LibGfx/WebP: Move lossy decoder to its own file

Pure code move (except of removing `static` on the two public functions
in the new header), not behavior change.

There isn't a lot of lossy decoder yet, but it'll make implementing it
more convenient.

No behavior change.

4 files changed, 120 insertions, 81 deletions

diff --git a/Userland/Libraries/LibGfx/CMakeLists.txt b/Userland/Libraries/LibGfx/CMakeLists.txt
index 7af66dafa7..4e88d5f65f 100644
--- a/Userland/Libraries/LibGfx/CMakeLists.txt
+++ b/Userland/Libraries/LibGfx/CMakeLists.txt
@@ -49,6 +49,7 @@ set(SOURCES
     ImageFormats/TGALoader.cpp
     ImageFormats/WebPLoader.cpp
     ImageFormats/WebPLoaderLossless.cpp
+    ImageFormats/WebPLoaderLossy.cpp
     Painter.cpp
     Palette.cpp
     Path.cpp
diff --git a/Userland/Libraries/LibGfx/ImageFormats/WebPLoader.cpp b/Userland/Libraries/LibGfx/ImageFormats/WebPLoader.cpp
index b5cc00e55b..e5b9715d47 100644
--- a/Userland/Libraries/LibGfx/ImageFormats/WebPLoader.cpp
+++ b/Userland/Libraries/LibGfx/ImageFormats/WebPLoader.cpp
@@ -11,11 +11,11 @@
 #include <AK/Vector.h>
 #include <LibGfx/ImageFormats/WebPLoader.h>
 #include <LibGfx/ImageFormats/WebPLoaderLossless.h>
+#include <LibGfx/ImageFormats/WebPLoaderLossy.h>
 #include <LibGfx/Painter.h>
 
 // Overview: https://developers.google.com/speed/webp/docs/compression
 // Container: https://developers.google.com/speed/webp/docs/riff_container
-// Lossy format: https://datatracker.ietf.org/doc/html/rfc6386
 
 namespace Gfx {
 
@@ -55,17 +55,6 @@ struct Chunk {
     ReadonlyBytes data;
 };
 
-struct VP8Header {
-    u8 version;
-    bool show_frame;
-    u32 size_of_first_partition;
-    u32 width;
-    u8 horizontal_scale;
-    u32 height;
-    u8 vertical_scale;
-    ReadonlyBytes lossy_data;
-};
-
 struct VP8XHeader {
     bool has_icc;
     bool has_alpha;
@@ -228,75 +217,6 @@ static ErrorOr<Chunk> decode_webp_advance_chunk(ReadonlyBytes& chunks)
     return chunk;
 }
 
-// https://developers.google.com/speed/webp/docs/riff_container#simple_file_format_lossy
-// https://datatracker.ietf.org/doc/html/rfc6386#section-19 "Annex A: Bitstream Syntax"
-static ErrorOr<VP8Header> decode_webp_chunk_VP8_header(ReadonlyBytes vp8_data)
-{
-    if (vp8_data.size() < 10)
-        return Error::from_string_literal("WebPImageDecoderPlugin: 'VP8 ' chunk too small");
-
-    // FIXME: Eventually, this should probably call into LibVideo/VP8,
-    // and image decoders should move into LibImageDecoders which depends on both LibGfx and LibVideo.
-    // (LibVideo depends on LibGfx, so LibGfx can't depend on LibVideo itself.)
-
-    // https://datatracker.ietf.org/doc/html/rfc6386#section-4 "Overview of Compressed Data Format"
-    // "The decoder is simply presented with a sequence of compressed frames [...]
-    //  The first frame presented to the decompressor is [...] a key frame.  [...]
-    //  [E]very compressed frame has three or more pieces. It begins with an uncompressed data chunk comprising 10 bytes in the case of key frames
-
-    u8 const* data = vp8_data.data();
-
-    // https://datatracker.ietf.org/doc/html/rfc6386#section-9.1 "Uncompressed Data Chunk"
-    u32 frame_tag = data[0] | (data[1] << 8) | (data[2] << 16);
-    bool is_key_frame = (frame_tag & 1) == 0; // https://www.rfc-editor.org/errata/eid5534
-    u8 version = (frame_tag & 0xe) >> 1;
-    bool show_frame = (frame_tag & 0x10) != 0;
-    u32 size_of_first_partition = frame_tag >> 5;
-
-    if (!is_key_frame)
-        return Error::from_string_literal("WebPImageDecoderPlugin: 'VP8 ' chunk not a key frame");
-
-    // FIXME: !show_frame does not make sense in a webp file either, probably?
-
-    u32 start_code = data[3] | (data[4] << 8) | (data[5] << 16);
-    if (start_code != 0x2a019d) // https://www.rfc-editor.org/errata/eid7370
-        return Error::from_string_literal("WebPImageDecoderPlugin: 'VP8 ' chunk invalid start_code");
-
-    // "The scaling specifications for each dimension are encoded as follows.
-    //   0     | No upscaling (the most common case).
-    //   1     | Upscale by 5/4.
-    //   2     | Upscale by 5/3.
-    //   3     | Upscale by 2."
-    // This is a display-time operation and doesn't affect decoding.
-    u16 width_and_horizontal_scale = data[6] | (data[7] << 8);
-    u16 width = width_and_horizontal_scale & 0x3fff;
-    u8 horizontal_scale = width_and_horizontal_scale >> 14;
-
-    u16 heigth_and_vertical_scale = data[8] | (data[9] << 8);
-    u16 height = heigth_and_vertical_scale & 0x3fff;
-    u8 vertical_scale = heigth_and_vertical_scale >> 14;
-
-    dbgln_if(WEBP_DEBUG, "version {}, show_frame {}, size_of_first_partition {}, width {}, horizontal_scale {}, height {}, vertical_scale {}",
-        version, show_frame, size_of_first_partition, width, horizontal_scale, height, vertical_scale);
-
-    return VP8Header { version, show_frame, size_of_first_partition, width, horizontal_scale, height, vertical_scale, vp8_data.slice(10) };
-}
-
-static ErrorOr<NonnullRefPtr<Bitmap>> decode_webp_chunk_VP8_contents(VP8Header const& vp8_header, bool include_alpha_channel)
-{
-    auto bitmap_format = include_alpha_channel ? BitmapFormat::BGRA8888 : BitmapFormat::BGRx8888;
-
-    // Uncomment this to test ALPH decoding for WebP-lossy-with-alpha images while lossy decoding isn't implemented yet.
-#if 0
-    return Bitmap::create(bitmap_format, { vp8_header.width, vp8_header.height });
-#else
-    // FIXME: Implement webp lossy decoding.
-    (void)vp8_header;
-    (void)bitmap_format;
-    return Error::from_string_literal("WebPImageDecoderPlugin: decoding lossy webps not yet implemented");
-#endif
-}
-
 // https://developers.google.com/speed/webp/docs/riff_container#alpha
 static ErrorOr<void> decode_webp_chunk_ALPH(Chunk const& alph_chunk, Bitmap& bitmap)
 {
diff --git a/Userland/Libraries/LibGfx/ImageFormats/WebPLoaderLossy.cpp b/Userland/Libraries/LibGfx/ImageFormats/WebPLoaderLossy.cpp
new file mode 100644
index 0000000000..928cddada0
--- /dev/null
+++ b/Userland/Libraries/LibGfx/ImageFormats/WebPLoaderLossy.cpp
@@ -0,0 +1,87 @@
+/*
+ * Copyright (c) 2023, Nico Weber <thakis@chromium.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <AK/Debug.h>
+#include <AK/Endian.h>
+#include <AK/Format.h>
+#include <AK/MemoryStream.h>
+#include <AK/Vector.h>
+#include <LibGfx/ImageFormats/WebPLoaderLossy.h>
+
+// Lossy format: https://datatracker.ietf.org/doc/html/rfc6386
+
+namespace Gfx {
+
+// https://developers.google.com/speed/webp/docs/riff_container#simple_file_format_lossy
+// https://datatracker.ietf.org/doc/html/rfc6386#section-19 "Annex A: Bitstream Syntax"
+ErrorOr<VP8Header> decode_webp_chunk_VP8_header(ReadonlyBytes vp8_data)
+{
+    if (vp8_data.size() < 10)
+        return Error::from_string_literal("WebPImageDecoderPlugin: 'VP8 ' chunk too small");
+
+    // FIXME: Eventually, this should probably call into LibVideo/VP8,
+    // and image decoders should move into LibImageDecoders which depends on both LibGfx and LibVideo.
+    // (LibVideo depends on LibGfx, so LibGfx can't depend on LibVideo itself.)
+
+    // https://datatracker.ietf.org/doc/html/rfc6386#section-4 "Overview of Compressed Data Format"
+    // "The decoder is simply presented with a sequence of compressed frames [...]
+    //  The first frame presented to the decompressor is [...] a key frame.  [...]
+    //  [E]very compressed frame has three or more pieces. It begins with an uncompressed data chunk comprising 10 bytes in the case of key frames
+
+    u8 const* data = vp8_data.data();
+
+    // https://datatracker.ietf.org/doc/html/rfc6386#section-9.1 "Uncompressed Data Chunk"
+    u32 frame_tag = data[0] | (data[1] << 8) | (data[2] << 16);
+    bool is_key_frame = (frame_tag & 1) == 0; // https://www.rfc-editor.org/errata/eid5534
+    u8 version = (frame_tag & 0xe) >> 1;
+    bool show_frame = (frame_tag & 0x10) != 0;
+    u32 size_of_first_partition = frame_tag >> 5;
+
+    if (!is_key_frame)
+        return Error::from_string_literal("WebPImageDecoderPlugin: 'VP8 ' chunk not a key frame");
+
+    // FIXME: !show_frame does not make sense in a webp file either, probably?
+
+    u32 start_code = data[3] | (data[4] << 8) | (data[5] << 16);
+    if (start_code != 0x2a019d) // https://www.rfc-editor.org/errata/eid7370
+        return Error::from_string_literal("WebPImageDecoderPlugin: 'VP8 ' chunk invalid start_code");
+
+    // "The scaling specifications for each dimension are encoded as follows.
+    //   0     | No upscaling (the most common case).
+    //   1     | Upscale by 5/4.
+    //   2     | Upscale by 5/3.
+    //   3     | Upscale by 2."
+    // This is a display-time operation and doesn't affect decoding.
+    u16 width_and_horizontal_scale = data[6] | (data[7] << 8);
+    u16 width = width_and_horizontal_scale & 0x3fff;
+    u8 horizontal_scale = width_and_horizontal_scale >> 14;
+
+    u16 heigth_and_vertical_scale = data[8] | (data[9] << 8);
+    u16 height = heigth_and_vertical_scale & 0x3fff;
+    u8 vertical_scale = heigth_and_vertical_scale >> 14;
+
+    dbgln_if(WEBP_DEBUG, "version {}, show_frame {}, size_of_first_partition {}, width {}, horizontal_scale {}, height {}, vertical_scale {}",
+        version, show_frame, size_of_first_partition, width, horizontal_scale, height, vertical_scale);
+
+    return VP8Header { version, show_frame, size_of_first_partition, width, horizontal_scale, height, vertical_scale, vp8_data.slice(10) };
+}
+
+ErrorOr<NonnullRefPtr<Bitmap>> decode_webp_chunk_VP8_contents(VP8Header const& vp8_header, bool include_alpha_channel)
+{
+    auto bitmap_format = include_alpha_channel ? BitmapFormat::BGRA8888 : BitmapFormat::BGRx8888;
+
+    // Uncomment this to test ALPH decoding for WebP-lossy-with-alpha images while lossy decoding isn't implemented yet.
+#if 0
+    return Bitmap::create(bitmap_format, { vp8_header.width, vp8_header.height });
+#else
+    // FIXME: Implement webp lossy decoding.
+    (void)vp8_header;
+    (void)bitmap_format;
+    return Error::from_string_literal("WebPImageDecoderPlugin: decoding lossy webps not yet implemented");
+#endif
+}
+
+}
diff --git a/Userland/Libraries/LibGfx/ImageFormats/WebPLoaderLossy.h b/Userland/Libraries/LibGfx/ImageFormats/WebPLoaderLossy.h
new file mode 100644
index 0000000000..fdf19d61a4
--- /dev/null
+++ b/Userland/Libraries/LibGfx/ImageFormats/WebPLoaderLossy.h
@@ -0,0 +1,31 @@
+/*
+ * Copyright (c) 2023, Nico Weber <thakis@chromium.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Span.h>
+#include <AK/Types.h>
+#include <LibGfx/Bitmap.h>
+
+namespace Gfx {
+
+struct VP8Header {
+    u8 version;
+    bool show_frame;
+    u32 size_of_first_partition;
+    u32 width;
+    u8 horizontal_scale;
+    u32 height;
+    u8 vertical_scale;
+    ReadonlyBytes lossy_data;
+};
+
+// Parses the header data in a VP8 chunk. Pass the payload of a `VP8 ` chunk, after the tag and after the tag's data size.
+ErrorOr<VP8Header> decode_webp_chunk_VP8_header(ReadonlyBytes vp8_data);
+
+ErrorOr<NonnullRefPtr<Bitmap>> decode_webp_chunk_VP8_contents(VP8Header const&, bool include_alpha_channel);
+
+}