From ebd431d58080a300b266ffec4e87c0e1f457bfd8 Mon Sep 17 00:00:00 2001
From: Weizhen Huang <weizhen@blender.org>
Date: Tue, 6 Jun 2023 13:19:28 +0200
Subject: [PATCH] Fix wrong normal transformation in Vector Transform shader
 node

Normals do not transform the same way as vectors do, see
https://www.pbr-book.org/3ed-2018/Geometry_and_Transformations/Applying_Transformations
---
 intern/cycles/kernel/svm/vector_transform.h | 79 ++++++++++++++-------
 1 file changed, 52 insertions(+), 27 deletions(-)

diff --git a/intern/cycles/kernel/svm/vector_transform.h b/intern/cycles/kernel/svm/vector_transform.h
index 2c69e6c7b63..3eb2f7a5207 100644
--- a/intern/cycles/kernel/svm/vector_transform.h
+++ b/intern/cycles/kernel/svm/vector_transform.h
@@ -26,23 +26,31 @@ ccl_device_noinline void svm_node_vector_transform(KernelGlobals kg,
 
   Transform tfm;
   bool is_object = (sd->object != OBJECT_NONE);
-  bool is_direction = (type == NODE_VECTOR_TRANSFORM_TYPE_VECTOR ||
-                       type == NODE_VECTOR_TRANSFORM_TYPE_NORMAL);
+  bool is_normal = (type == NODE_VECTOR_TRANSFORM_TYPE_NORMAL);
+  bool is_direction = (type == NODE_VECTOR_TRANSFORM_TYPE_VECTOR);
 
   /* From world */
   if (from == NODE_VECTOR_TRANSFORM_CONVERT_SPACE_WORLD) {
     if (to == NODE_VECTOR_TRANSFORM_CONVERT_SPACE_CAMERA) {
-      tfm = kernel_data.cam.worldtocamera;
-      if (is_direction)
-        in = transform_direction(&tfm, in);
-      else
-        in = transform_point(&tfm, in);
+      if (is_normal) {
+        tfm = kernel_data.cam.cameratoworld;
+        in = normalize(transform_direction_transposed(&tfm, in));
+      }
+      else {
+        tfm = kernel_data.cam.worldtocamera;
+        in = is_direction ? transform_direction(&tfm, in) : transform_point(&tfm, in);
+      }
     }
     else if (to == NODE_VECTOR_TRANSFORM_CONVERT_SPACE_OBJECT && is_object) {
-      if (is_direction)
+      if (is_normal) {
+        object_inverse_normal_transform(kg, sd, &in);
+      }
+      else if (is_direction) {
         object_inverse_dir_transform(kg, sd, &in);
-      else
+      }
+      else {
         object_inverse_position_transform(kg, sd, &in);
+      }
     }
   }
 
@@ -51,17 +59,25 @@ ccl_device_noinline void svm_node_vector_transform(KernelGlobals kg,
     if (to == NODE_VECTOR_TRANSFORM_CONVERT_SPACE_WORLD ||
         to == NODE_VECTOR_TRANSFORM_CONVERT_SPACE_OBJECT)
     {
-      tfm = kernel_data.cam.cameratoworld;
-      if (is_direction)
-        in = transform_direction(&tfm, in);
-      else
-        in = transform_point(&tfm, in);
+      if (is_normal) {
+        tfm = kernel_data.cam.worldtocamera;
+        in = normalize(transform_direction_transposed(&tfm, in));
+      }
+      else {
+        tfm = kernel_data.cam.cameratoworld;
+        in = is_direction ? transform_direction(&tfm, in) : transform_point(&tfm, in);
+      }
     }
     if (to == NODE_VECTOR_TRANSFORM_CONVERT_SPACE_OBJECT && is_object) {
-      if (is_direction)
+      if (is_normal) {
+        object_inverse_normal_transform(kg, sd, &in);
+      }
+      else if (is_direction) {
         object_inverse_dir_transform(kg, sd, &in);
-      else
+      }
+      else {
         object_inverse_position_transform(kg, sd, &in);
+      }
     }
   }
 
@@ -71,24 +87,33 @@ ccl_device_noinline void svm_node_vector_transform(KernelGlobals kg,
          to == NODE_VECTOR_TRANSFORM_CONVERT_SPACE_CAMERA) &&
         is_object)
     {
-      if (is_direction)
+      if (is_normal) {
+        object_normal_transform(kg, sd, &in);
+      }
+      else if (is_direction) {
         object_dir_transform(kg, sd, &in);
-      else
+      }
+      else {
         object_position_transform(kg, sd, &in);
+      }
     }
     if (to == NODE_VECTOR_TRANSFORM_CONVERT_SPACE_CAMERA) {
-      tfm = kernel_data.cam.worldtocamera;
-      if (is_direction)
-        in = transform_direction(&tfm, in);
-      else
-        in = transform_point(&tfm, in);
+      if (is_normal) {
+        tfm = kernel_data.cam.cameratoworld;
+        in = normalize(transform_direction_transposed(&tfm, in));
+      }
+      else {
+        tfm = kernel_data.cam.worldtocamera;
+        if (is_direction) {
+          in = transform_direction(&tfm, in);
+        }
+        else {
+          in = transform_point(&tfm, in);
+        }
+      }
     }
   }
 
-  /* Normalize Normal */
-  if (type == NODE_VECTOR_TRANSFORM_TYPE_NORMAL)
-    in = normalize(in);
-
   /* Output */
   if (stack_valid(vector_out)) {
     stack_store_float3(stack, vector_out, in);