Fix T64953: Add cryptomatte meta data to file output node.

This change will try to add meta data when using a multilayered open
exr file output node in the compositor. It adds the current scene meta
data and converts existing cryptomatte keys so it follows the
naming that is configured in the file output node.

This change supports the basic use-case where the compositor is
used to output cryptomatte layers with a different naming scheme to
support external compositors. In this case the Multilayered OpenEXR
files are used and the meta data is read from the render result.

Meta data is found when render layer node is connected with the
file output node without any other nodes in between. Redirects and empty
node groups are allowed.

The patch has been verified to work with external compositors.
See https://devtalk.blender.org/t/making-sense-of-cryptomatte-usage-in-third-party-programs/16576/17

See patch for example files.

Reviewed By: Sergey Sharybin

Differential Revision: https://developer.blender.org/D10016

1 files changed, 51 insertions, 14 deletions

diff --git a/source/blender/blenkernel/intern/cryptomatte.cc b/source/blender/blenkernel/intern/cryptomatte.cc
index 1dd71dacc46..7ddc1474e09 100644
--- a/source/blender/blenkernel/intern/cryptomatte.cc
+++ b/source/blender/blenkernel/intern/cryptomatte.cc
@@ -22,6 +22,7 @@
  */
 
 #include "BKE_cryptomatte.h"
+#include "BKE_cryptomatte.hh"
 #include "BKE_image.h"
 #include "BKE_main.h"
 
@@ -43,6 +44,7 @@
 #include <iomanip>
 #include <sstream>
 #include <string>
+#include <string_view>
 
 enum CryptomatteLayerState {
   EMPTY,
@@ -299,15 +301,15 @@ static uint32_t cryptomatte_determine_identifier(const std::string name)
   return BLI_hash_mm3(reinterpret_cast<const unsigned char *>(name.c_str()), name.length(), 0);
 }
 
-static std::string cryptomatte_determine_prefix(const std::string name)
+static void add_render_result_meta_data(RenderResult *render_result,
+                                        const blender::StringRef layer_name,
+                                        const blender::StringRefNull key_name,
+                                        const blender::StringRefNull value)
 {
-  std::stringstream stream;
-  const uint32_t render_pass_identifier = cryptomatte_determine_identifier(name);
-  stream << "cryptomatte/";
-  stream << std::setfill('0') << std::setw(sizeof(uint32_t) * 2) << std::hex
-         << render_pass_identifier;
-  stream << "/";
-  return stream.str();
+  BKE_render_result_stamp_data(
+      render_result,
+      blender::BKE_cryptomatte_meta_data_key(layer_name, key_name).c_str(),
+      value.data());
 }
 
 void BKE_cryptomatte_store_metadata(struct CryptomatteSession *session,
@@ -335,12 +337,47 @@ void BKE_cryptomatte_store_metadata(struct CryptomatteSession *session,
 
   const std::string manifest = layer->manifest_get_string();
   const std::string name = cryptomatte_determine_name(view_layer, cryptomatte_layer_name);
-  const std::string prefix = cryptomatte_determine_prefix(name);
 
   /* Store the meta data into the render result. */
-  BKE_render_result_stamp_data(render_result, (prefix + "name").c_str(), name.c_str());
-  BKE_render_result_stamp_data(render_result, (prefix + "hash").c_str(), "MurmurHash3_32");
-  BKE_render_result_stamp_data(
-      render_result, (prefix + "conversion").c_str(), "uint32_to_float32");
-  BKE_render_result_stamp_data(render_result, (prefix + "manifest").c_str(), manifest.c_str());
+  add_render_result_meta_data(render_result, name, "name", name);
+  add_render_result_meta_data(render_result, name, "hash", "MurmurHash3_32");
+  add_render_result_meta_data(render_result, name, "conversion", "uint32_to_float32");
+  add_render_result_meta_data(render_result, name, "manifest", manifest);
+}
+
+namespace blender {
+
+/* Return the hash of the given cryptomatte layer name.
+ *
+ * The cryptomatte specification limits the hash to 7 characters.
+ * The 7 position limitation solves issues when using cryptomatte together with OpenEXR.
+ * The specification suggests to use the first 7 chars of the hashed layer_name.
+ */
+static std::string cryptomatte_layer_name_hash(const StringRef layer_name)
+{
+  std::stringstream stream;
+  const uint32_t render_pass_identifier = cryptomatte_determine_identifier(layer_name);
+  stream << std::setfill('0') << std::setw(sizeof(uint32_t) * 2) << std::hex
+         << render_pass_identifier;
+  return stream.str().substr(0, 7);
+}
+
+std::string BKE_cryptomatte_meta_data_key(const StringRef layer_name, const StringRefNull key_name)
+{
+  return "cryptomatte/" + cryptomatte_layer_name_hash(layer_name) + "/" + key_name;
 }
+
+/* Extracts the cryptomatte name from a render pass name.
+ *
+ * Example: A render pass could be named `CryptoObject00`. This
+ *   function would remove the trailing digits and return `CryptoObject`. */
+StringRef BKE_cryptomatte_extract_layer_name(const StringRef render_pass_name)
+{
+  int64_t last_token = render_pass_name.size();
+  while (last_token > 0 && std::isdigit(render_pass_name[last_token - 1])) {
+    last_token -= 1;
+  }
+  return render_pass_name.substr(0, last_token);
+}
+
+}  // namespace blender