Fix Cycles volume render differences with NanoVDB when using linear sampling

The NanoVDB sampling implementation behaves different from dense texture sampling, so this
adds a small offset to the voxel indices to correct for that.
Also removes the need to modify the sampling coordinates by moving all the necessary
transformations into the image transform. See also T81454.

1 files changed, 9 insertions, 4 deletions

diff --git a/intern/cycles/render/image_vdb.cpp b/intern/cycles/render/image_vdb.cpp
index fc2cfe9874e..016bbf7151d 100644
--- a/intern/cycles/render/image_vdb.cpp
+++ b/intern/cycles/render/image_vdb.cpp
@@ -144,8 +144,13 @@ bool VDBImageLoader::load_metadata(ImageMetaData &metadata)
     }
   }
 
+#  ifdef WITH_NANOVDB
+  /* Add small offset for correct sampling between voxels. */
+  Transform texture_to_index = transform_translate(0.5f, 0.5f, 0.5f);
+#  else
   Transform texture_to_index = transform_translate(min.x(), min.y(), min.z()) *
                                transform_scale(dim.x(), dim.y(), dim.z());
+#  endif
 
   metadata.transform_3d = transform_inverse(index_to_object * texture_to_index);
   metadata.use_transform_3d = true;
@@ -159,10 +164,10 @@ bool VDBImageLoader::load_metadata(ImageMetaData &metadata)
 
 bool VDBImageLoader::load_pixels(const ImageMetaData &, void *pixels, const size_t, const bool)
 {
-#if defined(WITH_NANOVDB)
+#ifdef WITH_OPENVDB
+#  ifdef WITH_NANOVDB
   memcpy(pixels, nanogrid.data(), nanogrid.size());
-  return true;
-#elif defined(WITH_OPENVDB)
+#  else
   if (grid->isType<openvdb::FloatGrid>()) {
     openvdb::tools::Dense<float, openvdb::tools::LayoutXYZ> dense(bbox, (float *)pixels);
     openvdb::tools::copyToDense(*openvdb::gridConstPtrCast<openvdb::FloatGrid>(grid), dense);
@@ -202,7 +207,7 @@ bool VDBImageLoader::load_pixels(const ImageMetaData &, void *pixels, const size
     openvdb::tools::Dense<float, openvdb::tools::LayoutXYZ> dense(bbox, (float *)pixels);
     openvdb::tools::copyToDense(*openvdb::gridConstPtrCast<openvdb::MaskGrid>(grid), dense);
   }
-
+#  endif
   return true;
 #else
   (void)pixels;