LibVideo/VP9: Choose whether/how to show new frames using an enum

There are three mutually exclusive frame-showing states:
- Show no new frame, only store the frame as a reference.
- Show a newly decoded frame.
- Show frame from the reference frame store.
Since they are mutually exclusive, using an enum rather than two bools
makes more sense.

Userland/Libraries/LibVideo/VP9/Context.h

@@ -237,17 +237,26 @@ struct PersistentBlockContext {
     u8 segment_id { 0 };
 };
 
+enum class FrameShowMode {
+    CreateAndShowNewFrame,
+    ShowExistingFrame,
+    DoNotShowFrame,
+};
+
 struct FrameContext {
 public:
     u8 profile { 0 };
 
-    bool shows_existing_frame() const { return m_show_existing_frame; }
+    bool shows_a_frame() const { return m_frame_show_mode != FrameShowMode::DoNotShowFrame; }
-    u8 existing_frame_index() const { return m_existing_frame_index; }
+    bool shows_a_new_frame() const { return m_frame_show_mode == FrameShowMode::CreateAndShowNewFrame; }
+    bool shows_existing_frame() const { return m_frame_show_mode == FrameShowMode::ShowExistingFrame; }
+    void set_frame_hidden() { m_frame_show_mode = FrameShowMode::DoNotShowFrame; }
     void set_existing_frame_to_show(u8 index)
     {
-        m_show_existing_frame = true;
+        m_frame_show_mode = FrameShowMode::ShowExistingFrame;
         m_existing_frame_index = index;
     }
+    u8 existing_frame_index() const { return m_existing_frame_index; }
 
     Gfx::Size<u32> size() const { return m_size; }
     ErrorOr<void> set_size(Gfx::Size<u32> size)
@@ -273,7 +282,7 @@ public:
 private:
     friend struct TileContext;
 
-    bool m_show_existing_frame { false };
+    FrameShowMode m_frame_show_mode { FrameShowMode::CreateAndShowNewFrame };
     u8 m_existing_frame_index { 0 };
 
     Gfx::Size<u32> m_size { 0, 0 };

Userland/Libraries/LibVideo/VP9/Decoder.cpp

@@ -69,7 +69,7 @@ DecoderErrorOr<void> Decoder::decode_frame(ReadonlyBytes frame_data)
     // 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)
+    if (frame_context.shows_a_frame())
         TRY(create_video_frame(frame_context));
 
     // 5. The reference frame update process as specified in section 8.10 is invoked.
@@ -79,6 +79,12 @@ DecoderErrorOr<void> Decoder::decode_frame(ReadonlyBytes frame_data)
 
 DecoderErrorOr<void> Decoder::create_video_frame(FrameContext const& frame_context)
 {
+    // (8.9) Output process
+
+    // FIXME: If show_existing_frame is set, output from FrameStore[frame_to_show_map_index] here instead.
+
+    // FIXME: The math isn't entirely accurate to spec. output_uv_size is probably incorrect for certain
+    //        sizes, as the spec seems to prefer that the halved sizes be ceiled.
     u32 decoded_y_width = frame_context.columns() * 8;
     Gfx::Size<u32> output_y_size = frame_context.size();
     auto decoded_uv_width = decoded_y_width >> m_parser->m_subsampling_x;

Userland/Libraries/LibVideo/VP9/Parser.cpp

@@ -104,7 +104,7 @@ DecoderErrorOr<FrameContext> Parser::parse_frame(ReadonlyBytes frame_data)
     TRY(refresh_probs());
 
     m_previous_frame_size = frame_context.size();
-    m_previous_show_frame = m_show_frame;
+    m_previous_show_frame = frame_context.shows_a_frame();
 
     return frame_context;
 }
@@ -171,7 +171,8 @@ DecoderErrorOr<FrameContext> Parser::uncompressed_header()
 
     m_last_frame_type = m_frame_type;
     m_frame_type = TRY(read_frame_type());
-    m_show_frame = TRY_READ(m_bit_stream->read_bit());
+    if (!TRY_READ(m_bit_stream->read_bit()))
+        frame_context.set_frame_hidden();
     m_error_resilient_mode = TRY_READ(m_bit_stream->read_bit());
 
     Gfx::Size<u32> frame_size;
@@ -185,7 +186,7 @@ DecoderErrorOr<FrameContext> Parser::uncompressed_header()
         m_refresh_frame_flags = 0xFF;
         m_frame_is_intra = true;
     } else {
-        m_frame_is_intra = !m_show_frame && TRY_READ(m_bit_stream->read_bit());
+        m_frame_is_intra = !frame_context.shows_a_frame() && TRY_READ(m_bit_stream->read_bit());
 
         if (!m_error_resilient_mode) {
             m_reset_frame_context = TRY_READ(m_bit_stream->read_bits(2));

Userland/Libraries/LibVideo/VP9/Parser.h

@@ -149,7 +149,6 @@ private:
     bool m_loop_filter_delta_enabled { false };
     FrameType m_frame_type { FrameType::KeyFrame };
     FrameType m_last_frame_type { FrameType::KeyFrame };
-    bool m_show_frame { false };
     bool m_error_resilient_mode { false };
     bool m_frame_is_intra { false };
     u8 m_reset_frame_context { 0 };