Improve docs for define tag

src/ol/ol.js

@@ -3,6 +3,13 @@ goog.require('goog.userAgent');
 goog.provide('ol');
 
 
+/**
+ * Constants defined with the define tag cannot be changed in application
+ * code, but can be set at compile time.
+ * Some reduce the size of the build in advanced compile mode.
+ */
+
+
 /**
  * @define {boolean} Assume touch.  Default is `false`.
  */
@@ -72,21 +79,26 @@ ol.DRAG_BOX_HYSTERESIS_PIXELS = 8;
 
 
 /**
- * @define {boolean} Enable the Canvas renderer.  Default is `true`.
+ * @define {boolean} Enable the Canvas renderer.  Default is `true`. Setting
+ *     this to false at compile time in advanced mode removes all code
+ *     supporting the Canvas renderer from the build.
  */
 ol.ENABLE_CANVAS = true;
 
 
 /**
  * @define {boolean} Enable the DOM renderer (used as a fallback where Canvas is
- *     not available).  Default is `true`.
+ *     not available).  Default is `true`. Setting this to false at compile time
+ *     in advanced mode removes all code supporting the DOM renderer from the
+ *     build.
  */
 ol.ENABLE_DOM = true;
 
 
 /**
  * @define {boolean} Enable rendering of ol.layer.Image based layers.  Default
- *     is `true`.
+ *     is `true`. Setting this to false at compile time in advanced mode removes
+ *     all code supporting Image layers from the build.
  */
 ol.ENABLE_IMAGE = true;
 
@@ -108,20 +120,24 @@ ol.ENABLE_PROJ4JS = true;
 
 /**
  * @define {boolean} Enable rendering of ol.layer.Tile based layers.  Default is
- *     `true`.
+ *     `true`. Setting this to false at compile time in advanced mode removes
+ *     all code supporting Tile layers from the build.
  */
 ol.ENABLE_TILE = true;
 
 
 /**
  * @define {boolean} Enable rendering of ol.layer.Vector based layers.  Default
- *     is `true`.
+ *     is `true`. Setting this to false at compile time in advanced mode removes
+ *     all code supporting Vector layers from the build.
  */
 ol.ENABLE_VECTOR = true;
 
 
 /**
- * @define {boolean} Enable the WebGL renderer.  Default is `true`.
+ * @define {boolean} Enable the WebGL renderer.  Default is `true`. Setting
+ *     this to false at compile time in advanced mode removes all code
+ *     supporting the WebGL renderer from the build.
  */
 ol.ENABLE_WEBGL = true;
 

tasks/readme.md

@@ -82,6 +82,7 @@ To export the `ol` symbol to somewhere other than the global namespace, a `names
 }
 ```
 
+The `defines` section of `build.json` above lists common settings for the Closure library in production code. The OL3 library also defines constants that can be set in this section at compile time. These are all defined in the `ol.js` source file; see the comments in this file to see what effect setting these would have. Some of them can reduce the size of the build in advanced mode.
 
 ## `generate-exports.js`