A Chainlink Fence OSL Shader for Blender Cycles

A simple shader to generate a chain link fence pattern that shows that a little displacement can go a long way.

The example image was again generated using one of Bob Groothuis excellent HDRI maps from his Dutch Skies collection. The concrete texture in the front is from www.cgtextures.com

The whole trick in generating a chain link fence pattern is realizing there is a lot of symmetry involved so we only need to think about the calculations for one part.

#include "stdosl.h"

float arc(float x){ return sqrt(1-(x-0.5)*(x-0.5)/0.25); }

shader chainlink(
 point Pos = P,
 float Width = 0.05,
 output float Fac = 0,
 output float Displ = 0
){
 float x = mod(Pos[0],1);
 float y = mod(Pos[1],1);
    float ox = x ;
    float oy = y ;
    x += Width * (0.5 - oy );
    y -= Width * (ox - 0.5 );
 if ( y > 0.5 ){
  y = 1 - y;
  x = 1 - x;
 }
 if ( x > 0.5 ){
        if ( y > 0.5 - Width ){
   Fac = 1;
   Displ = arc((y-(0.5-Width))/Width);
  }else if (x < 0.5 + Width) {
   Fac = 1;
   Displ = arc((x-0.5)/Width);
  }
 }else{
  float r = hypot(x-0.5,y-0.5);
  if (r < Width) {
   Fac = 1;
   Displ = arc(r/Width);
  }
 }
}

The symmetry trick is in lines 17 - 20 where we invert the right half of a square around the center. The way we generate our pattern would cause the ends of the wires at the edges of the square not to line up so in line 15 an 16 we skew the grid a bit to correct this. this extra work before hand makes generating the wires of the chain link fence now very straight forward,

Example node setup

The way to use this shader is by using a default (aka reset) uv map from a simple plane and scale/rotate it as you see fit. The node setup shown here is about the simplest you can get: we simply map the Fac socket to a mix shader to map between a fully transparent shader and a material, in this cas a node group that implements some simple rather dull metal (not shown here). The caclculated displacement is directly plugged into the material output node and thereby converted to a surface normal but we could have used a bump node as well.

Note that although hardly visible in the ambient lighting of the example image, our material does cast nice shadows.