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, 59 insertions, 0 deletions

diff --git a/source/blender/blenkernel/BKE_cryptomatte.hh b/source/blender/blenkernel/BKE_cryptomatte.hh
new file mode 100644
index 00000000000..892f228187e
--- /dev/null
+++ b/source/blender/blenkernel/BKE_cryptomatte.hh
@@ -0,0 +1,59 @@
+/*
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * The Original Code is Copyright (C) 2020 Blender Foundation.
+ * All rights reserved.
+ */
+
+/** \file
+ * \ingroup bke
+ */
+
+#pragma once
+
+#include <string>
+
+#include "BLI_string_ref.hh"
+
+namespace blender {
+
+/* Format to a cryptomatte meta data key.
+ *
+ * Cryptomatte stores meta data. The keys are formatted containing a hash that
+ * is generated from its layer name.
+ *
+ * The output of this function is:
+ * 'cryptomatte/{hash of layer_name}/{key_name}'.
+ */
+std::string BKE_cryptomatte_meta_data_key(const StringRef layer_name,
+                                          const StringRefNull key_name);
+
+/* Extract the cryptomatte layer name from the given `render_pass_name`.
+ *
+ * Cryptomatte passes are formatted with a trailing number for storing multiple samples that belong
+ * to the same cryptomatte layer. This function would remove the trailing numbers to determine the
+ * cryptomatte layer name.
+ *
+ * # Example
+ *
+ * A render_pass_name could be 'View Layer.CryptoMaterial02'. The cryptomatte layer would be 'View
+ * Layer.CryptoMaterial'.
+ *
+ * NOTE: The return type is a substring of `render_pass_name` and therefore cannot outlive the
+ * `render_pass_name` internal data.
+ */
+StringRef BKE_cryptomatte_extract_layer_name(const StringRef render_pass_name);
+
+}  // namespace blender