perf(WebXR): Unify WebXR scene default physical factors

Updates default WebXR scene factors to standardize across
VR and AR experiences. Factors are selected to scale and
translate the default scene so that VR and AR example datasets
can be viewed comfortably. Previous behavior resulted in
VR models appearing very large and very close to the user's
face, which was particularly uncomfortable in testing on the
HoloLens 2 headset. In updated behavior the examples in
`GeometryViewer` and `WebXRVolume` appear smaller and at a
comfortable distance from the user.

Author: tbirdso

Sources/Rendering/OpenGL/RenderWindow/index.js

@@ -26,14 +26,8 @@ const SCREENSHOT_PLACEHOLDER = {
 };
 
 const DEFAULT_RESET_FACTORS = {
-  vr: {
-    rescaleFactor: 1.0,
-    translateZ: -0.7, // 0.7 m forward from the camera
-  },
-  ar: {
-    rescaleFactor: 0.25, // scale down AR for viewing comfort by default
-    translateZ: -0.5, // 0.5 m forward from the camera
-  },
+  rescaleFactor: 0.25, // isotropic scale factor reduces apparent size of objects
+  translateZ: -1.5, // default translation initializes object in front of camera
 };
 
 function checkRenderTargetSupport(gl, format, type) {
@@ -371,30 +365,10 @@ function vtkOpenGLRenderWindow(publicAPI, model) {
   };
 
   publicAPI.resetXRScene = (
-    inputRescaleFactor = DEFAULT_RESET_FACTORS.vr.rescaleFactor,
-    inputTranslateZ = DEFAULT_RESET_FACTORS.vr.translateZ
+    rescaleFactor = DEFAULT_RESET_FACTORS.rescaleFactor,
+    translateZ = DEFAULT_RESET_FACTORS.translateZ
   ) => {
     // Adjust world-to-physical parameters for different modalities
-    // Default parameter values are for HMD VR
-    let rescaleFactor = inputRescaleFactor;
-    let translateZ = inputTranslateZ;
-
-    const isXrSessionAR = [
-      XrSessionTypes.HmdAR,
-      XrSessionTypes.MobileAR,
-    ].includes(model.xrSessionType);
-    if (
-      isXrSessionAR &&
-      rescaleFactor === DEFAULT_RESET_FACTORS.vr.rescaleFactor
-    ) {
-      // Scale down by default in AR
-      rescaleFactor = DEFAULT_RESET_FACTORS.ar.rescaleFactor;
-    }
-
-    if (isXrSessionAR && translateZ === DEFAULT_RESET_FACTORS.vr.translateZ) {
-      // Default closer to the camera in AR
-      translateZ = DEFAULT_RESET_FACTORS.ar.translateZ;
-    }
 
     const ren = model.renderable.getRenderers()[0];
     ren.resetCamera();
@@ -403,9 +377,9 @@ function vtkOpenGLRenderWindow(publicAPI, model) {
     let physicalScale = camera.getPhysicalScale();
     const physicalTranslation = camera.getPhysicalTranslation();
 
+    const rescaledTranslateZ = translateZ * physicalScale;
     physicalScale /= rescaleFactor;
-    translateZ *= physicalScale;
-    physicalTranslation[2] += translateZ;
+    physicalTranslation[2] += rescaledTranslateZ;
 
     camera.setPhysicalScale(physicalScale);
     camera.setPhysicalTranslation(physicalTranslation);