[Hdrp] Fix issue with linking FoV to physical camera

com.unity.render-pipelines.high-definition/CHANGELOG.md

@@ -62,6 +62,7 @@ The version number for this package has increased due to a version update of a r
 - Fixed issue when resizing Inspector window that make the DecalProjector editor flickers.
 - Fixed issue in DecalProjector editor when the Inspector window have a too small width: the size appears on 2 lines but the editor not let place for the second one.
 - Fixed issue (null reference in console) when selecting a DensityVolume with rectangle selection.
+- Fixed issue when linking the field of view with the focal length in physical camera
 
 ### Changed
 - Combined occlusion meshes into one to reduce draw calls and state changes with XR single-pass.

com.unity.render-pipelines.high-definition/Editor/RenderPipeline/Camera/HDCameraUI.Drawers.cs

@@ -405,10 +405,14 @@ static void Drawer_PhysicalCamera(SerializedHDCamera p, Editor owner)
                 using (new EditorGUI.PropertyScope(horizontal.rect, focalLengthContent, cam.focalLength))
                 using (var checkScope = new EditorGUI.ChangeCheckScope())
                 {
+                    bool isPhysical = p.projectionMatrixMode.intValue == (int)ProjectionMatrixMode.PhysicalPropertiesBased;
+                    // We need to update the focal length if the camera is physical and the FoV has changed.
+                    bool focalLengthIsDirty = (s_FovChanged && isPhysical);
+
                     float sensorLength = cam.fovAxisMode.intValue == 0 ? cam.sensorSize.vector2Value.y : cam.sensorSize.vector2Value.x;
-                    float focalLengthVal = s_FovChanged ? Camera.FieldOfViewToFocalLength(s_FovLastValue, sensorLength) : cam.focalLength.floatValue;
+                    float focalLengthVal = focalLengthIsDirty ? Camera.FieldOfViewToFocalLength(s_FovLastValue, sensorLength) : cam.focalLength.floatValue;
                     focalLengthVal = EditorGUILayout.FloatField(focalLengthContent, focalLengthVal);
-                    if (checkScope.changed || s_FovChanged)
+                    if (checkScope.changed || focalLengthIsDirty)
                         cam.focalLength.floatValue = focalLengthVal;
                 }