Fix #156474, #156473: Cycles wrong mipmap with some types of texture coords

Creating a texture coordinate by combining a UV Map with a white noise
texture did not properly handle that one provides derivatives while the
other does not. It would read from wrong or uninitialized stack memory,
now make sure that is zeroed.

Pull Request: https://projects.blender.org/blender/blender/pulls/156596

intern/cycles/scene/svm.cpp

@@ -17,6 +17,7 @@
 #include "scene/svm.h"
 
 #include "util/log.h"
+#include "util/math_float3.h"
 #include "util/progress.h"
 #include "util/queue.h"
 #include "util/task.h"
@@ -470,6 +471,37 @@ void SVMCompiler::add_value_node(const ShaderNode *node,
   add_node(NODE_VALUE_V, value, node->need_derivatives());
 }
 
+void SVMCompiler::stack_zero_incomplete_derivatives(const ShaderNode *node)
+{
+  /* No derivatives in volumes yet. */
+  if (current_type == SHADER_TYPE_VOLUME) {
+    return;
+  }
+  /* Does this node need derivatives but it doesn't have a derivative variation? */
+  const bool incomplete_derivatives = node->need_derivatives() &&
+                                      svm_node_type_with_derivatives(node->shader_node_type()) ==
+                                          node->shader_node_type();
+  if (!incomplete_derivatives) {
+    return;
+  }
+
+  /* Zero derivatives. */
+  for (const ShaderOutput *output : node->outputs) {
+    if (output->stack_offset == SVM_STACK_INVALID) {
+      continue;
+    }
+    const int base_size = stack_size(output->type());
+    if (base_size == 3) {
+      add_value_node(node, zero_float3(), output->stack_offset + 3);
+      add_value_node(node, zero_float3(), output->stack_offset + 6);
+    }
+    else if (base_size == 1) {
+      add_value_node(node, __float_as_int(0.0f), output->stack_offset + 1);
+      add_value_node(node, __float_as_int(0.0f), output->stack_offset + 2);
+    }
+  }
+}
+
 uint SVMCompiler::attribute(ustring name)
 {
   return scene->shader_manager->get_attribute_id(name);
@@ -505,6 +537,7 @@ void SVMCompiler::find_dependencies(ShaderNodeSet &dependencies,
 void SVMCompiler::generate_node(ShaderNode *node, ShaderNodeSet &done)
 {
   node->compile(*this);
+  stack_zero_incomplete_derivatives(node);
   stack_clear_users(node, done);
   stack_clear_temporary(node);
 

intern/cycles/scene/svm.h

@@ -204,6 +204,7 @@ class SVMCompiler {
   int stack_size(SocketType::Type type);
   int stack_size(const ShaderIO *io);
   void stack_clear_users(ShaderNode *node, ShaderNodeSet &done);
+  void stack_zero_incomplete_derivatives(const ShaderNode *node);
 
   /* single closure */
   void find_dependencies(ShaderNodeSet &dependencies,

tests/files/render/image_mipmap/cycles_renders/image_mipmap_incomplete_derivs.png

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:5850c279206d23fa5b4853f0f38ab6002b8241fb55469cc2061596f24cda6e32
+size 18039

tests/files/render/image_mipmap/cycles_renders_osl/image_mipmap_area_light.png

@@ -1,3 +0,0 @@
-version https://git-lfs.github.com/spec/v1
-oid sha256:00a11d46552adca5cc5643b06aab1326d89980d9a797c4d5322b8e90dc53d98a
-size 16956

tests/files/render/image_mipmap/cycles_renders_osl/image_mipmap_transparent_shadow.png

@@ -1,3 +0,0 @@
-version https://git-lfs.github.com/spec/v1
-oid sha256:b01ae1161c2efad0692797b0eac52dcfefa133bd58d08402ca6667b98facb900
-size 24727

tests/files/render/image_mipmap/cycles_renders_osl/image_mipmap_volume.png

@@ -1,3 +0,0 @@
-version https://git-lfs.github.com/spec/v1
-oid sha256:fc78d3fe50060bcaa173a86ace4498b89c7296458ef1e445d28bde169454c557
-size 13595

tests/files/render/image_mipmap/cycles_renders_osl/image_mipmap_world.png

@@ -1,3 +0,0 @@
-version https://git-lfs.github.com/spec/v1
-oid sha256:0e1bb375452be84d1269265a1a7ee999ee0301522b5d0c6805dbb4d31c442dd9
-size 25548

tests/files/render/image_mipmap/image_mipmap_incomplete_derivs.blend

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:c70461f34d78af0f8b7ea53b84d07527d22e4bcb4e3c6142d7d35ed87cf3c7f5
+size 101296

tests/python/cycles_render_tests.py

@@ -51,6 +51,8 @@ BLOCKLIST_OSL_ALL = BLOCKLIST_OSL_LIMITED + [
     'render_passes_.*.blend',
     # OSL can not specify parameters when reading attribute, which we need for stochastic sampling
     'volume_tricubic_interpolation.blend',
+    # Test specifically for how SVM deals with missing derivatives, which OSL has.
+    "image_mipmap_incomplete_derivs.blend"
 ]
 
 BLOCKLIST_OPTIX = [