### Propagating point creation with VEX

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Hi folks,

How would you go about adding points in a propagating manner in VEX. Here's what I mean:

- Start with several incoming base points, each with an up vector.

- For each one, add a new point somewhere along its up vector.

- Calculate a new up vector by subtracting base positions from new point positions and setting the new point up vector to the result

- Add the next new point somewhere along the previous point's up vector

So, I called it propagating, because every next point in part defines the following.

I think I'm on the right track here, but my gut's telling me I'm missing something.

```vector up = point(0, "up", @ptnum);
vector currentPos = point(0, "P", @ptnum);
vector newPos = {0,0,0};

int pts[];

for(int i=0; i<@numelem; i++) {
append(pts,i);
}

int iteration = chi("iteration");

for(int j=0; j<=iteration-1; j++){

newPos = currentPos+up;

setpointattrib(0, "up", len(pts)+j, normalize(newPos), "set");
currentPos = point(0, "P", len(pts)+j);
up = normalize(newPos-currentPos);
currentPos = newPos;
}
```

Where do you think I'm wrong here. What would you do? Cheers!

Attachments:
propagating_points.gif (336.7 KB)

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https://hristo.one [hristo.one]
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Some corrections here:

`vector up = @up;vector current_pos = @P;vector new_pos = 0;int samples = chi("samples");float offset = chf("offset");for(int i = 0; i < samples; i++){    new_pos += current_pos + up * offset;    int new_point = addpoint(0, new_pos);        up = normalize(new_pos-current_pos);    setpointattrib(0, "up", new_point, up, "set");        current_pos = point(0, "P", new_point);    }`

I didn't write in the post above, that I intended to later randomize the up vector direction for every new point and thus get a non-linear propagating pattern. I want to achieve a sort of (and I suspect that's not the right term here) parent-child behavior between every point and the next in line (something like tentacles constructed by points propagating in random directions). That's the reason why (in my head at least), calculating a new up by subtracting current_pos from new_pos and setting that at every sample is important.

Except, and this is probably going to seem totally dumb… at sample 2 it falls apart. Up is no longer pointing where I'd expect it to. I bet this has something to do with the last line current_pos = point(0, “P”, new_point);

It appears at sample 2, the up direction is pointing away from the world origin, and not away from the points at sample 1. I feel like I'm missing something so basic…

Edit:
Ok, getting somewhere with random vectors:

Edited by Haki - Dec. 3, 2019 08:23:20

Attachments:
propagating_points_with_rand_dir.jpg (499.3 KB)
rand_dir_propagating_points.hiplc (571.6 KB)
drawing_board_time.jpg (42.2 KB)
propagating_points_with_rand_dir_draw.jpg (269.2 KB)

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https://hristo.one [hristo.one]
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A quick update:

I can't wrap my head around how to gain manual control over the rand vector for each sample yet. Any ideas?

Also, connecting the points in order seems to be a challenge now because of this point number pattern 0,4,5,6…; 1,7,8,9…; 2,10,11,12…

Maybe building arrays for each ptnum. 0(0,4,5,6); 1(1,7,8,9) so on..?
Edited by Haki - Dec. 4, 2019 05:35:45
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https://hristo.one [hristo.one]
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I don't even know where to start to help you, but awesome work until now! Thanks for sharing, will study on!
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Cheers, @demoncase

Ta-da! I got the point arrays exactly in the correct order for the point number pattern I was getting.

Alright, it's going to be smooth sailing from here on… (doing a little dance) Wait, what!? Addprim didn't do what you imagined? Documentation, here I come.

(Edit)
What's the correct way to pass those point number arrays to the addprim function to get a polyline for each one?
Edited by Haki - yesterday 07:19:16

Attachments:
propagating_points_with_rand_dir_prim.jpg (667.3 KB)

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Eureka! (No need for point arrays after all…)

So, from what I originally intended to be a grass generator… it will be a multi-purpose generator (including the effect on hair that electrocution has according to popular cartoon depictions)

Still to figure out a way to control the up angle at every sample… and to orient the points correctly based on the starting points (polyframe the prims I guess…)
Edited by Haki - yesterday 16:05:58

Attachments:
propagating_points_with_rand_dir_prim_eureka.jpg (521.2 KB)

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