Fix non-finite tangent in Cycles with missing UV map

Was causing calculation issues later on in the kernel.

This change catches the most obvious case: missing attribute. The old
code was trying to set tangent to 0, but because it was transformed as
a normal it got converted to non-finite value. This change makes it so
that no transform is involved and 0 is written directly to the SVM
stack.

To cover all cases it will require using safe_normalize() in this node
and in the normal transform function. This is more involved change from
performance point of view, would be nice to verify whether we really want
to go this route.

I've left asserts in the BSDF allocation functions. Don't have strong
connection to them, but think they are handy and are not different from
having an assert in the path radiance checks.

Differential Revision: https://developer.blender.org/D11235

2 files changed, 10 insertions, 3 deletions

diff --git a/intern/cycles/kernel/closure/alloc.h b/intern/cycles/kernel/closure/alloc.h
index 5b74a868e72..99a5a675976 100644
--- a/intern/cycles/kernel/closure/alloc.h
+++ b/intern/cycles/kernel/closure/alloc.h
@@ -57,6 +57,8 @@ ccl_device ccl_addr_space void *closure_alloc_extra(ShaderData *sd, int size)
 
 ccl_device_inline ShaderClosure *bsdf_alloc(ShaderData *sd, int size, float3 weight)
 {
+  kernel_assert(isfinite3_safe(weight));
+
   const float sample_weight = fabsf(average(weight));
 
   /* Use comparison this way to help dealing with non-finite weight: if the average is not finite
@@ -81,6 +83,8 @@ ccl_device_inline ShaderClosure *bsdf_alloc_osl(ShaderData *sd,
                                                 float3 weight,
                                                 void *data)
 {
+  kernel_assert(isfinite3_safe(weight));
+
   const float sample_weight = fabsf(average(weight));
 
   /* Use comparison this way to help dealing with non-finite weight: if the average is not finite
diff --git a/intern/cycles/kernel/svm/svm_tex_coord.h b/intern/cycles/kernel/svm/svm_tex_coord.h
index 4fe940f1a67..fc46bb584be 100644
--- a/intern/cycles/kernel/svm/svm_tex_coord.h
+++ b/intern/cycles/kernel/svm/svm_tex_coord.h
@@ -370,10 +370,13 @@ ccl_device void svm_node_tangent(KernelGlobals *kg, ShaderData *sd, float *stack
 
   if (direction_type == NODE_TANGENT_UVMAP) {
     /* UV map */
-    if (desc.offset == ATTR_STD_NOT_FOUND)
-      tangent = make_float3(0.0f, 0.0f, 0.0f);
-    else
+    if (desc.offset == ATTR_STD_NOT_FOUND) {
+      stack_store_float3(stack, tangent_offset, zero_float3());
+      return;
+    }
+    else {
       tangent = attribute_value;
+    }
   }
   else {
     /* radial */