Cesium加载gltf报错：RuntimeError: Unsupported glTF Extension: KHR

我在使用Cesium加载gltf报错：

RuntimeError: Unsupported glTF Extension: KHR_technique_webgl

这个gltf是很久之前的数据，使用osgb转Cesium 3D tiles工具转换的是没有这个问题的。

解决办法：
在初始化地球之前，加入下面的代码即可：

/* 解决加载gltf2.0报错的问题 */
var fixGltf = function (gltf) {
    if (!gltf.extensionsUsed || !gltf.extensionsRequired) {
        return;
    }
    var v = gltf.extensionsUsed.indexOf('KHR_technique_webgl');
    var t = gltf.extensionsRequired.indexOf('KHR_technique_webgl');
    if (v !== -1) {
        gltf.extensionsRequired.splice(t, 1, 'KHR_techniques_webgl');
        gltf.extensionsUsed.splice(v, 1, 'KHR_techniques_webgl');
        gltf.extensions = gltf.extensions || {};
        gltf.extensions['KHR_techniques_webgl'] = {};
        gltf.extensions['KHR_techniques_webgl'].programs = gltf.programs;
        gltf.extensions['KHR_techniques_webgl'].shaders = gltf.shaders;
        gltf.extensions['KHR_techniques_webgl'].techniques = gltf.techniques;
        var techniques = gltf.extensions['KHR_techniques_webgl'].techniques;

        gltf.materials.forEach(function (mat, index) {
            gltf.materials[index].extensions['KHR_technique_webgl'].values = gltf.materials[index].values;
            gltf.materials[index].extensions['KHR_techniques_webgl'] = gltf.materials[index].extensions['KHR_technique_webgl'];

            var vtxfMaterialExtension = gltf.materials[index].extensions['KHR_techniques_webgl'];

            for (var value in vtxfMaterialExtension.values) {
                var us = techniques[vtxfMaterialExtension.technique].uniforms;
                for (var key in us) {
                    if (us[key] === value) {
                        vtxfMaterialExtension.values[key] = vtxfMaterialExtension.values[value];
                        delete vtxfMaterialExtension.values[value];
                        break;
                    }
                }
            };
        });

        techniques.forEach(function (t) {
            for (var attribute in t.attributes) {
                var name = t.attributes[attribute];
                t.attributes[attribute] = t.parameters[name];
            };

            for (var uniform in t.uniforms) {
                var name = t.uniforms[uniform];
                t.uniforms[uniform] = t.parameters[name];
            };
        });
    }
}

Object.defineProperties(Cesium.Model.prototype, {
    _cachedGltf: {
        set: function (value) {
            this._vtxf_cachedGltf = value;
            if (this._vtxf_cachedGltf && this._vtxf_cachedGltf._gltf) {
                fixGltf(this._vtxf_cachedGltf._gltf);
            }
        },
        get: function () {
            return this._vtxf_cachedGltf;
        }
    }
});

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