ribbon.vert Example File

  #version 330 core

  in vec3 vertexPosition;
  in vec3 vertexNormal;

  out EyeSpaceVertex {
      vec3 position;
      vec3 normal;
  } vs_out;

  uniform mat4 modelView;
  uniform mat3 modelViewNormal;
  uniform mat4 mvp;

  uniform float time;
  uniform float amplitude = 1.0;
  uniform float lambda = 20.0;
  uniform float period = 15.0;

  //
  // Description : Array and textureless GLSL 3D simplex noise function.
  //      Author : Ian McEwan, Ashima Arts.
  //  Maintainer : ijm
  //     Lastmod : 20110409 (stegu)
  //     License : Copyright (C) 2011 Ashima Arts. All rights reserved.
  //               Distributed under the MIT License. See LICENSE file.
  //

  vec4 permute( vec4 x )
  {
      return mod(((x*34.0)+1.0)*x, 289.0);
  }

  vec4 taylorInvSqrt( vec4 r )
  {
      return 1.79284291400159 - 0.85373472095314 * r;
  }

  float snoise(vec3 v)
  {
      const vec2  C = vec2(1.0/6.0, 1.0/3.0) ;
      const vec4  D = vec4(0.0, 0.5, 1.0, 2.0);

      // First corner
      vec3 i  = floor(v + dot(v, C.yyy) );
      vec3 x0 =   v - i + dot(i, C.xxx) ;

      // Other corners
      vec3 g = step(x0.yzx, x0.xyz);
      vec3 l = 1.0 - g;
      vec3 i1 = min( g.xyz, l.zxy );
      vec3 i2 = max( g.xyz, l.zxy );

      //  x0 = x0 - 0. + 0.0 * C
      vec3 x1 = x0 - i1 + 1.0 * C.xxx;
      vec3 x2 = x0 - i2 + 2.0 * C.xxx;
      vec3 x3 = x0 - 1. + 3.0 * C.xxx;

      // Permutations
      i = mod(i, 289.0 );
      vec4 p = permute( permute( permute(
               i.z + vec4(0.0, i1.z, i2.z, 1.0 ))
             + i.y + vec4(0.0, i1.y, i2.y, 1.0 ))
             + i.x + vec4(0.0, i1.x, i2.x, 1.0 ));

      // Gradients
      // ( N*N points uniformly over a square, mapped onto an octahedron.)
      float n_ = 1.0/7.0; // N=7
      vec3  ns = n_ * D.wyz - D.xzx;

      vec4 j = p - 49.0 * floor(p * ns.z *ns.z);  //  mod(p,N*N)

      vec4 x_ = floor(j * ns.z);
      vec4 y_ = floor(j - 7.0 * x_ );    // mod(j,N)

      vec4 x = x_ *ns.x + ns.yyyy;
      vec4 y = y_ *ns.x + ns.yyyy;
      vec4 h = 1.0 - abs(x) - abs(y);

      vec4 b0 = vec4( x.xy, y.xy );
      vec4 b1 = vec4( x.zw, y.zw );

      //vec4 s0 = vec4(lessThan(b0,0.0))*2.0 - 1.0;
      //vec4 s1 = vec4(lessThan(b1,0.0))*2.0 - 1.0;
      vec4 s0 = floor(b0)*2.0 + 1.0;
      vec4 s1 = floor(b1)*2.0 + 1.0;
      vec4 sh = -step(h, vec4(0.0));

      vec4 a0 = b0.xzyw + s0.xzyw*sh.xxyy ;
      vec4 a1 = b1.xzyw + s1.xzyw*sh.zzww ;

      vec3 p0 = vec3(a0.xy,h.x);
      vec3 p1 = vec3(a0.zw,h.y);
      vec3 p2 = vec3(a1.xy,h.z);
      vec3 p3 = vec3(a1.zw,h.w);

      //Normalise gradients
      vec4 norm = taylorInvSqrt(vec4(dot(p0,p0), dot(p1,p1), dot(p2, p2), dot(p3,p3)));
      p0 *= norm.x;
      p1 *= norm.y;
      p2 *= norm.z;
      p3 *= norm.w;

      // Mix final noise value
      vec4 m = max(0.6 - vec4(dot(x0,x0), dot(x1,x1), dot(x2,x2), dot(x3,x3)), 0.0);
      m = m * m;
      return 42.0 * dot( m*m, vec4( dot(p0,x0), dot(p1,x1),
                                    dot(p2,x2), dot(p3,x3) ) );
  }

  float height( const in vec3 pos )
  {
      // Perturb the y position by a wave function in (x, t)
      const float twoPi = 2.0 * 3.14159;
      float k = twoPi / lambda;
      float omega = twoPi / period;

      float y = amplitude * sin( k * pos.x - omega * time );

      // Further perturb by a noise function
      y += snoise( 0.27 * vec3( 0.4 * pos.x, 3.0, 2.0 * pos.z - 0.5 * time ) );

      return y;
  }

  void main()
  {
      // Calculate y value based upon input coordinates and time
      vec3 pos = vertexPosition;
      pos.y = height( pos );

      // Estimate normal vector by calculating the y value at small offsets
      // and then taking the cross product of the differences
      float offset = 0.5;
      vec3 posOffsetX = vertexPosition + vec3( offset, 0.0, 0.0 );
      posOffsetX.y = height( posOffsetX );
      vec3 posOffsetZ = vertexPosition + vec3( 0.0, 0.0, offset );
      posOffsetZ.y = height( posOffsetZ );

      vec3 dydx = posOffsetX - pos;
      vec3 dydz = posOffsetZ - pos;
      vec3 normal = cross( dydz, dydx );

      // Transform the position and normal to eye space for lighting
      vs_out.normal = normalize( modelViewNormal * normal );
      vs_out.position = vec3( modelView * vec4( pos, 1.0 ) );

      gl_Position = mvp * vec4( pos, 1.0 );
  }