Make Curve In VEX

[Igor 2]

How can I make curve in VEX? In Documentation I found spline function but I do not understand how to use. I would like to make smooth blend-curve between many lines.

Thanks!

[konstantin magnus 1,188]

Put all point positions into an array and make parameter "t" slide e.g. from 0 to 1 inside a for loop.

int steps = chi('steps');
vector all_points[];
resize(all_points, npoints(0));

for (int i = 0; i < npoints(0); i++){
    all_points[i] = point(0, "P", i);
}

int prim = addprim(0, "polyline");

for(int i = 0; i < steps; i++){
    float slide = i / float(steps - 1);
    vector pos = spline("catrom", slide, all_points);
    int inter_pt = addpoint(0, pos);
    addvertex(0, prim, inter_pt);   
}

Also a simple function for interpolating 4 points to a curve by yourself would be:

int steps = chi('steps');

vector pt0 = point(0, "P", 0);
vector pt1 = point(0, "P", 1);
vector pt2 = point(0, "P", 2);
vector pt3 = point(0, "P", 3);

int prim = addprim(0, "polyline");

for(int i = 0; i < steps; i++) {

    float slide = i / float(steps - 1);
    vector pos0 = lerp(pt0, pt1, slide);
    vector pos1 = lerp(pt2, pt3, slide);
    vector ipol = lerp(pos0, pos1, slide);

    int inter_pt = addpoint(0, ipol);
    addvertex(0, prim, inter_pt);
}

 

VEX_spline.hipnc

Edited March 17, 2017 by konstantin magnus

[petz 448]

 

On 17.3.2017 at 0:18 AM, Igor said:

I would like to make smooth blend-curve between many lines

 

please take a look at the attached file. it´s an example how you could create bezier curves with arbitrary degree and another one relying on beziers in hermite form since you wrote about blending curves...

petz

curves_vex.hipnc

[Igor 2]

Thank you very much Konstantin and Petz! Your method work perfect!

 

 

[patremblay 2]

Konstantin would it be possible from your setup to include the first and last points as well and also smoothly close the curve?

[konstantin magnus 1,188]

2 hours ago, patremblay said:

include the first and last points as well and also smoothly close the curve?

I dont think the spline()-function does this for cubic splines. You can read about it here: http://www.sidefx.com/docs/houdini/vex/functions/spline.html

But you could connect points to a curve and close it with an add-node and resample this to an 'interpolating curve' or a 'subdivision curve'.

spline.hipnc

Edited August 9, 2018 by konstantin magnus

[patremblay 2]

Thank you, this reminds me to look for simpler solutions first

[tagosaku 3]

Hi, I have an additional question, related to this thread. 

There are random existing curves, for instance. When applying a resample node, it adds points evenly. However, I am looking for a way to add points exponentially then add points with even distance. 

Is that possible to do it procedurally?  

[Librarian 869]

Hope it Helps.

 

PoI ODforce.hipnc

[konstantin magnus 1,188]

Hi @tagosaku,

you can shift points by sampling positions from their respective curves with a channel ramp:

float u = vertexprimindex(0, i@vtxnum) / float(primvertexcount(0, i@primnum) - 1);
v@P = primuv(0, 'P', i@primnum, chramp('shift', u));

 

curve_density.hipnc

Edited April 3, 2020 by konstantin magnus

[tagosaku 3]

Thank you so much, Konstatin M ! That's very smart and primuv seems to be very powerful. I can proceed my stuff from there. 

Tesan, thanks, too. I will use it for different cases in future, too.  

[Noobini 733]

On 4/3/2020 at 6:29 AM, konstantin magnus said:

Hi @tagosaku,

you can shift points by sampling positions from their respective curves with a channel ramp:

float u = vertexprimindex(0, i@vtxnum) / float(primvertexcount(0, i@primnum));
v@P = primuv(0, 'P', i@primnum, chramp('shift', u));

curve_density.hipnc

well this trumps my curveu bias HDA royally !!!