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If I understand it right, Accumulate Field node works in the order of indices. Is there a way to reassign/change order of indices in Geometry Nodes or change the order of field accumulation?

Fedor Petrov
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  • The node Accumulate Field accumulates the passed values, and can even do this in groups. So it always depends only on the input. What exactly would be your goal? Can you describe it a little bit more? – quellenform May 12 '22 at 17:49
  • Yes. But how do I setup which value is first, which value is second, which value is third etc It takes the order from the index either of points or vertices etc.... For example I have a random Distribution of points on faces on some surface. Let's say I want in one case to start my field accumulation from the left (i.e. from the smallest x values to the largest) in another case from the right (i.e. from the largest x values tp the lowest). – Fedor Petrov May 12 '22 at 18:07
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    OK, I see. This is a bit complicated with the current tools. Unfortunately, there is no possibility of sorting (or loops), except via a self-created logic from nodes. And this is very individual, that's why I ask for a concrete example. – quellenform May 12 '22 at 18:13
  • I think it`'s not possible right now dynamically. There is for example a kind of functionality in Blender Edit Mode -> Mesh -> Sort Elements ->. It's often used together with build modifier. It also has observable effect on Field Accumulation order. But dynamically seems to be impossible. – Fedor Petrov May 12 '22 at 18:16
  • The example is exactly to have a kind of controlled brownian motion. I have particles distributed on a surface, I want to accumulate their position and build kind of lightning, but want to control with maybe empty and proximity control which particles coordinates are taken first for the accumulation. – Fedor Petrov May 12 '22 at 18:19
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    Maybe this could be of some help https://blender.stackexchange.com/questions/260218/sort-points-by-distance-from-object-expanded-sort-any-field – jst kiko May 12 '22 at 18:39
  • Thanks @jstkiko I already started myself thinking in similar direction. Maybe it ll work. – Fedor Petrov May 12 '22 at 18:47

1 Answers1

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In this particular case (Accumulate Field) you can use the "Field at Index" node to change the order of accumulation.

Lets say we want to add up the X position values: Accumulate X position of vertices in index order

We can change the order by inserting a "Field at Index" node. Here I'm using N-i to invert the index: Accumulate X position with an inverted index

lukas_t
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