devicePixelRatio property

The number of device pixels for each logical pixel for the screen this view is displayed on.

This number might not be a power of two. Indeed, it might not even be an integer. For example, the Nexus 6 has a device pixel ratio of 3.5.

Device pixels are also referred to as physical pixels. Logical pixels are also referred to as device-independent or resolution-independent pixels.

By definition, there are roughly 38 logical pixels per centimeter, or about 96 logical pixels per inch, of the physical display. The value returned by devicePixelRatio is ultimately obtained either from the hardware itself, the device drivers, or a hard-coded value stored in the operating system or firmware, and may be inaccurate, sometimes by a significant margin.

The Flutter framework operates in logical pixels, so it is rarely necessary to directly deal with this property.

When this changes, PlatformDispatcher.onMetricsChanged is called. When using the Flutter framework, using MediaQuery.of to obtain the device pixel ratio (via MediaQueryData.devicePixelRatio), instead of directly obtaining the devicePixelRatio from a FlutterView, will automatically cause any widgets dependent on this value to rebuild when it changes, without having to listen to PlatformDispatcher.onMetricsChanged.

See also:

• WidgetsBindingObserver, for a mechanism at the widgets layer to observe when this value changes.
• Display.devicePixelRatio, which reports the DPR of the display. The value here is equal to the value exposed on display.