Fix #111588: Cycles: Vector displacement with adaptive subdiv breaks normal

The compact form of the differential is not enough here, we need to store
and use the full vectors for bump evaluation.

Pull Request: https://projects.blender.org/blender/blender/pulls/112987

intern/cycles/kernel/svm/bump.h

@@ -30,6 +30,10 @@ ccl_device_noinline void svm_node_enter_bump_eval(KernelGlobals kg,
 
     sd->P = P;
     sd->dP = differential_make_compact(dP);
+
+    /* Save the full differential, the compact form isn't enough for svm_node_set_bump. */
+    stack_store_float3(stack, offset + 4, dP.dx);
+    stack_store_float3(stack, offset + 7, dP.dy);
   }
 }
 

intern/cycles/kernel/svm/displace.h

@@ -15,6 +15,9 @@ ccl_device_noinline void svm_node_set_bump(KernelGlobals kg,
                                            ccl_private float *stack,
                                            uint4 node)
 {
+  uint out_offset, bump_state_offset, dummy;
+  svm_unpack_node_uchar4(node.w, &out_offset, &bump_state_offset, &dummy, &dummy);
+
 #ifdef __RAY_DIFFERENTIALS__
   IF_KERNEL_NODES_FEATURE(BUMP)
   {
@@ -25,7 +28,16 @@ ccl_device_noinline void svm_node_set_bump(KernelGlobals kg,
     float3 normal_in = stack_valid(normal_offset) ? stack_load_float3(stack, normal_offset) :
                                                     sd->N;
 
-    differential3 dP = differential_from_compact(sd->Ng, sd->dP);
+    /* If we have saved bump state, read the full differential from there.
+     * Just using the compact form in those cases leads to incorrect normals (see #111588). */
+    differential3 dP;
+    if (bump_state_offset == SVM_STACK_INVALID) {
+      dP = differential_from_compact(sd->Ng, sd->dP);
+    }
+    else {
+      dP.dx = stack_load_float3(stack, bump_state_offset + 4);
+      dP.dy = stack_load_float3(stack, bump_state_offset + 7);
+    }
 
     if (use_object_space) {
       object_inverse_normal_transform(kg, sd, &normal_in);
@@ -72,10 +84,10 @@ ccl_device_noinline void svm_node_set_bump(KernelGlobals kg,
       object_normal_transform(kg, sd, &normal_out);
     }
 
-    stack_store_float3(stack, node.w, normal_out);
+    stack_store_float3(stack, out_offset, normal_out);
   }
   else {
-    stack_store_float3(stack, node.w, zero_float3());
+    stack_store_float3(stack, out_offset, zero_float3());
   }
 #endif
 }

intern/cycles/kernel/svm/types.h

@@ -13,7 +13,7 @@ CCL_NAMESPACE_BEGIN
 /* SVM stack offsets with this value indicate that it's not on the stack */
 #define SVM_STACK_INVALID 255
 
-#define SVM_BUMP_EVAL_STATE_SIZE 4
+#define SVM_BUMP_EVAL_STATE_SIZE 10
 
 /* Nodes */
 

intern/cycles/scene/shader_nodes.cpp

@@ -6726,16 +6726,17 @@ void BumpNode::compile(SVMCompiler &compiler)
   ShaderOutput *normal_out = output("Normal");
 
   /* pack all parameters in the node */
-  compiler.add_node(NODE_SET_BUMP,
-                    compiler.encode_uchar4(compiler.stack_assign_if_linked(normal_in),
-                                           compiler.stack_assign(distance_in),
-                                           invert,
-                                           use_object_space),
-                    compiler.encode_uchar4(compiler.stack_assign(center_in),
-                                           compiler.stack_assign(dx_in),
-                                           compiler.stack_assign(dy_in),
-                                           compiler.stack_assign(strength_in)),
-                    compiler.stack_assign(normal_out));
+  compiler.add_node(
+      NODE_SET_BUMP,
+      compiler.encode_uchar4(compiler.stack_assign_if_linked(normal_in),
+                             compiler.stack_assign(distance_in),
+                             invert,
+                             use_object_space),
+      compiler.encode_uchar4(compiler.stack_assign(center_in),
+                             compiler.stack_assign(dx_in),
+                             compiler.stack_assign(dy_in),
+                             compiler.stack_assign(strength_in)),
+      compiler.encode_uchar4(compiler.stack_assign(normal_out), compiler.get_bump_state_offset()));
 }
 
 void BumpNode::compile(OSLCompiler &compiler)

intern/cycles/scene/svm.cpp

@@ -163,6 +163,7 @@ SVMCompiler::SVMCompiler(Scene *scene) : scene(scene)
   current_graph = NULL;
   background = false;
   mix_weight_offset = SVM_STACK_INVALID;
+  bump_state_offset = SVM_STACK_INVALID;
   compile_failed = false;
 
   /* This struct has one entry for every node, in order of ShaderNodeType definition. */
@@ -784,9 +785,8 @@ void SVMCompiler::compile_type(Shader *shader, ShaderGraph *graph, ShaderType ty
   }
 
   /* for the bump shader we need add a node to store the shader state */
-  bool need_bump_state = (type == SHADER_TYPE_BUMP) &&
-                         (shader->get_displacement_method() == DISPLACE_BOTH);
-  int bump_state_offset = SVM_STACK_INVALID;
+  const bool need_bump_state = (type == SHADER_TYPE_BUMP) &&
+                               (shader->get_displacement_method() == DISPLACE_BOTH);
   if (need_bump_state) {
     bump_state_offset = stack_find_offset(SVM_BUMP_EVAL_STATE_SIZE);
     add_node(NODE_ENTER_BUMP_EVAL, bump_state_offset);
@@ -846,6 +846,7 @@ void SVMCompiler::compile_type(Shader *shader, ShaderGraph *graph, ShaderType ty
   /* add node to restore state after bump shader has finished */
   if (need_bump_state) {
     add_node(NODE_LEAVE_BUMP_EVAL, bump_state_offset);
+    bump_state_offset = SVM_STACK_INVALID;
   }
 
   /* if compile failed, generate empty shader */

intern/cycles/scene/svm.h

@@ -106,6 +106,10 @@ class SVMCompiler {
   {
     return mix_weight_offset;
   }
+  uint get_bump_state_offset()
+  {
+    return bump_state_offset;
+  }
 
   ShaderType output_type()
   {
@@ -222,6 +226,7 @@ class SVMCompiler {
   Stack active_stack;
   int max_stack_use;
   uint mix_weight_offset;
+  uint bump_state_offset;
   bool compile_failed;
 };