From e014eaa3c17201a6c74051cba3fb2ad0fdd1c080 Mon Sep 17 00:00:00 2001
From: Seth Fowler <mark.seth.fowler@gmail.com>
Date: Thu, 17 Sep 2015 15:03:31 -0700
Subject: [PATCH] Bug 1194058 (Part 1) - Add Deinterlacer to allow Downscaler
 to work with interlaced images. r=tn

---
 image/Downscaler.cpp | 31 +++++++++++++++++++++++++++++++
 image/Downscaler.h   | 28 ++++++++++++++++++++++++++++
 2 files changed, 59 insertions(+)

diff --git a/image/Downscaler.cpp b/image/Downscaler.cpp
index 24933d79b8c..0700eeb3229 100644
--- a/image/Downscaler.cpp
+++ b/image/Downscaler.cpp
@@ -281,5 +281,36 @@ Downscaler::DownscaleInputLine()
   }
 }
 
+Deinterlacer::Deinterlacer(const nsIntSize& aImageSize)
+  : mImageSize(aImageSize)
+  , mBuffer(MakeUnique<uint8_t[]>(mImageSize.width *
+                                  mImageSize.height *
+                                  sizeof(uint32_t)))
+{ }
+
+uint32_t
+Deinterlacer::RowSize() const
+{
+  return mImageSize.width * sizeof(uint32_t);
+}
+
+uint8_t*
+Deinterlacer::RowBuffer(uint32_t aRow)
+{
+  uint32_t offset = aRow * RowSize();
+  MOZ_ASSERT(offset < mImageSize.width * mImageSize.height * sizeof(uint32_t),
+             "Row is outside of image");
+  return mBuffer.get() + offset;
+}
+
+void
+Deinterlacer::PropagatePassToDownscaler(Downscaler& aDownscaler)
+{
+  for (int32_t row = 0 ; row < mImageSize.height ; ++row) {
+    memcpy(aDownscaler.RowBuffer(), RowBuffer(row), RowSize());
+    aDownscaler.CommitRow();
+  }
+}
+
 } // namespace image
 } // namespace mozilla
diff --git a/image/Downscaler.h b/image/Downscaler.h
index 745d6854ef5..c883d952895 100644
--- a/image/Downscaler.h
+++ b/image/Downscaler.h
@@ -162,6 +162,34 @@ public:
 
 #endif // MOZ_ENABLE_SKIA
 
+/**
+ * Deinterlacer is a utility class to allow Downscaler to work with interlaced
+ * images.
+
+ * Since Downscaler needs to receive rows in top-to-bottom or
+ * bottom-to-top order, it can't natively handle interlaced images, in which the
+ * rows arrive in an interleaved order. Deinterlacer solves this problem by
+ * acting as an intermediate buffer that records decoded rows. Unlike
+ * Downscaler, it allows the rows to be written in arbitrary order. After each
+ * pass, calling PropagatePassToDownscaler() will downscale every buffered row
+ * in a single operation. The rows remain in the buffer, so rows that were
+ * written in one pass will be included in subsequent passes.
+ */
+class Deinterlacer
+{
+public:
+  explicit Deinterlacer(const nsIntSize& aImageSize);
+
+  uint8_t* RowBuffer(uint32_t aRow);
+  void PropagatePassToDownscaler(Downscaler& aDownscaler);
+
+private:
+  uint32_t RowSize() const;
+
+  nsIntSize mImageSize;
+  UniquePtr<uint8_t[]> mBuffer;
+};
+
 } // namespace image
 } // namespace mozilla