Edge divide in vex?

[TomRaynor]

Is there any way to split a polygon down the middle using vex and something like an attribwrangle in the same way that an edgedivide SOP works?

 

Thanks.

edgeDivideInVex.hip

[iamyog]

Could be a lead but according to jlait: "it wouldn't be fun or easy"

https://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&p=138661#138661

Edited November 10, 2014 by iamyog

[konstantin magnus]

i thought about this recently, as well. i am probably boring you, but basically cutting a polygon in two is nothing different than redrawing two polygons and deleting the old one.

 

in a four-sided polygon this would mean to create two new points inbetween existing points, and drawing vertices while creating prims. i don't know how to access specific point positions in vex, but at least some functions in my example might be useful.

// CALCULATE AVERAGE POSITIONS

vector avpos_0 = ((point_0 + point_1) /2);
vector avpos_1 = ((point_2 + point_3) /2);


// CREATE INBETWEEN POINTS

int pt_4 = addpoint(geoself(), set(avpos_0));
int pt_5 = addpoint(geoself(), set(avpos_1));

// CREATE FIRST PRIMITIVE

int prim1 = addprim(geoself(), "poly");

addvertex(geoself(), prim1, point_0);
addvertex(geoself(), prim1, pt_4);
addvertex(geoself(), prim1, pt_5);
addvertex(geoself(), prim1, point_3);


// CREATE SECOND PRIMITIVE

int prim2 = addprim(geoself(), "poly");

addvertex(geoself(), prim2, pt_4);
addvertex(geoself(), prim2, point_1);
addvertex(geoself(), prim2, point_2);
addvertex(geoself(), prim2, pt_5);



// DELETE ORIGINAL PRIM

removeprim(int geoself(), prim0, int andpoints); 

Edited November 11, 2014 by konstantin magnus

[konstantin magnus]

half-edges might be useful in a more complex situation:

http://www.sidefx.com/docs/houdini13.0/vex/halfedges

[edward]

Yes, it gets more complicated quickly. For example, splitting a polygon that has a shared edge with one (or more) other polygons. Then you also have to consider the case where you want attributes interpolated along the edges into the new points.

[magneto]

Does this mean we won't see this feature in VEX? It does seem a lot of work to do it by hand each time. Houdini can already do this in the HDK, right?

[edward]

Yes, it can of course be done in the HDK but I don't think that was the original question.

[magneto]

Yes, it can of course be done in the HDK but I don't think that was the original question.

Thanks Edward. I mentioned that because if it's in the hdk, you guys can expose this function to VEX saving us the trouble of doing it manually.

[konstantin magnus]

this (russian) tutorial explains how to cut edges in vex: