melting.md

Step one, download "gregs-large.stl" from https://www.thingiverse.com/thing:6713/files and convert it into OBJ format and read it into AngelCAD, and "melt" it

AngelCAD language reference https://arnholm.github.io/angelcad-docs/docs/annotated.html

// AngelCAD code.

shape@ main_shape()
{
   auto@ p = polyhedron("gregs-large.obj");

   // traverse the vertices
   double factor = 0.025;
   for(uint i=0; i<p.nvert(); i++) {
   
      // get position of this vertex
      pos3d@ vtx = p.vertex(i);
      double t   = vtx.x();
      if(t > 0.0) {
      
         // transform vertex by rotation
         double angle = factor*t*PI/4;
         @vtx = rotate_y(rad:angle)*vtx;
         p.set_vertex(i,vtx);
      }
   }

   return p;
}

void main()
{
   shape@ obj = main_shape();
   obj.write_xcsg(GetInputFullPath(),secant_tolerance:-1.0);
}

This works in principle, but the result is ugly due to the coarse mesh:

melting1.stl

melting2.md

Step two, we remesh the file to have 4mm sized triangles so that "melting" will work better

$ polyfix gregs-large.stl gregs-large_remesh.obj -remesh=4 -dtol=1E-6

Then perform the same operation on the remeshed file.

// AngelCAD code.

shape@ main_shape()
{
   auto@ p = polyhedron("gregs-large_remesh.obj");

   // traverse the vertices
   double factor = 0.025;
   for(uint i=0; i<p.nvert(); i++) {
   
      // get position of this vertex
      pos3d@ vtx = p.vertex(i);
      double t   = vtx.x();
      if(t > 0.0) {
      
         // transform vertex by rotation
         double angle = factor*t*PI/4;
         @vtx = rotate_y(rad:angle)*vtx;
         p.set_vertex(i,vtx);
      }
   }

   return p;
}

void main()
{
   shape@ obj = main_shape();
   obj.write_xcsg(GetInputFullPath(),secant_tolerance:-1.0);
}

This time, the result is as we want:

melting2.stl