Add antialiasing to triangles in MarkerVisualisation

[EVAST9919]

Closes #34243

2025-07-18.12-30-25.mp4

[peppy]

Looking good.

Do you think we should also apply to the top timeline?

There's no movement on these ones but they are quite sharp visually.

[bdach]

I guess I'm not supposed to come into PRs like this anymore but this is the hackiest code I've seen in a hot minute. how does this even work? why is it reusing the shader for the bordered triangles for this? what is half the code in this PR doing? is someone going to realise that touching the bordered triangles shader potentially will break the appearance of editor now? why aren't framework triangle primitives getting AA instead? I have so many questions

[EVAST9919]

why aren't framework triangle primitives getting AA instead?

Framework triangles don't support antialiasing. But once you said that - I realised we can use boxes rotated by 45 degrees. Though we would still need a custom draw node to add ability to elongate them properly depending on the use case, but we can avoid shader usage

[peppy]

I get the code quality concerns but with something this local I'm personally willing to turn a blind eye to get-things-done (used in one place, private class, shader it's using is probably not going to change/break).

The box version does sound better if we can avoid some faff, but I don't want this to become a huge task, was just hoping for a quick 15 minute fix.

[EVAST9919]

The box version does sound better if we can avoid some faff, but I don't want this to become a huge task, was just hoping for a quick 15 minute fix.

It's okay, not a huge task. I've made adjustments to avoid shader usage