Document that offsets are returned in logical pixels (#33620)

packages/flutter_driver/lib/src/common/geometry.dart

@@ -27,8 +27,11 @@ enum OffsetType {
 
 EnumIndex<OffsetType> _offsetTypeIndex = EnumIndex<OffsetType>(OffsetType.values);
 
-/// A Flutter Driver command that return the [offsetType] from the RenderObject
+/// A Flutter Driver command that returns the [offsetType] from the RenderObject
 /// identified by [finder].
+///
+/// The requested offset is returned in logical pixels, which can be translated
+/// to device pixels via [Window.devicePixelRatio].
 class GetOffset extends CommandWithTarget {
   /// The `finder` looks for an element to get its rect.
   GetOffset(SerializableFinder finder,  this.offsetType, { Duration timeout }) : super(finder, timeout: timeout);
@@ -51,14 +54,23 @@ class GetOffset extends CommandWithTarget {
 }
 
 /// The result of the [GetRect] command.
+///
+/// The offset is provided in logical pixels, which can be translated
+/// to device pixels via [Window.devicePixelRatio].
 class GetOffsetResult extends Result {
   /// Creates a result with the offset defined by [dx] and [dy].
   const GetOffsetResult({ this.dx = 0.0, this.dy = 0.0});
 
-  /// The x component of the offset.
+  /// The x component of the offset in logical pixels.
+  ///
+  /// The value can be translated to device pixels via
+  /// [Window.devicePixelRatio].
   final double dx;
 
-  /// The y component of the offset.
+  /// The y component of the offset in logical pixels.
+  ///
+  /// The value can be translated to device pixels via
+  /// [Window.devicePixelRatio].
   final double dy;
 
   /// Deserializes the result from JSON.

packages/flutter_driver/lib/src/driver/driver.dart

@@ -483,26 +483,41 @@ class FlutterDriver {
   }
 
   /// Returns the point at the top left of the widget identified by `finder`.
+  ///
+  /// The offset is expressed in logical pixels and can be translated to
+  /// device pixels via [Window.devicePixelRatio].
   Future<DriverOffset> getTopLeft(SerializableFinder finder, { Duration timeout }) async {
     return _getOffset(finder, OffsetType.topLeft, timeout: timeout);
   }
 
   /// Returns the point at the top right of the widget identified by `finder`.
+  ///
+  /// The offset is expressed in logical pixels and can be translated to
+  /// device pixels via [Window.devicePixelRatio].
   Future<DriverOffset> getTopRight(SerializableFinder finder, { Duration timeout }) async {
     return _getOffset(finder, OffsetType.topRight, timeout: timeout);
   }
 
   /// Returns the point at the bottom left of the widget identified by `finder`.
+  ///
+  /// The offset is expressed in logical pixels and can be translated to
+  /// device pixels via [Window.devicePixelRatio].
   Future<DriverOffset> getBottomLeft(SerializableFinder finder, { Duration timeout }) async {
     return _getOffset(finder, OffsetType.bottomLeft, timeout: timeout);
   }
 
   /// Returns the point at the bottom right of the widget identified by `finder`.
+  ///
+  /// The offset is expressed in logical pixels and can be translated to
+  /// device pixels via [Window.devicePixelRatio].
   Future<DriverOffset> getBottomRight(SerializableFinder finder, { Duration timeout }) async {
     return _getOffset(finder, OffsetType.bottomRight, timeout: timeout);
   }
 
   /// Returns the point at the center of the widget identified by `finder`.
+  ///
+  /// The offset is expressed in logical pixels and can be translated to
+  /// device pixels via [Window.devicePixelRatio].
   Future<DriverOffset> getCenter(SerializableFinder finder, { Duration timeout }) async {
     return _getOffset(finder, OffsetType.center, timeout: timeout);
   }