BLI: Add generic utlity for gathering values with indices

Add new functions to `array_utils` namespace called `gather(..)`.
Versions of `GVArray::materialize_compressed_to_uninitialized(..)` with
threading have been reimplemented locally in multiple geometry node
contexts. The purpose of this patch is therefore to:
 * Assemble these implementations in a single file.
 * Provide a naming convention that is easier to recognize.

Differential Revision: https://developer.blender.org/D15786

2 files changed, 87 insertions, 1 deletions

diff --git a/source/blender/blenlib/BLI_array_utils.hh b/source/blender/blenlib/BLI_array_utils.hh
index cf2f948b0b4..95b3bde10f4 100644
--- a/source/blender/blenlib/BLI_array_utils.hh
+++ b/source/blender/blenlib/BLI_array_utils.hh
@@ -6,6 +6,7 @@
 #include "BLI_generic_virtual_array.hh"
 #include "BLI_index_mask.hh"
 #include "BLI_task.hh"
+#include "BLI_virtual_array.hh"
 
 namespace blender::array_utils {
 
@@ -25,6 +26,7 @@ inline void copy(const Span<T> src,
                  MutableSpan<T> dst,
                  const int64_t grain_size = 4096)
 {
+  BLI_assert(src.size() == dst.size());
   threading::parallel_for(selection.index_range(), grain_size, [&](const IndexRange range) {
     for (const int64_t index : selection.slice(range)) {
       dst[index] = src[index];
@@ -32,4 +34,77 @@ inline void copy(const Span<T> src,
   });
 }
 
+/**
+ * Fill the destination span by gathering indexed values from the `src` array.
+ */
+void gather(const GVArray &src, IndexMask indices, GMutableSpan dst, int64_t grain_size = 4096);
+
+/**
+ * Fill the destination span by gathering indexed values from the `src` array.
+ */
+template<typename T>
+inline void gather(const VArray<T> &src,
+                   const IndexMask indices,
+                   MutableSpan<T> dst,
+                   const int64_t grain_size = 4096)
+{
+  BLI_assert(indices.size() == dst.size());
+  threading::parallel_for(indices.index_range(), grain_size, [&](const IndexRange range) {
+    src.materialize_compressed_to_uninitialized(indices.slice(range), dst.slice(range).data());
+  });
+}
+
+/**
+ * Fill the destination span by gathering indexed values from the `src` array.
+ */
+template<typename T, typename IndexT>
+inline void gather(const Span<T> src,
+                   const IndexMask indices,
+                   MutableSpan<T> dst,
+                   const int64_t grain_size = 4096)
+{
+  BLI_assert(indices.size() == dst.size());
+  threading::parallel_for(indices.index_range(), grain_size, [&](const IndexRange range) {
+    for (const int64_t i : range) {
+      dst[i] = src[indices[i]];
+    }
+  });
+}
+
+/**
+ * Fill the destination span by gathering indexed values from the `src` array.
+ */
+template<typename T, typename IndexT>
+inline void gather(const Span<T> src,
+                   const Span<IndexT> indices,
+                   MutableSpan<T> dst,
+                   const int64_t grain_size = 4096)
+{
+  BLI_assert(indices.size() == dst.size());
+  threading::parallel_for(indices.index_range(), grain_size, [&](const IndexRange range) {
+    for (const int64_t i : range) {
+      dst[i] = src[indices[i]];
+    }
+  });
+}
+
+/**
+ * Fill the destination span by gathering indexed values from the `src` array.
+ */
+template<typename T, typename IndexT>
+inline void gather(const VArray<T> &src,
+                   const Span<IndexT> indices,
+                   MutableSpan<T> dst,
+                   const int64_t grain_size = 4096)
+{
+  BLI_assert(indices.size() == dst.size());
+  devirtualize_varray(src, [&](const auto &src) {
+    threading::parallel_for(indices.index_range(), grain_size, [&](const IndexRange range) {
+      for (const int64_t i : range) {
+        dst[i] = src[indices[i]];
+      }
+    });
+  });
+}
+
 }  // namespace blender::array_utils
diff --git a/source/blender/blenlib/intern/array_utils.cc b/source/blender/blenlib/intern/array_utils.cc
index a0fc8810199..a837d6aceec 100644
--- a/source/blender/blenlib/intern/array_utils.cc
+++ b/source/blender/blenlib/intern/array_utils.cc
@@ -1,7 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0-or-later */
 
 #include "BLI_array_utils.hh"
-#include "BLI_task.hh"
 
 namespace blender::array_utils {
 
@@ -17,4 +16,16 @@ void copy(const GVArray &src,
   });
 }
 
+void gather(const GVArray &src,
+            const IndexMask indices,
+            GMutableSpan dst,
+            const int64_t grain_size)
+{
+  BLI_assert(src.type() == dst.type());
+  BLI_assert(indices.size() == dst.size());
+  threading::parallel_for(indices.index_range(), grain_size, [&](const IndexRange range) {
+    src.materialize_compressed_to_uninitialized(indices.slice(range), dst.slice(range).data());
+  });
+}
+
 }  // namespace blender::array_utils