LibGfx: Use ZlibCompressor for compressing PNG files

Previously we were hand-writing all the Zlib and raw Deflated data
structures here, but now PNGs will be compressed using ZlibCompressor
which will actually try to compress something! :^)

Note that we don't do any filtering that should help compress data even
more, but even now the results are pretty good:

- screenshots of my Serenity desktop are take now about 55 KiB, where
  previously it was 3 MiB.
- re-encoding NASA photo of the Earth[1] to PNG shows a 2x improvement
  (34.3 MiB -> 16.5 MiB).

[1]: https://commons.wikimedia.org/wiki/File:The_Blue_Marble_(remastered).jpg

Userland/Libraries/LibGfx/PNGWriter.cpp

@@ -8,6 +8,7 @@
 
 #include <AK/Concepts.h>
 #include <AK/String.h>
+#include <LibCompress/Zlib.h>
 #include <LibCrypto/Checksum/CRC32.h>
 #include <LibGfx/Bitmap.h>
 #include <LibGfx/PNGWriter.h>
@@ -46,23 +47,6 @@ private:
     String m_type;
 };
 
-class NonCompressibleBlock {
-public:
-    void finalize(PNGChunk&);
-    void add_byte_to_block(u8 data, PNGChunk&);
-
-    u16 adler_s1() const { return m_adler_s1; }
-    u16 adler_s2() const { return m_adler_s2; }
-
-private:
-    void add_block_to_chunk(PNGChunk&, bool);
-    void update_adler(u8);
-    bool full() { return m_non_compressible_data.size() == 65535; }
-    Vector<u8> m_non_compressible_data;
-    u16 m_adler_s1 { 1 };
-    u16 m_adler_s2 { 0 };
-};
-
 PNGChunk::PNGChunk(String type)
     : m_type(move(type))
 {
@@ -118,40 +102,6 @@ void PNGChunk::add_u8(u8 data)
     add(data);
 }
 
-void NonCompressibleBlock::add_byte_to_block(u8 data, PNGChunk& chunk)
-{
-    m_non_compressible_data.append(data);
-    update_adler(data);
-    if (full()) {
-        add_block_to_chunk(chunk, false);
-        m_non_compressible_data.clear_with_capacity();
-    }
-}
-
-void NonCompressibleBlock::add_block_to_chunk(PNGChunk& png_chunk, bool last)
-{
-    png_chunk.add_u8(last);
-
-    u16 len = m_non_compressible_data.size();
-    u16 nlen = ~len;
-
-    png_chunk.add_as_little_endian(len);
-    png_chunk.add_as_little_endian(nlen);
-
-    png_chunk.add(m_non_compressible_data.data(), m_non_compressible_data.size());
-}
-
-void NonCompressibleBlock::finalize(PNGChunk& chunk)
-{
-    add_block_to_chunk(chunk, true);
-}
-
-void NonCompressibleBlock::update_adler(u8 data)
-{
-    m_adler_s1 = (m_adler_s1 + data) % 65521;
-    m_adler_s2 = (m_adler_s2 + m_adler_s1) % 65521;
-}
-
 void PNGWriter::add_chunk(PNGChunk& png_chunk)
 {
     png_chunk.store_data_length();
@@ -190,27 +140,29 @@ void PNGWriter::add_IDAT_chunk(Gfx::Bitmap const& bitmap)
     PNGChunk png_chunk { "IDAT" };
     png_chunk.reserve(bitmap.size_in_bytes());
 
-    u16 CMF_FLG = 0x81d;
+    ByteBuffer uncompressed_block_data;
-    png_chunk.add_as_big_endian(CMF_FLG);
+    uncompressed_block_data.ensure_capacity(bitmap.size_in_bytes() + bitmap.height());
-
-    NonCompressibleBlock non_compressible_block;
 
     for (int y = 0; y < bitmap.height(); ++y) {
-        non_compressible_block.add_byte_to_block(0, png_chunk);
+        uncompressed_block_data.append(0);
 
         for (int x = 0; x < bitmap.width(); ++x) {
             auto pixel = bitmap.get_pixel(x, y);
-            non_compressible_block.add_byte_to_block(pixel.red(), png_chunk);
+            uncompressed_block_data.append(pixel.red());
-            non_compressible_block.add_byte_to_block(pixel.green(), png_chunk);
+            uncompressed_block_data.append(pixel.green());
-            non_compressible_block.add_byte_to_block(pixel.blue(), png_chunk);
+            uncompressed_block_data.append(pixel.blue());
-            non_compressible_block.add_byte_to_block(pixel.alpha(), png_chunk);
+            uncompressed_block_data.append(pixel.alpha());
         }
     }
-    non_compressible_block.finalize(png_chunk);
 
-    png_chunk.add_as_big_endian(non_compressible_block.adler_s2());
+    auto maybe_zlib_buffer = Compress::ZlibCompressor::compress_all(uncompressed_block_data);
-    png_chunk.add_as_big_endian(non_compressible_block.adler_s1());
+    if (!maybe_zlib_buffer.has_value()) {
+        // FIXME: Handle errors.
+        VERIFY_NOT_REACHED();
+    }
+    auto zlib_buffer = maybe_zlib_buffer.release_value();
 
+    png_chunk.add(zlib_buffer.data(), zlib_buffer.size());
     add_chunk(png_chunk);
 }