# 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)
//

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 ));

// ( 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);

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 * 3.14159265358979323846;
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 );
}```