[ReactNative] PixelRatio docs

Martin Konicek · Martin Konicek · commit b7253dc6045c · 2015-07-27T09:40:08.000-08:00
Summary: Update docs for `PixelRatio` in preparation for open sourcing React Native for Android. See http://stackoverflow.com/questions/11581649/about-android-image-and-asset-sizes
diff --git a/Libraries/Utilities/PixelRatio.js b/Libraries/Utilities/PixelRatio.js
@@ -20,9 +20,11 @@ var Dimensions = require('Dimensions');
  *
  * ### Displaying a line that's as thin as the device permits
  *
- * A width of 1 is actually pretty thick on an iPhone 4+, we can do one that's
- * thinner using a width of `1 / PixelRatio.get()`. It's a technique that works
- * on all the devices independent of their pixel density.
+ * A width of 1 is actually pretty thick on devices with high pixel density
+ * (such as iPhone 4+ and many Android devices), we can make one that's
+ * thinner using a width of `1 / PixelRatio.get()`.
+ * It's a technique that works on all the devices independent of their
+ * pixel density.
  *
  * ```
  * style={{ borderWidth: 1 / PixelRatio.get() }}
@@ -46,12 +48,18 @@ class PixelRatio {
   /**
    * Returns the device pixel density. Some examples:
    *
+   *   - PixelRatio.get() === 1
+   *     - mdpi Android devices (160 dpi)
+   *   - PixelRatio.get() === 1.5
+   *     - hdpi Android devices (240 dpi)
    *   - PixelRatio.get() === 2
    *     - iPhone 4, 4S
    *     - iPhone 5, 5c, 5s
    *     - iPhone 6
+   *     - xhdpi Android devices (320 dpi)
    *   - PixelRatio.get() === 3
    *     - iPhone 6 plus
+   *     - xxhdpi Android devices (480 dpi)
    *   - PixelRatio.get() === 3.5
    *     - Nexus 6
    */
@@ -68,6 +76,7 @@ class PixelRatio {
    *
    * Currently this is only implemented on Android and reflects the user preference set in
    * Settings > Display > Font size, on iOS it will always return the default pixel ratio.
+   * @platform android
    */
   static getFontScale(): number {
     return Dimensions.get('window').fontScale || PixelRatio.get();
