Fix viewport icon rendering on high DPI devices (#1006)

* Clarify ViewportWorldToScreen being in widget space and add DeviceScalingFactor

* -Fix viewport icons being draw wrong on high DPI displays
-Fix loading viewport icons from absolute paths, which

* Address review feedback, fix build

Code/Framework/AzManipulatorTestFramework/Include/AzManipulatorTestFramework/ViewportInteraction.h

@@ -41,6 +41,7 @@ namespace AzManipulatorTestFramework
         AZStd::optional<AZ::Vector3> ViewportScreenToWorld(const AzFramework::ScreenPoint& screenPosition, float depth) override;
         AZStd::optional<AzToolsFramework::ViewportInteraction::ProjectedViewportRay> ViewportScreenToWorldRay(
             const AzFramework::ScreenPoint& screenPosition) override;
+        float DeviceScalingFactor() override;
     private:
         // ViewportInteractionRequestBus ...
         bool GridSnappingEnabled();

Code/Framework/AzManipulatorTestFramework/Source/ViewportInteraction.cpp

@@ -127,4 +127,9 @@ namespace AzManipulatorTestFramework
     {
         return {};
     }
-} // namespace AzManipulatorTestFramework
+
+    float ViewportInteraction::DeviceScalingFactor()
+    {
+        return 1.0f;
+    }
+}// namespace AzManipulatorTestFramework

Code/Framework/AzToolsFramework/AzToolsFramework/Viewport/ViewportMessages.h

@@ -165,15 +165,18 @@ namespace AzToolsFramework
             virtual bool AngleSnappingEnabled() = 0;
             /// Return the angle snapping/step size.
             virtual float AngleStep() = 0;
-            /// Transform a point in world space to screen space coordinates.
+            /// Transform a point in world space to screen space coordinates in Qt Widget space.
+            /// Multiply by DeviceScalingFactor to get the position in viewport pixel space.
             virtual AzFramework::ScreenPoint ViewportWorldToScreen(const AZ::Vector3& worldPosition) = 0;
-            /// Transform a point in screen space coordinates to a vector in world space based on clip space depth.
+            /// Transform a point from Qt widget screen space to world space based on the given clip space depth.
             /// Depth specifies a relative camera depth to project in the range of [0.f, 1.f].
             /// Returns the world space position if successful.
             virtual AZStd::optional<AZ::Vector3> ViewportScreenToWorld(const AzFramework::ScreenPoint& screenPosition, float depth) = 0;
             /// Casts a point in screen space to a ray in world space originating from the viewport camera frustum's near plane.
             /// Returns a ray containing the ray's origin and a direction normal, if successful.
             virtual AZStd::optional<ProjectedViewportRay> ViewportScreenToWorldRay(const AzFramework::ScreenPoint& screenPosition) = 0;
+            /// Gets the DPI scaling factor that translates Qt widget space into viewport pixel space.
+            virtual float DeviceScalingFactor() = 0;
 
         protected:
             ~ViewportInteractionRequests() = default;

Code/Sandbox/Editor/RenderViewport.h

@@ -200,6 +200,7 @@ public:
     {
         return {};
     }
+    float DeviceScalingFactor() override { return 1.0f; }
 
     // AzToolsFramework::ViewportFreezeRequestBus
     bool IsViewportInputFrozen() override;