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Libraries/Utilities/PixelRatio.js

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+/**
+ * Copyright 2004-present Facebook. All Rights Reserved.
+ *
+ * @providesModule PixelRatio
+ */
+'use strict';
+
+var Dimensions = require('Dimensions');
+
+/**
+ * PixelRatio class gives access to the device pixel density.
+ *
+ * Some examples:
+ *   - PixelRatio.get() === 2
+ *     - iPhone 4, 4S
+ *     - iPhone 5, 5c, 5s
+ *     - iPhone 6
+ *
+ *   - PixelRatio.get() === 3
+ *     - iPhone 6 plus
+ *
+ * There are a few use cases for using PixelRatio:
+ *
+ * == 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.
+ *
+ *   style={{ borderWidth: 1 / PixelRatio.get() }}
+ *
+ * == Fetching a correctly sized image
+ *
+ * You should get a higher resolution image if you are on a high pixel density
+ * device. A good rule of thumb is to multiply the size of the image you display
+ * by the pixel ratio.
+ *
+ *   var image = getImage({
+ *     width: 200 * PixelRatio.get(),
+ *     height: 100 * PixelRatio.get()
+ *   });
+ *   <Image source={image} style={{width: 200, height: 100}} />
+ */
+class PixelRatio {
+  static get() {
+    return Dimensions.get('window').scale;
+  }
+
+  static startDetecting() {
+    // no-op for iOS, but this is useful for other platforms
+  }
+};
+
+module.exports = PixelRatio;