LibVideo/VP9: Use a struct for block context to keep between frames

There are three fields that we need to store from FrameBlockContext to
keep between frames, which are used to parse for those same fields for
the next frame.

Userland/Libraries/LibVideo/VP9/Context.h

@@ -93,6 +93,39 @@ public:
         return m_storage[index_at(row, column)];
     }
 
+    template<typename OtherT>
+    ErrorOr<void> try_resize_to_match_other_vector2d(Vector2D<OtherT> const& other)
+    {
+        return try_resize(other.height(), other.width());
+    }
+
+    template<typename OtherT, typename Function>
+    void copy_to(Vector2D<OtherT>& other, Function function)
+    {
+        VERIFY(width() <= other.width());
+        VERIFY(height() <= other.height());
+        for (u32 row = 0; row < height(); row++) {
+            for (u32 column = 0; column < width(); column++)
+                other.at(row, column) = function(at(row, column));
+        }
+    }
+
+    void copy_to(Vector2D<T>& other)
+    {
+        VERIFY(width() <= other.width());
+        VERIFY(height() <= other.height());
+        for (u32 row = 0; row < height(); row++) {
+            auto other_index = other.index_at(row, 0);
+            AK::TypedTransfer<T>::copy(&m_storage[index_at(row, 0)], &other[other_index], width());
+        }
+    }
+
+    void reset()
+    {
+        for (size_t i = 0; i < size(); i++)
+            m_storage[i] = T();
+    }
+
 private:
     u32 m_height { 0 };
     u32 m_width { 0 };
@@ -124,4 +157,25 @@ struct FrameBlockContext {
     u8 segment_id { 0 };
 };
 
+// Block context that is kept between frames until explictly cleared.
+struct PersistentBlockContext {
+    PersistentBlockContext()
+        : available(false)
+    {
+    }
+
+    PersistentBlockContext(FrameBlockContext const& frame_context)
+        : available(frame_context.is_available)
+        , ref_frames(frame_context.ref_frames)
+        , primary_motion_vector_pair(frame_context.primary_motion_vector_pair())
+        , segment_id(frame_context.segment_id)
+    {
+    }
+
+    bool available { false };
+    ReferenceFramePair ref_frames { ReferenceFrameType::None, ReferenceFrameType::None };
+    MotionVectorPair primary_motion_vector_pair {};
+    u8 segment_id { 0 };
+};
+
 }

Userland/Libraries/LibVideo/VP9/Decoder.cpp

@@ -66,14 +66,7 @@ DecoderErrorOr<void> Decoder::decode_frame(ReadonlyBytes frame_data)
     // − show_existing_frame is equal to 0,
     // − segmentation_enabled is equal to 1,
     // − segmentation_update_map is equal to 1.
-    if (!m_parser->m_show_existing_frame && m_parser->m_segmentation_enabled && m_parser->m_segmentation_update_map) {
-        for (auto row = 0u; row < m_parser->m_mi_rows; row++) {
-            for (auto column = 0u; column < m_parser->m_mi_cols; column++) {
-                auto index = index_from_row_and_column(row, column, m_parser->m_mi_rows);
-                m_parser->m_prev_segment_ids[index] = m_parser->m_frame_block_contexts[index].segment_id;
-            }
-        }
-    }
+    // This is handled by update_reference_frames.
 
     // 4. The output process as specified in section 8.9 is invoked.
     if (m_parser->m_show_frame)
@@ -1808,21 +1801,24 @@ DecoderErrorOr<void> Decoder::update_reference_frames()
 
     // 2. If show_existing_frame is equal to 0, the following applies:
     if (!m_parser->m_show_existing_frame) {
+        DECODER_TRY_ALLOC(m_parser->m_previous_block_contexts.try_resize_to_match_other_vector2d(m_parser->m_frame_block_contexts));
         // − PrevRefFrames[ row ][ col ][ list ] is set equal to RefFrames[ row ][ col ][ list ] for row = 0..MiRows-1,
         // for col = 0..MiCols-1, for list = 0..1.
         // − PrevMvs[ row ][ col ][ list ][ comp ] is set equal to Mvs[ row ][ col ][ list ][ comp ] for row = 0..MiRows-1,
         // for col = 0..MiCols-1, for list = 0..1, for comp = 0..1.
-        size_t size = m_parser->m_frame_block_contexts.width() * m_parser->m_frame_block_contexts.height();
-        m_parser->m_prev_ref_frames.resize_and_keep_capacity(size);
-        m_parser->m_prev_mvs.resize_and_keep_capacity(size);
-        for (u32 row = 0; row < m_parser->m_frame_block_contexts.height(); row++) {
-            for (u32 column = 0; column < m_parser->m_frame_block_contexts.width(); column++) {
-                auto index = m_parser->m_frame_block_contexts.index_at(row, column);
-                auto context = m_parser->m_frame_block_contexts[index];
-                m_parser->m_prev_ref_frames[index] = context.ref_frames;
-                m_parser->m_prev_mvs[index] = context.primary_motion_vector_pair();
-            }
-        }
+        // And from decode_frame():
+        // - If all of the following conditions are true, PrevSegmentIds[ row ][ col ] is set equal to
+        // SegmentIds[ row ][ col ] for row = 0..MiRows-1, for col = 0..MiCols-1:
+        //   − show_existing_frame is equal to 0,
+        //   − segmentation_enabled is equal to 1,
+        //   − segmentation_update_map is equal to 1.
+        bool keep_segment_ids = !m_parser->m_show_existing_frame && m_parser->m_segmentation_enabled && m_parser->m_segmentation_update_map;
+        m_parser->m_frame_block_contexts.copy_to(m_parser->m_previous_block_contexts, [keep_segment_ids](FrameBlockContext context) {
+            auto persistent_context = PersistentBlockContext(context);
+            if (!keep_segment_ids)
+                persistent_context.segment_id = 0;
+            return persistent_context;
+        });
     }
 
     return {};

Userland/Libraries/LibVideo/VP9/Parser.cpp

@@ -494,9 +494,8 @@ void Parser::setup_past_independence()
             m_feature_enabled[i][j] = false;
         }
     }
+    m_previous_block_contexts.reset(); 
     m_segmentation_abs_or_delta_update = false;
-    m_prev_segment_ids.clear_with_capacity();
-    m_prev_segment_ids.resize_and_keep_capacity(m_mi_rows * m_mi_cols);
     m_loop_filter_delta_enabled = true;
     m_loop_filter_ref_deltas[IntraFrame] = 1;
     m_loop_filter_ref_deltas[LastFrame] = 0;
@@ -1111,7 +1110,7 @@ u8 Parser::get_segment_id()
     u8 segment = 7;
     for (size_t y = 0; y < ymis; y++) {
         for (size_t x = 0; x < xmis; x++) {
-            segment = min(segment, m_prev_segment_ids[get_image_index(m_mi_row + y, m_mi_col + x)]);
+            segment = min(segment, m_previous_block_contexts.index_at(m_mi_row + y, m_mi_col + x));
         }
     }
     return segment;
@@ -1498,10 +1497,10 @@ void Parser::add_mv_ref_list(u8 ref_list)
 
 void Parser::get_block_mv(u32 candidate_row, u32 candidate_column, u8 ref_list, bool use_prev)
 {
-    auto index = get_image_index(candidate_row, candidate_column);
     if (use_prev) {
-        m_candidate_mv[ref_list] = m_prev_mvs[index][ref_list];
-        m_candidate_frame[ref_list] = m_prev_ref_frames[index][ref_list];
+        auto const& prev_context = m_previous_block_contexts.at(candidate_row, candidate_column);
+        m_candidate_mv[ref_list] = prev_context.primary_motion_vector_pair[ref_list];
+        m_candidate_frame[ref_list] = prev_context.ref_frames[ref_list];
     } else {
         auto const& current_context = m_frame_block_contexts.at(candidate_row, candidate_column);
         m_candidate_mv[ref_list] = current_context.primary_motion_vector_pair()[ref_list];

Userland/Libraries/LibVideo/VP9/Parser.h

@@ -259,7 +259,6 @@ private:
     ReferenceFramePair m_comp_var_ref;
     // FIXME: Use Array<MotionVectorPair, 4> instead.
     Array<Array<MotionVector, 4>, 2> m_block_mvs;
-    Vector<u8> m_prev_segment_ids;
 
     // FIXME: From spec: NOTE – We are using a 2D array to store the SubModes for clarity. It is possible to reduce memory
     //        consumption by only storing one intra mode for each 8x8 horizontal and vertical position, i.e. to use two 1D
@@ -273,8 +272,7 @@ private:
     u8 m_ref_mv_count { 0 };
     MotionVectorPair m_ref_list_mv;
     bool m_use_prev_frame_mvs;
-    Vector<ReferenceFramePair> m_prev_ref_frames;
-    Vector<MotionVectorPair> m_prev_mvs;
+    Vector2D<PersistentBlockContext> m_previous_block_contexts;
     // Indexed by ReferenceFrame enum.
     u8 m_mode_context[4] { INVALID_CASE };