THREE.WebGLProgram: shader error:  0 35715 false gl.getProgramInfoLog Varyings over maximum register limit

function WebGLProgram( renderer, cacheKey, parameters, bindingStates ) {
    const gl = renderer.getContext();
    // ...
    const program = gl.createProgram(); // 創(chuàng)建一個program
    // ...
    // 動態(tài)生成頂點(diǎn)著色器和片元著色器的源代碼
    const glVertexShader = WebGLShader( gl, gl.VERTEX_SHADER, vertexGlsl ); // 創(chuàng)建并編譯頂點(diǎn)著色器
    const glFragmentShader = WebGLShader( gl, gl.FRAGMENT_SHADER, fragmentGlsl ); // 創(chuàng)建并編譯片元著色器
    gl.attachShader( program, glVertexShader ); // 和program綁定
    gl.attachShader( program, glFragmentShader ); // 和program綁定
    // ...
    gl.linkProgram( program );
    // ... 檢查上述過程是否報錯
    const programLog = gl.getProgramInfoLog( program ).trim(); // 獲取報錯信息
    if (...) { // 出錯判斷
        console.error(... 'gl.getProgramInfoLog' ...) // 報錯位置
    }
}

function WebGLShader( gl, type, string ) {
    const shader = gl.createShader( type );
    gl.shaderSource( shader, string );
    gl.compileShader( shader );
    return shader;
}

let vertexShader = parameters.vertexShader;
// ...
if ( parameters.isRawShaderMaterial ) { // 自定義著色器，不考慮
} else { // THREE.js提供的著色器
    prefixVertex = [...]
}
const vertexGlsl = prefixVertex + vertexShader;

parameters.shadowMapEnabled ? '#define USE_SHADOWMAP' : '',
parameters.shadowMapEnabled ? '#define ' + shadowMapTypeDefine : '',

function acquireProgram( parameters, cacheKey ) {
    // ...
    program = new WebGLProgram( renderer, cacheKey, parameters, bindingStates );
    // ...
}

function initMaterial( material, scene, object ) {
    // ...
    const shadowsArray = currentRenderState.state.shadowsArray;
    // ...
    const parameters = programCache.getParameters( material, lights.state, shadowsArray, ... );
    // ...
    program = programCache.acquireProgram( parameters, programCacheKey );
    // ...
}

programCache = new WebGLPrograms( _this, extensions, capabilities, bindingStates );

function getParameters( material, lights, shadows, scene, nClipPlanes, nClipIntersection, object ) {
    // ...
    shadowMapEnabled: renderer.shadowMap.enabled && shadows.length > 0
    // ...
}

const shadowsArray = currentRenderState.state.shadowsArray;

currentRenderState = renderStates.get( scene, _currentArrayCamera || camera ); // 找了一處賦值

renderStates = new WebGLRenderStates()

renderState = new WebGLRenderState();
renderStates.set( scene, new WeakMap() );
renderStates.get( scene ).set( camera, renderState );

function pushShadow( shadowLight ) {
    shadowsArray.push( shadowLight );
}

this.compile = function ( scene, camera ) {
    // 前面講過renderStates是一個雙層的WeakMap，先根據(jù)scene獲取一次，再根據(jù)camera獲取一次
    currentRenderState = renderStates.get( scene, camera );
    currentRenderState.init();
    // 收集光源信息
    scene.traverse( function ( object ) {
        if ( object.isLight ) { // 是光源
            currentRenderState.pushLight( object );
            if ( object.castShadow ) { // 光源設(shè)置了投影
                currentRenderState.pushShadow( object );
            }
        }
    } );
    currentRenderState.setupLights( camera );
    const compiled = new WeakMap();
    scene.traverse( function ( object ) {
        // ... initMaterial
    } );
};

parameters.shadowMapEnabled ? '#define USE_SHADOWMAP' : '',

function WebGLProgram( renderer, cacheKey, parameters, bindingStates ) {
    let vertexShader = parameters.vertexShader;
}

function getParameters( material, lights, shadows, scene, nClipPlanes, nClipIntersection, object ) {
    // ...
    const shaderID = shaderIDs[ material.type ];
    // ...
    let vertexShader, fragmentShader;
    if ( shaderID ) { // 內(nèi)置頂點(diǎn)著色器/片元著色器代碼
        const shader = ShaderLib[ shaderID ];
        vertexShader = shader.vertexShader;
        fragmentShader = shader.fragmentShader;
    }
    // ...
}

const shaderIDs = {
    MeshDepthMaterial: 'depth',
    MeshDistanceMaterial: 'distanceRGBA',
    MeshNormalMaterial: 'normal',
    MeshBasicMaterial: 'basic',
    MeshLambertMaterial: 'lambert',
    MeshPhongMaterial: 'phong',
    MeshToonMaterial: 'toon',
    MeshStandardMaterial: 'physical',
    MeshPhysicalMaterial: 'physical',
    MeshMatcapMaterial: 'matcap',
    LineBasicMaterial: 'basic',
    LineDashedMaterial: 'dashed',
    PointsMaterial: 'points',
    ShadowMaterial: 'shadow',
    SpriteMaterial: 'sprite'
};

ShaderLib.physical = {
    // ...
    vertexShader: ShaderChunk.meshphysical_vert,
    // ...
}

import meshphysical_vert from './ShaderLib/meshphysical_vert.glsl.js';
export const ShaderChunk = {
    // ...
    meshphysical_vert: meshphysical_vert,
    // ...
}

#include <shadowmap_pars_vertex>

export default /* glsl */`
#ifdef USE_SHADOWMAP
    #if NUM_DIR_LIGHT_SHADOWS > 0
        uniform mat4 directionalShadowMatrix[ NUM_DIR_LIGHT_SHADOWS ];
        varying vec4 vDirectionalShadowCoord[ NUM_DIR_LIGHT_SHADOWS ];
        # ...
    #endif
    #if NUM_SPOT_LIGHT_SHADOWS > 0
        uniform mat4 spotShadowMatrix[ NUM_SPOT_LIGHT_SHADOWS ];
        varying vec4 vSpotShadowCoord[ NUM_SPOT_LIGHT_SHADOWS ];
        # ...
    #endif
    #if NUM_POINT_LIGHT_SHADOWS > 0
        uniform mat4 pointShadowMatrix[ NUM_POINT_LIGHT_SHADOWS ];
        varying vec4 vPointShadowCoord[ NUM_POINT_LIGHT_SHADOWS ];
        # ...
    #endif
#endif
`;

#define USE_SHADOWMAP

varying vec4 vSpotShadowCoord[ NUM_SPOT_LIGHT_SHADOWS ];

function replaceLightNums( string, parameters ) {
    return string
        // ...
        .replace( /NUM_SPOT_LIGHT_SHADOWS/g, parameters.numSpotLightShadows )
        // ...
}

vertexShader = replaceLightNums( vertexShader, parameters );

function getParameters( material, lights, shadows, scene, nClipPlanes, nClipIntersection, object ) {
    // ...
    numSpotLightShadows: lights.spotShadowMap.length,
    // ...
}

function setup( lights, shadows, camera ) {
    // ...
    let numSpotShadows = 0;
    // ...
    for ( let i = 0, l = lights.length; i < l; i ++ ) {
        // ...
        if ( light.castShadow ) {
            // ...
            numSpotShadows ++;
            // ...
        }
        // ...
    }
    // ...
    state.spotShadowMap.length = numSpotShadows;
    // ...
}