Use a predictable RNG when adding noise to low-bitrate images.

The recovery code assumes that encoding a given frame from the
same data will always give the same output; it always encodes frame 0
again to set things up properly and if that frame is a different size
to the previous run everything breaks.

1 files changed, 44 insertions, 0 deletions

diff --git a/src/lib/rng.h b/src/lib/rng.h
new file mode 100644
index 000000000..f3349ce9b
--- /dev/null
+++ b/src/lib/rng.h
@@ -0,0 +1,44 @@
+/*
+    Copyright (C) 2020 Carl Hetherington <cth@carlh.net>
+
+    This file is part of DCP-o-matic.
+
+    DCP-o-matic 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.
+
+    DCP-o-matic 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 DCP-o-matic.  If not, see <http://www.gnu.org/licenses/>.
+
+*/
+
+
+#include <stdint.h>
+
+
+namespace dcpomatic {
+
+
+/** @class  RNG
+ *  @brief  Linear-feedback random number generator
+ */
+class RNG
+{
+public:
+	RNG (int32_t seed);
+
+	int32_t get ();
+
+private:
+	uint32_t _state;
+};
+
+
+}
+