This is part of a series of small exercises and experiments I am doing in Houdinis VEX language. There might be better ways to solve this and if I discover a better way I will update the post.
While building a city in Houidini I needed to place some electrical wires along the roads. In order for the wire placements to look a bit more chaotic I needed to break up the curve into smaller sections.
This is done by looping through the curve vertices and create a new prim (poly line) with a random ratio. If a prim only have 1 vertice then it is deleted. All vertices are deleted from the curve and new ones created for the new curves in the process.
//break the primitives into shorter lines
//each prim will only contain 2 vertices (option) limitVerts
for (int i = 0; i<@numprim; i++) {
int numVerticies = primvertexcount(0, i);
int vtxPrim = i;
int lastPrimVtxCount = 0;
int lastPointNum = 0;
for (int j = 0; j <numVerticies; j++) {
//store vertex point & prim
int vtxNum = primvertices(0, i)[j];
int vtxPoint = vertexpoint(0, vtxNum);
//remove the vertex
removevertex(0, vtxNum);
//check if we should start a new prim
if(random(vtxNum) > ch('../breakRatio')) {
vtxPrim = addprim(0, "polyline");
if(lastPrimVtxCount == 1) removepoint(0, lastPointNum); // if the prim only has 1 vert then delete the point
lastPrimVtxCount = 0;
}
//create new vertex for current prim with current point
addvertex(0, vtxPrim, vtxPoint);
lastPointNum = vtxPoint;
lastPrimVtxCount += 1;
}
}
I added a second piece of code that breaks up each segment into a separate primitive, this has nothing to do with the first piece as such but the electrical wires was being exported to Unreal and I need to limit the size of each actor created. Anyway, here’s the code for that part.
//loopp through verts and break up the shit
if(ch('../limitVerts') == 1) {
int numVerts = primvertexcount(0, @primnum);
if(numVerts > 2) {
for(int i = 2; i<numVerts; i++) {
//store vertex points
int vtxNum1 = primvertices(0, @primnum)[i];
int vtxPoint1 = vertexpoint(0, vtxNum1);
int vtxNum2 = primvertices(0, @primnum)[i-1];
int vtxPoint2 = vertexpoint(0, vtxNum2);
//create a new prim and add
int newPrim = addprim(0, "polyline");
addvertex(0, newPrim, vtxPoint1);
addvertex(0, newPrim, vtxPoint2);
}
for(int i = 2; i<numVerts; i++) {
//delete the old extra vertices in a separate loop
int vtxNum = primvertices(0, @primnum)[i];
removevertex(0, vtxNum);
}
}
}