text: /**
   * @author alteredq / http://alteredqualia.com/
   *
   */
  import {Color,
          ShaderChunk,
          UniformsLib,
          UniformsUtils,
          Vector2 } from 'three'
  
  /* -------------------------------------------------------------------------
  //  Dynamic terrain shader
  //    - Blinn-Phong
  //    - height + normal + diffuse1 + diffuse2 + specular + detail maps
  //    - point, directional and hemisphere lights (use with "lights: true" material option)
  //    - shadow maps receiving
   ------------------------------------------------------------------------- */
  
  let ShaderTerrain = {
  
    uniforms: UniformsUtils.merge( [
  
      UniformsLib[ "fog" ],
      UniformsLib[ "lights" ],
  
      {
  
        "enableDiffuse1": { value: 0 },
        "enableDiffuse2": { value: 0 },
        "enableSpecular": { value: 0 },
        "enableReflection": { value: 0 },
  
        "tDiffuse1": { value: null },
        "tDiffuse2": { value: null },
        "tDetail": { value: null },
        "tNormal": { value: null },
        "tSpecular": { value: null },
        "tDisplacement": { value: null },
  
        "uNormalScale": { value: 1.0 },
  
        "uDisplacementBias": { value: 0.0 },
        "uDisplacementScale": { value: 1.0 },
  
        "diffuse": { value: new Color( 0xeeeeee ) },
        "specular": { value: new Color( 0x111111 ) },
        "shininess": { value: 30 },
        "opacity": { value: 1 },
  
        "uRepeatBase": { value: new Vector2( 1, 1 ) },
        "uRepeatOverlay": { value: new Vector2( 1, 1 ) },
  
        "uOffset": { value: new Vector2( 0, 0 ) }
  
      }
  
    ] ),
  
    fragmentShader: [
  
      "uniform vec3 diffuse;",
      "uniform vec3 specular;",
      "uniform float shininess;",
      "uniform float opacity;",
  
      "uniform bool enableDiffuse1;",
      "uniform bool enableDiffuse2;",
      "uniform bool enableSpecular;",
  
      "uniform sampler2D tDiffuse1;",
      "uniform sampler2D tDiffuse2;",
      "uniform sampler2D tDetail;",
      "uniform sampler2D tNormal;",
      "uniform sampler2D tSpecular;",
      "uniform sampler2D tDisplacement;",
  
      "uniform float uNormalScale;",
  
      "uniform vec2 uRepeatOverlay;",
      "uniform vec2 uRepeatBase;",
  
      "uniform vec2 uOffset;",
  
      "varying vec3 vTangent;",
      "varying vec3 vBinormal;",
      "varying vec3 vNormal;",
      "varying vec2 vUv;",
  
      "varying vec3 vViewPosition;",
  
      ShaderChunk[ "common" ],
      ShaderChunk[ "bsdfs" ],
      ShaderChunk[ "lights_pars" ],
      ShaderChunk[ "shadowmap_pars_fragment" ],
      ShaderChunk[ "fog_pars_fragment" ],
  
      "float calcLightAttenuation( float lightDistance, float cutoffDistance, float decayExponent ) {",
        "if ( decayExponent > 0.0 ) {",
          "return pow( saturate( - lightDistance / cutoffDistance + 1.0 ), decayExponent );",
        "}",
        "return 1.0;",
      "}",
  
      "void main() {",
  
        "vec3 outgoingLight = vec3( 0.0 );",  // outgoing light does not have an alpha, the surface does
        "vec4 diffuseColor = vec4( diffuse, opacity );",
  
        "vec3 specularTex = vec3( 1.0 );",
  
        "vec2 uvOverlay = uRepeatOverlay * vUv + uOffset;",
        "vec2 uvBase = uRepeatBase * vUv;",
  
        "vec3 normalTex = texture2D( tDetail, uvOverlay ).xyz * 2.0 - 1.0;",
        "normalTex.xy *= uNormalScale;",
        "normalTex = normalize( normalTex );",
  
        "if( enableDiffuse1 && enableDiffuse2 ) {",
  
          "vec4 colDiffuse1 = texture2D( tDiffuse1, uvOverlay );",
          "vec4 colDiffuse2 = texture2D( tDiffuse2, uvOverlay );",
  
          "colDiffuse1 = GammaToLinear( colDiffuse1, float( GAMMA_FACTOR ) );",
          "colDiffuse2 = GammaToLinear( colDiffuse2, float( GAMMA_FACTOR ) );",
  
          "diffuseColor *= mix ( colDiffuse1, colDiffuse2, 1.0 - texture2D( tDisplacement, uvBase ) );",
  
        " } else if( enableDiffuse1 ) {",
  
          "diffuseColor *= texture2D( tDiffuse1, uvOverlay );",
  
        "} else if( enableDiffuse2 ) {",
  
          "diffuseColor *= texture2D( tDiffuse2, uvOverlay );",
  
        "}",
  
        "if( enableSpecular )",
          "specularTex = texture2D( tSpecular, uvOverlay ).xyz;",
  
        "mat3 tsb = mat3( vTangent, vBinormal, vNormal );",
        "vec3 finalNormal = tsb * normalTex;",
  
        "vec3 normal = normalize( finalNormal );",
        "vec3 viewPosition = normalize( vViewPosition );",
  
        "vec3 totalDiffuseLight = vec3( 0.0 );",
        "vec3 totalSpecularLight = vec3( 0.0 );",
  
        // point lights
  
        "#if NUM_POINT_LIGHTS > 0",
  
          "for ( int i = 0; i < NUM_POINT_LIGHTS; i ++ ) {",
  
            "vec3 lVector = pointLights[ i ].position + vViewPosition.xyz;",
  
            "float attenuation = calcLightAttenuation( length( lVector ), pointLights[ i ].distance, pointLights[ i ].decay );",
  
            "lVector = normalize( lVector );",
  
            "vec3 pointHalfVector = normalize( lVector + viewPosition );",
  
            "float pointDotNormalHalf = max( dot( normal, pointHalfVector ), 0.0 );",
            "float pointDiffuseWeight = max( dot( normal, lVector ), 0.0 );",
  
            "float pointSpecularWeight = specularTex.r * max( pow( pointDotNormalHalf, shininess ), 0.0 );",
  
            "totalDiffuseLight += attenuation * pointLights[ i ].color * pointDiffuseWeight;",
            "totalSpecularLight += attenuation * pointLights[ i ].color * specular * pointSpecularWeight * pointDiffuseWeight;",
  
          "}",
  
        "#endif",
  
        // directional lights
  
        "#if NUM_DIR_LIGHTS > 0",
  
          "vec3 dirDiffuse = vec3( 0.0 );",
          "vec3 dirSpecular = vec3( 0.0 );",
  
          "for( int i = 0; i < NUM_DIR_LIGHTS; i++ ) {",
  
            "vec3 dirVector = directionalLights[ i ].direction;",
            "vec3 dirHalfVector = normalize( dirVector + viewPosition );",
  
            "float dirDotNormalHalf = max( dot( normal, dirHalfVector ), 0.0 );",
            "float dirDiffuseWeight = max( dot( normal, dirVector ), 0.0 );",
  
            "float dirSpecularWeight = specularTex.r * max( pow( dirDotNormalHalf, shininess ), 0.0 );",
  
            "totalDiffuseLight += directionalLights[ i ].color * dirDiffuseWeight;",
            "totalSpecularLight += directionalLights[ i ].color * specular * dirSpecularWeight * dirDiffuseWeight;",
  
          "}",
  
        "#endif",
  
        // hemisphere lights
  
        "#if NUM_HEMI_LIGHTS > 0",
  
          "vec3 hemiDiffuse  = vec3( 0.0 );",
          "vec3 hemiSpecular = vec3( 0.0 );",
  
          "for( int i = 0; i < NUM_HEMI_LIGHTS; i ++ ) {",
  
            "vec3 lVector = hemisphereLightDirection[ i ];",
  
            // diffuse
  
            "float dotProduct = dot( normal, lVector );",
            "float hemiDiffuseWeight = 0.5 * dotProduct + 0.5;",
  
            "totalDiffuseLight += mix( hemisphereLights[ i ].groundColor, hemisphereLights[ i ].skyColor, hemiDiffuseWeight );",
  
            // specular (sky light)
  
            "float hemiSpecularWeight = 0.0;",
  
            "vec3 hemiHalfVectorSky = normalize( lVector + viewPosition );",
            "float hemiDotNormalHalfSky = 0.5 * dot( normal, hemiHalfVectorSky ) + 0.5;",
            "hemiSpecularWeight += specularTex.r * max( pow( hemiDotNormalHalfSky, shininess ), 0.0 );",
  
            // specular (ground light)
  
            "vec3 lVectorGround = -lVector;",
  
            "vec3 hemiHalfVectorGround = normalize( lVectorGround + viewPosition );",
            "float hemiDotNormalHalfGround = 0.5 * dot( normal, hemiHalfVectorGround ) + 0.5;",
            "hemiSpecularWeight += specularTex.r * max( pow( hemiDotNormalHalfGround, shininess ), 0.0 );",
  
            "totalSpecularLight += specular * mix( hemisphereLights[ i ].groundColor, hemisphereLights[ i ].skyColor, hemiDiffuseWeight ) * hemiSpecularWeight * hemiDiffuseWeight;",
  
          "}",
  
        "#endif",
  
        "outgoingLight += diffuseColor.xyz * ( totalDiffuseLight + ambientLightColor + totalSpecularLight );",
        // "outgoingLight += diffuseColor.xyz;",
  
        "gl_FragColor = vec4( outgoingLight, diffuseColor.a );",  // TODO, this should be pre-multiplied to allow for bright highlights on very transparent objects
  
        ShaderChunk[ "fog_fragment" ],
  
      "}"
  
    ].join( "\n" ),
  
    vertexShader: [
  
      "attribute vec4 tangent;",
  
      "uniform vec2 uRepeatBase;",
  
      "uniform sampler2D tNormal;",
  
      "#ifdef VERTEX_TEXTURES",
  
        "uniform sampler2D tDisplacement;",
        "uniform float uDisplacementScale;",
        "uniform float uDisplacementBias;",
  
      "#endif",
  
      "varying vec3 vTangent;",
      "varying vec3 vBinormal;",
      "varying vec3 vNormal;",
      "varying vec2 vUv;",
  
      "varying vec3 vViewPosition;",
  
      ShaderChunk[ "shadowmap_pars_vertex" ],
      ShaderChunk[ "fog_pars_vertex" ],
  
      "void main() {",
  
        "vNormal = normalize( normalMatrix * normal );",
  
        // tangent and binormal vectors
  
        "vTangent = normalize( normalMatrix * tangent.xyz );",
  
        "vBinormal = cross( vNormal, vTangent ) * tangent.w;",
        "vBinormal = normalize( vBinormal );",
  
        // texture coordinates
  
        "vUv = uv;",
  
        "vec2 uvBase = uv * uRepeatBase;",
  
        // displacement mapping
  
        "#ifdef VERTEX_TEXTURES",
  
          "vec3 dv = texture2D( tDisplacement, uvBase ).xyz;",
          "float df = uDisplacementScale * dv.x + uDisplacementBias;",
          "vec3 displacedPosition = normal * df + position;",
  
          "vec4 worldPosition = modelMatrix * vec4( displacedPosition, 1.0 );",
          "vec4 mvPosition = modelViewMatrix * vec4( displacedPosition, 1.0 );",
  
        "#else",
  
          "vec4 worldPosition = modelMatrix * vec4( position, 1.0 );",
          "vec4 mvPosition = modelViewMatrix * vec4( position, 1.0 );",
  
        "#endif",
  
        // "gl_Position = projectionMatrix * mvPosition;",
        "gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );",
  
        "vViewPosition = -mvPosition.xyz;",
  
        "vec3 normalTex = texture2D( tNormal, uvBase ).xyz * 2.0 - 1.0;",
        "vNormal = normalMatrix * normalTex;",
  
        ShaderChunk[ "shadowmap_vertex" ],
        ShaderChunk[ "fog_vertex" ],
  
      "}"
  
    ].join( "\n" )
  
  
  }
  
  
  
  
  export default ShaderTerrain
  
  
  
  
  