Light schema and orientation updates

Update hdPrman to correctly transform lights.  The previous work in change 1970330 didn't take into account texture orientation.
This change matches the newly defined USD spec, which matches the OpenEXR environment map conventions.
Currently only the dome light is special-cased with all other light types using the same orient transform.  If we add support for PxrEnvDayLight, that will need to be special-cased as well.

For #938

(Internal change: 2002994)

third_party/renderman-22/plugin/hdPrman/light.cpp

@@ -139,9 +139,7 @@ HdPrmanLight::Sync(HdSceneDelegate *sceneDelegate,
     riley::Riley *riley = context->riley;
 
     // Some lights have parameters that scale the size of the light.
-    // Scale lights by negative -y and -z to account for RenderMan vs USD
-    // light orientation.
-    GfVec3d geomScale(1.0f, -1.0f, -1.0);
+    GfVec3d geomScale(1.0f);
 
     // For simplicity just re-create the light.  In the future we may
     // want to consider adding a path to use the Modify() API in Riley.
@@ -458,6 +456,31 @@ HdPrmanLight::Sync(HdSceneDelegate *sceneDelegate,
     RtMatrix4x4 xf_rt_values[HDPRMAN_MAX_TIME_SAMPLES];
     GfMatrix4d geomMat(1.0);
     geomMat.SetScale(geomScale);
+
+    // adjust orientation to make prman match the USD spec
+    // TODO: Add another orientMat for PxrEnvDayLight when supported
+    GfMatrix4d orientMat(1.0);
+    if (rileyTypeName == us_PxrDomeLight)
+    {
+        // Transform Dome to match OpenEXR spec for environment maps
+        // Rotate -90 X, Rotate 90 Y
+        orientMat = GfMatrix4d(0.0, 0.0, -1.0, 0.0, 
+                               -1.0, 0.0, 0.0, 0.0, 
+                               0.0, 1.0, 0.0, 0.0, 
+                               0.0, 0.0, 0.0, 1.0);
+    }
+    else
+    {
+        // Transform lights to match correct orientation
+        // Scale -1 Z, Rotate 180 Z
+        orientMat = GfMatrix4d(-1.0, 0.0, 0.0, 0.0, 
+                               0.0, -1.0, 0.0, 0.0, 
+                               0.0, 0.0, -1.0, 0.0, 
+                               0.0, 0.0, 0.0, 1.0);
+    }
+
+    geomMat = orientMat * geomMat;
+
     for (size_t i=0; i < xf.count; ++i) {
         xf_rt_values[i] = HdPrman_GfMatrixToRtMatrix(geomMat * xf.values[i]);
     }