ability to specify device pixel ratio manually

Runtime/engine/WidgetCanvas.cs

         }
 
         protected override double queryDevicePixelRatio() {
-            return this._widgetCanvas.pixelRatio;
+            return this._widgetCanvas.devicePixelRatio;
-            size = size * this._widgetCanvas.canvas.scaleFactor / (float)this._widgetCanvas.pixelRatio;
+            size = size * this._widgetCanvas.canvas.scaleFactor / (float)this._widgetCanvas.devicePixelRatio;
             return new Vector2	(Mathf.Round	(size.x), Mathf.Round	(size.y));
         }
     }
         IPointerEnterHandler, IPointerExitHandler {
         static Event _repaintEvent;
 
+        [SerializeField]
+        protected double devicePixelRatioOverride;
+        
         WindowAdapter _windowAdapter;
         Texture _texture;
         Vector2 _lastMouseMove;
             this._lastMouseMove = Input.mousePosition;
         }
 
-        public double pixelRatio {
-            get { return DisplayMetrics.devicePixelRatio; }
+        public double devicePixelRatio {
+            get { return this.devicePixelRatioOverride > 0 ? this.devicePixelRatioOverride : DisplayMetrics.devicePixelRatio; }
         }
 
         protected virtual Dictionary<string, WidgetBuilder> routes {

Samples/UIWidgetSample/TextInput.unity

   m_LocalScale: {x: 0, y: 0, z: 0}
   m_Children:
   - {fileID: 1387978527}
+  - {fileID: 1354314692}
   - {fileID: 1142533064}
   - {fileID: 1399904531}
   m_Father: {fileID: 0}
   m_LocalScale: {x: 1, y: 1, z: 1}
   m_Children: []
   m_Father: {fileID: 304189374}
-  m_RootOrder: 1
+  m_RootOrder: 2
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   m_AnchorMin: {x: 0, y: 1}
   m_AnchorMax: {x: 0, y: 1}
     y: 0
     width: 1
     height: 1
+  devicePixelRatioOverride: 0
 --- !u!222 &1142533066
 CanvasRenderer:
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   m_PrefabAsset: {fileID: 0}
   m_GameObject: {fileID: 1148735784}
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+--- !u!1 &1354314691
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+  m_CorrespondingSourceObject: {fileID: 0}
+  m_PrefabInstance: {fileID: 0}
+  m_PrefabAsset: {fileID: 0}
+  serializedVersion: 6
+  m_Component:
+  - component: {fileID: 1354314692}
+  - component: {fileID: 1354314694}
+  - component: {fileID: 1354314693}
+  m_Layer: 5
+  m_Name: TextInput Override Ratio
+  m_TagString: Untagged
+  m_Icon: {fileID: 0}
+  m_NavMeshLayer: 0
+  m_StaticEditorFlags: 0
+  m_IsActive: 0
+--- !u!224 &1354314692
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+  m_LocalScale: {x: 1, y: 1, z: 1}
+  m_Children: []
+  m_Father: {fileID: 304189374}
+  m_RootOrder: 1
+  m_LocalEulerAnglesHint: {x: 0, y: 0, z: 0}
+  m_AnchorMin: {x: 0, y: 0}
+  m_AnchorMax: {x: 1, y: 1}
+  m_AnchoredPosition: {x: 0, y: 0}
+  m_SizeDelta: {x: 0, y: 0}
+  m_Pivot: {x: 0.5, y: 0.5}
+--- !u!114 &1354314693
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+  m_EditorClassIdentifier: 
+  m_Material: {fileID: 0}
+  m_Color: {r: 1, g: 1, b: 1, a: 1}
+  m_RaycastTarget: 1
+  m_OnCullStateChanged:
+    m_PersistentCalls:
+      m_Calls: []
+    m_TypeName: UnityEngine.UI.MaskableGraphic+CullStateChangedEvent, UnityEngine.UI,
+      Version=1.0.0.0, Culture=neutral, PublicKeyToken=null
+  m_Texture: {fileID: 0}
+  m_UVRect:
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+    x: 0
+    y: 0
+    width: 1
+    height: 1
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+--- !u!222 &1354314694
+CanvasRenderer:
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+  m_PrefabInstance: {fileID: 0}
+  m_PrefabAsset: {fileID: 0}
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+  m_CullTransparentMesh: 0
 --- !u!1 &1387978526
 GameObject:
   m_ObjectHideFlags: 0
     y: 0
     width: 1
     height: 1
+  devicePixelRatioOverride: 0
 --- !u!222 &1387978529
 CanvasRenderer:
   m_ObjectHideFlags: 0
   - {fileID: 1556903570}
   - {fileID: 335487699}
   m_Father: {fileID: 304189374}
-  m_RootOrder: 2
+  m_RootOrder: 3
   m_LocalEulerAnglesHint: {x: 0, y: 0, z: 0}
   m_AnchorMin: {x: 1, y: 1}
   m_AnchorMax: {x: 1, y: 1}

Editor/editor.meta

+fileFormatVersion: 2
+guid: c339d59e8c37a49fdb2a6365764259fd
+folderAsset: yes
+DefaultImporter:
+  externalObjects: {}
+  userData: 
+  assetBundleName: 
+  assetBundleVariant: 

Editor/editor/WidgetCanvasEditor.cs

+using Unity.UIWidgets.engine;
+using UnityEditor;
+using UnityEditor.UI;
+
+namespace Unity.UIWidgets.Editor {
+    [CustomEditor(typeof(WidgetCanvas), true)]
+    [CanEditMultipleObjects]
+    public class WidgetCanvasEditor : RawImageEditor {
+        public override void OnInspectorGUI() {
+            base.OnInspectorGUI();
+            var pixelRatioProperty = this.serializedObject.FindProperty("devicePixelRatioOverride");
+            EditorGUILayout.PropertyField(pixelRatioProperty);
+            this.serializedObject.ApplyModifiedProperties();
+        }
+    }
+}