text: /**
   * @author alteredq / http://alteredqualia.com/
   */
  import * as THREE from 'three';
  
  export const ShaderTerrain = {
  
    /* -------------------------------------------------------------------------
    //  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
     ------------------------------------------------------------------------- */
  
    'terrain' : {
      uniforms: THREE.UniformsUtils.merge( [
        THREE.UniformsLib[ "fog" ],
        THREE.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 THREE.Color( 0xeeeeee ) },
          "specular": { value: new THREE.Color( 0x111111 ) },
          "shininess": { value: 30 },
          "opacity": { value: 1 },
          "uRepeatBase": { value: new THREE.Vector2( 1, 1 ) },
          "uRepeatOverlay": { value: new THREE.Vector2( 1, 1 ) },
          "uOffset": { value: new THREE.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;",
  
        THREE.ShaderChunk[ "common" ],
        THREE.ShaderChunk[ "bsdfs" ],
        THREE.ShaderChunk[ "lights_pars_begin" ],
        THREE.ShaderChunk[ "shadowmap_pars_fragment" ],
        THREE.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 );",
  
          "gl_FragColor = vec4( outgoingLight, diffuseColor.a );",  // TODO, this should be pre-multiplied to allow for bright highlights on very transparent objects
  
          THREE.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;",
  
        THREE.ShaderChunk[ "shadowmap_pars_vertex" ],
        THREE.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;",
  
          "vViewPosition = -mvPosition.xyz;",
  
          "vec3 normalTex = texture2D( tNormal, uvBase ).xyz * 2.0 - 1.0;",
          "vNormal = normalMatrix * normalTex;",
  
          THREE.ShaderChunk[ "shadowmap_vertex" ],
          THREE.ShaderChunk[ "fog_vertex" ],
  
        "}"
  
      ].join( "\n" )
  
    }
  
  };
  