Cesium源码之Label(二)

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 };