinity). Otherwise, the forum engine can modify the image.

Also, do you need to do this in Photo? At first sight, a vectorial file looks more appropriate.