Fractal Terrains' Overlays

BlackYeti

Hello. I'm new here, but I was hoping I could ask about a problem I'm having with an overlay.

This is the world I'm working on with two different overlays displaying. The first is a simple tectonic map which is working fine. The second, though, is supposed to be marking the equator, the tropics, and the polar circles (calculated for an ~12° axial tilt), yet as you can see, the southern tropic and northern polar circle aren't displaying here.

However, when I zoom out, the missing lines reappear but the equator disappears.

Whenever I try zooming in or out, or simply pan around the map, it seems to inevitably cause the lines to pop in and out of existence at random.

Does anyone know why this is happening, or more importantly, how to stop it?

Thanks in advance.

jslayton

Your image is a higher resolution than ft is showing, resulting in what's called aliasing. Ft doesn't try to do any filtering on the input images to try to match the sample resolution to the displayed resolution (which would require the whole mip pyramid).

Unfortunately, the intended use case for image overlays was solid-color images rather than line art.

BlackYeti

Well, that's a depressingly obvious reason for it to happen in hindsight; consider me suitably ashamed for having not considered it. At least it makes it very simple to fix. ?

Thanks ever so much for taking the time to explain it: it's really helpful.

Loopysue

It's not really that obvious, BlackYeti :)

I didn't know either.

BlackYeti

But that's the thing about hindsight: it's a very good lens to retroactively make things appear obvious. Especially, as in this case, when you already have some limited understanding of the priciple involved (not to imply that you don't know about aliasing – I don't know what you don't know – just trying to illustrate where I'm coming from).

That said, I do take your point. I'm probably just being overly critical of myself, as usual. ?

MarkOlsen

Since the problem as identified by @jslayton is the anti-aliasing, I wonder if redoing your overlay image with much thicker lines would solve the issue?

BlackYeti

That is a very good suggestion. It was actually the first thing I tried after reading jslayton's response and it worked ?. In fact, the lines only needed to be a little thicker, I only increased them a tiny amount.

Maybe I should have made it clearer that I had already fixed it, but either way, thanks for the suggestion.