diff --git a/src/base/geometry.cpp b/src/base/geometry.cpp
index 2ef0cd85..d715fc25 100644
--- a/src/base/geometry.cpp
+++ b/src/base/geometry.cpp
@@ -128,7 +128,7 @@ void Geometry::_process_shape(
 
         // emplace instance here since we need to know the opaque property
         _accel.emplace_back(*mesh.resource, object_to_world, visible, false);
-                            //(properties & Shape::property_flag_maybe_non_opaque) == 0u);
+        //(properties & Shape::property_flag_maybe_non_opaque) == 0u);
 
         auto light_tag = 0u;
         auto medium_tag = 0u;
@@ -201,14 +201,14 @@ Var<Hit> Geometry::trace_closest(const Var<Ray> &ray) const noexcept {
                 $if(it->shape().maybe_non_opaque() & it->shape().has_surface()) {
                     PolymorphicCall<Surface::Closure> call;
                     _pipeline.surfaces().dispatch(it->shape().surface_tag(), [&](auto surface) noexcept {
-                        $if(surface->maybe_non_opaque()) {
+                        if(surface->maybe_non_opaque()) {
                             // TODO: pass the correct time
                             surface->closure(call, *it, _pipeline.spectrum()->sample(.5f), -ray->direction(), 1.f, 0.f);
-                        };
+                        } else {
+                            compute::unreachable();
+                        }
                     });
-                    auto u1 = xxhash32(as<uint3>(ray->origin()));
-                    auto u2 = xxhash32(as<uint3>(ray->direction()));
-                    auto u = xxhash32(make_uint2(u1, u2)) * 0x1p-32f;
+                    auto u = xxhash32(make_uint4(hit.inst, hit.prim, compute::as<uint2>(hit.bary))) * 0x1p-32f;
                     call.execute([&](const Surface::Closure *closure) noexcept {
                         // apply opacity map
                         auto alpha_skip = def(false);
@@ -243,14 +243,14 @@ Var<bool> Geometry::trace_any(const Var<Ray> &ray) const noexcept {
                 $if(it->shape().maybe_non_opaque() & it->shape().has_surface()) {
                     PolymorphicCall<Surface::Closure> call;
                     _pipeline.surfaces().dispatch(it->shape().surface_tag(), [&](auto surface) noexcept {
-                        $if(surface->maybe_non_opaque()) {
+                        if(surface->maybe_non_opaque()) {
                             // TODO: pass the correct time
                             surface->closure(call, *it, _pipeline.spectrum()->sample(.5f), -ray->direction(), 1.f, 0.f);
-                        };
+                        } else {
+                            compute::unreachable();
+                        }
                     });
-                    auto u1 = xxhash32(as<uint3>(ray->origin()));
-                    auto u2 = xxhash32(as<uint3>(ray->direction()));
-                    auto u = xxhash32(make_uint2(u1, u2)) * 0x1p-32f;
+                    auto u = xxhash32(make_uint4(hit.inst, hit.prim, compute::as<uint2>(hit.bary))) * 0x1p-32f;
                     call.execute([&](const Surface::Closure *closure) noexcept {
                         // apply opacity map
                         auto alpha_skip = def(false);