我们查看Cesium源码时，有时会发现源码中有大量的includeStart开头的注释，如下图所示。
这里面大多是调试信息，当使用gulp打包时，removePragmas参数设置为true，则会删除includeStart和includeEnd之间的js语句。
源码：
1 /**
2 * A Label draws viewport-aligned text positioned in the 3D scene. This constructor
3 * should not be used directly, instead create labels by calling {@link LabelCollection#add}.
4 *
5 * @alias Label
6 * @internalConstructor
7 * @class
8 *
9 * @exception {DeveloperError} translucencyByDistance.far must be greater than translucencyByDistance.near
10 * @exception {DeveloperError} pixelOffsetScaleByDistance.far must be greater than pixelOffsetScaleByDistance.near
11 * @exception {DeveloperError} distanceDisplayCondition.far must be greater than distanceDisplayCondition.near
12 *
13 * @see LabelCollection
14 * @see LabelCollection#add
15 *
16 * @demo {@link https://sandcastle.cesium.com/index.html?src=Labels.html|Cesium Sandcastle Labels Demo}
17 */
18 function Label(options, labelCollection) {
19 options = defaultValue(options, defaultValue.EMPTY_OBJECT);
20
21
22 //>>includeStart('debug', pragmas.debug);
23 //距离摄像机的位置不能小于0
24 // 设置为零时，始终应用深度测试
25 if (
26 defined(options.disableDepthTestDistance) &&
27 options.disableDepthTestDistance < 0.0
28 ) {
29 throw new DeveloperError(
30 "disableDepthTestDistance must be greater than 0.0."
31 );
32 }
33 //>>includeEnd('debug');
34
35 //根据距离变透明的属性
36 var translucencyByDistance = options.translucencyByDistance;
37
38 //根据距离的像素偏移
39 var pixelOffsetScaleByDistance = options.pixelOffsetScaleByDistance;
40
41 //根据距离的大小变化
42 var scaleByDistance = options.scaleByDistance;
43
44 //根据距离的label display
45 var distanceDisplayCondition = options.distanceDisplayCondition;
46
47
48 //从这里开始是判断上述那些属性存不存在、合不合理
49
50 if (defined(translucencyByDistance)) {
51 //>>includeStart('debug', pragmas.debug);
52 //远需大于近
53 if (translucencyByDistance.far <= translucencyByDistance.near) {
54 throw new DeveloperError(
55 "translucencyByDistance.far must be greater than translucencyByDistance.near."
56 );
57 }
58 //>>includeEnd('debug');
59 translucencyByDistance = NearFarScalar.clone(translucencyByDistance);
60 }
61 if (defined(pixelOffsetScaleByDistance)) {
62 //>>includeStart('debug', pragmas.debug);
63 if (pixelOffsetScaleByDistance.far <= pixelOffsetScaleByDistance.near) {
64 throw new DeveloperError(
65 "pixelOffsetScaleByDistance.far must be greater than pixelOffsetScaleByDistance.near."
66 );
67 }
68 //>>includeEnd('debug');
69 pixelOffsetScaleByDistance = NearFarScalar.clone(
70 pixelOffsetScaleByDistance
71 );
72 }
73 if (defined(scaleByDistance)) {
74 //>>includeStart('debug', pragmas.debug);
75 if (scaleByDistance.far <= scaleByDistance.near) {
76 throw new DeveloperError(
77 "scaleByDistance.far must be greater than scaleByDistance.near."
78 );
79 }
80 //>>includeEnd('debug');
81 scaleByDistance = NearFarScalar.clone(scaleByDistance);
82 }
83 if (defined(distanceDisplayCondition)) {
84 //>>includeStart('debug', pragmas.debug);
85 if (distanceDisplayCondition.far <= distanceDisplayCondition.near) {
86 throw new DeveloperError(
87 "distanceDisplayCondition.far must be greater than distanceDisplayCondition.near."
88 );
89 }
90 //>>includeEnd('debug');
91 distanceDisplayCondition = DistanceDisplayCondition.clone(
92 distanceDisplayCondition
93 );
94 }
95 //判断上述那些属性存不存在、合不合理到这里结束
96
97 //将options拷贝一份作为自己的私有属性
98 this._renderedText = undefined;
99 this._text = undefined;
100 this._show = defaultValue(options.show, true);
101 this._font = defaultValue(options.font, "30px sans-serif");
102 this._fillColor = Color.clone(defaultValue(options.fillColor, Color.WHITE));
103 this._outlineColor = Color.clone(
104 defaultValue(options.outlineColor, Color.BLACK)
105 );
106 this._outlineWidth = defaultValue(options.outlineWidth, 1.0);
107 this._showBackground = defaultValue(options.showBackground, false);
108 this._backgroundColor = defaultValue(
109 options.backgroundColor,
110 new Color(0.165, 0.165, 0.165, 0.8)
111 );
112 this._backgroundPadding = defaultValue(
113 options.backgroundPadding,
114 new Cartesian2(7, 5)
115 );
116 this._style = defaultValue(options.style, LabelStyle.FILL);
117 this._verticalOrigin = defaultValue(
118 options.verticalOrigin,
119 VerticalOrigin.BASELINE
120 );
121 this._horizontalOrigin = defaultValue(
122 options.horizontalOrigin,
123 HorizontalOrigin.LEFT
124 );
125 this._pixelOffset = Cartesian2.clone(
126 defaultValue(options.pixelOffset, Cartesian2.ZERO)
127 );
128 this._eyeOffset = Cartesian3.clone(
129 defaultValue(options.eyeOffset, Cartesian3.ZERO)
130 );
131 this._position = Cartesian3.clone(
132 defaultValue(options.position, Cartesian3.ZERO)
133 );
134 this._scale = defaultValue(options.scale, 1.0);
135 this._id = options.id;
136 this._translucencyByDistance = translucencyByDistance;
137 this._pixelOffsetScaleByDistance = pixelOffsetScaleByDistance;
138 this._scaleByDistance = scaleByDistance;
139 this._heightReference = defaultValue(
140 options.heightReference,
141 HeightReference.NONE
142 );
143 this._distanceDisplayCondition = distanceDisplayCondition;
144 this._disableDepthTestDistance = options.disableDepthTestDistance;
145
146 this._labelCollection = labelCollection;
147 this._glyphs = [];
148 this._backgroundBillboard = undefined;
149 this._batchIndex = undefined; // Used only by Vector3DTilePoints and BillboardCollection
150
151 this._rebindAllGlyphs = true;
152 this._repositionAllGlyphs = true;
153
154 this._actualClampedPosition = undefined;
155 this._removeCallbackFunc = undefined;
156 this._mode = undefined;
157
158 this._clusterShow = true;
159
160 this.text = defaultValue(options.text, "");
161
162 this._relativeSize = 1.0;
163
164 parseFont(this);
165
166 this._updateClamping();
167 }
前面就是简单的对options进行判断之类的，最重要的就是最后一行的_updateClamping()方法
1 Label.prototype._updateClamping = function () {
2 Billboard._updateClamping(this._labelCollection, this);
3 };
继续点，这个函数对传入的label进行位置变换
1 Billboard._updateClamping = function (collection, owner) {
2 var scene = collection._scene;
3 if (!defined(scene) || !defined(scene.globe)) {
4 //>>includeStart('debug', pragmas.debug);
5 if (owner._heightReference !== HeightReference.NONE) {
6 throw new DeveloperError(
7 "Height reference is not supported without a scene and globe."
8 );
9 }
10 //>>includeEnd('debug');
11 return;
12 }
13
14 var globe = scene.globe;
15 var ellipsoid = globe.ellipsoid;
16 var surface = globe._surface;
17
18 var mode = scene.frameState.mode;
19
20 var modeChanged = mode !== owner._mode;
21 owner._mode = mode;
22
23 if (
24 (owner._heightReference === HeightReference.NONE || modeChanged) &&
25 defined(owner._removeCallbackFunc)
26 ) {
27 owner._removeCallbackFunc();
28 owner._removeCallbackFunc = undefined;
29 owner._clampedPosition = undefined;
30 }
31
32 if (
33 owner._heightReference === HeightReference.NONE ||
34 !defined(owner._position)
35 ) {
36 return;
37 }
38
39 var position = ellipsoid.cartesianToCartographic(owner._position);
40 if (!defined(position)) {
41 owner._actualClampedPosition = undefined;
42 return;
43 }
44
45 if (defined(owner._removeCallbackFunc)) {
46 owner._removeCallbackFunc();
47 }
48
49 function updateFunction(clampedPosition) {
50 if (owner._heightReference === HeightReference.RELATIVE_TO_GROUND) {
51 if (owner._mode === SceneMode.SCENE3D) {
52 var clampedCart = ellipsoid.cartesianToCartographic(
53 clampedPosition,
54 scratchCartographic
55 );
56 clampedCart.height += position.height;
57 ellipsoid.cartographicToCartesian(clampedCart, clampedPosition);
58 } else {
59 clampedPosition.x += position.height;
60 }
61 }
62 owner._clampedPosition = Cartesian3.clone(
63 clampedPosition,
64 owner._clampedPosition
65 );
66 }
67 owner._removeCallbackFunc = surface.updateHeight(position, updateFunction);
68
69 Cartographic.clone(position, scratchCartographic);
70 var height = globe.getHeight(position);
71 if (defined(height)) {
72 scratchCartographic.height = height;
73 }
74
75 ellipsoid.cartographicToCartesian(scratchCartographic, scratchPosition);
76
77 updateFunction(scratchPosition);
78 };
标签：debug,defaultValue,var,Label,owner,源码,._,Cesium,options From： https://www.cnblogs.com/LJXXXX/p/17058616.html