From af6fad72ebfb98e71574bbe8a4b57920902159ca Mon Sep 17 00:00:00 2001
From: James Grogan <grogan.ox@gmail.com>
Date: Tue, 29 Nov 2022 12:05:08 +0000
Subject: [PATCH] Convert lz77 to use fixed buffer sizes.

---
 src/compression/Lz77Encoder.cpp            | 272 +++++++++++++++------
 src/compression/Lz77Encoder.h              |  33 ++-
 src/compression/huffman/HuffmanEncoder.cpp |  44 ++++
 src/compression/huffman/HuffmanEncoder.h   |  42 ++--
 src/image/png/PngWriter.cpp                |  12 +-
 src/image/png/PngWriter.h                  |   2 +-
 test/CMakeLists.txt                        |   1 +
 test/compression/TestLz77Encoder.cpp       |  32 +++
 test/image/TestPngWriter.cpp               |  34 ++-
 9 files changed, 362 insertions(+), 110 deletions(-)
 create mode 100644 test/compression/TestLz77Encoder.cpp

diff --git a/src/compression/Lz77Encoder.cpp b/src/compression/Lz77Encoder.cpp
index cecf977..9818a64 100644
--- a/src/compression/Lz77Encoder.cpp
+++ b/src/compression/Lz77Encoder.cpp
@@ -8,55 +8,102 @@
 #include <iostream>
 
 Lz77Encoder::Lz77Encoder(BitStream* inputStream, BitStream* outputStream)
-    : AbstractEncoder(inputStream, outputStream)
+    : AbstractEncoder(inputStream, outputStream),
+      mSearchBuffer(mSearchBufferSize),
+      mLookaheadBuffer(mLookAheadBufferSize)
 {
 
 }
 
-
-unsigned Lz77Encoder::lookAheadForMatchingChars(std::vector<char>& matchBuffer, unsigned searchIndex, unsigned hitOffset, const std::string& stream, unsigned streamLoc)
+void Lz77Encoder::setPrefixCodeGenerator(std::unique_ptr<PrefixCodeGenerator> generator)
 {
-    auto remaining_size = stream.size() - streamLoc;
+    mCodeGenerator = std::move(generator);
+}
 
-    unsigned num_hits{1};
-    for (unsigned jdx=1; jdx< remaining_size; jdx++)
+bool Lz77Encoder::hitBufferFull() const
+{
+    return mHitBuffer.size() == mMaxHitBufferSize;
+}
+
+void Lz77Encoder::populateSearchBuffer(const Hit& hit)
+{
+    const auto& [length, distance, next_char] = hit;
+
+    if (length == 0)
     {
-        char buffer_char{0};
-        if (searchIndex + jdx < mSearchBuffer.size())
+        mSearchBuffer.addItem(next_char);
+    }
+    else
+    {
+        std::vector<unsigned char> new_items(distance, 0);
+        for(unsigned idx=0 ;idx<distance; idx++)
         {
-            buffer_char = mSearchBuffer[searchIndex + jdx];
+            new_items[idx] = getSearchBufferItem(idx);
         }
-        else
+        for(auto item : new_items)
         {
-            buffer_char = stream[jdx - hitOffset];
+            mSearchBuffer.addItem(item);
         }
 
-        auto lookahead_char = stream[streamLoc + jdx];
-        if (lookahead_char == buffer_char)
+        int difference = int(length) - distance;
+        if (difference > 0)
         {
-            matchBuffer.push_back(buffer_char);
-            num_hits++;
+            for(unsigned idx=0; idx<difference; idx++)
+            {
+                mSearchBuffer.addItem(mLookaheadBuffer.getItem(idx));
+            }
+        }
+    }
+}
+
+unsigned char Lz77Encoder::getSearchBufferItem(unsigned index) const
+{
+    return mSearchBuffer.getItem(mSearchBuffer.getNumItems() - 1 - index);
+}
+
+unsigned Lz77Encoder::lookAheadForMatchingChars(unsigned distance)
+{
+    unsigned length{0};
+    std::cout << "In hit check at distance " << distance << " max buffer index is: " << mMaxLookAheadBufferIndex << std::endl;
+    for(unsigned idx=0; idx<mMaxLookAheadBufferIndex + 1; idx++)
+    {
+        int search_offset = int(distance-1) - idx;
+        std::cout << "Have search offet " << search_offset << std::endl;
+        unsigned char search_char{0};
+        if (search_offset < 0)
+        {
+            search_char = mLookaheadBuffer.getItem(-search_offset - 1);
         }
         else
         {
+            search_char = getSearchBufferItem(static_cast<unsigned>(search_offset));
+        }
+
+        unsigned char lookahead_char = mLookaheadBuffer.getItem(idx);
+
+        std::cout << "Checking search char " << static_cast<int>(search_char) << " and lookup char " << static_cast<int>(lookahead_char) << std::endl;
+        if ((lookahead_char != search_char) || (idx == mMaxLookAheadBufferIndex))
+        {
+            if (idx + 1>= mMinLengthMatchSize)
+            {
+                length = idx + 1;
+            }
             break;
         }
     }
-    return num_hits;
+    return length;
 }
 
-void Lz77Encoder::lookThroughSearchBuffer(char searchChar, unsigned& hitLength, unsigned& hitOffset, const std::string& stream, unsigned streamLoc)
+void Lz77Encoder::lookForMatches(unsigned char searchChar, unsigned& hitLength, unsigned& hitOffset)
 {
-    for(unsigned idx=0; idx<mSearchBuffer.size(); idx++)
+    for (unsigned idx = 0; idx< mSearchBuffer.getNumItems(); idx++)
     {
-        auto search_index = mSearchBuffer.size() - idx - 1;
-
-        if (auto buffer_char = mSearchBuffer[search_index]; buffer_char == searchChar)
+        if (mSearchBuffer.getItem(mSearchBuffer.getNumItems() - 1 - idx) == searchChar)
         {
-            std::vector<char> match_buffer{buffer_char};
-            auto num_hits = lookAheadForMatchingChars(match_buffer, search_index, idx, stream, streamLoc);
+            std::cout << "Looking for hits " << std::endl;
+            auto num_hits = lookAheadForMatchingChars(idx + 1);
 
-            if (num_hits >= hitLength)
+            if (num_hits > 0 && num_hits >= hitLength)
             {
                 hitLength = num_hits;
                 hitOffset = idx + 1;
@@ -65,75 +112,163 @@ void Lz77Encoder::lookThroughSearchBuffer(char searchChar, unsigned& hitLength,
     }
 }
 
-void Lz77Encoder::setPrefixCodeGenerator(std::unique_ptr<PrefixCodeGenerator> generator)
+bool Lz77Encoder::lookAheadSourceEmpty() const
 {
-    mCodeGenerator = std::move(generator);
+    if (mLookaheadBuffer.getNumItems() < mLookAheadBufferSize)
+    {
+        return true;
+    }
+
+    if (mMaxLookAheadBufferIndex < mLookAheadBufferSize - 1)
+    {
+        return true;
+    }
+
+    return false;
+}
+
+void Lz77Encoder::populateLookaheadBuffer(unsigned size, bool firstPass)
+{
+    if (!firstPass && lookAheadSourceEmpty())
+    {
+        for(unsigned idx=0; idx<size; idx++)
+        {
+            mLookaheadBuffer.addItem(0);
+            mMaxLookAheadBufferIndex--;
+        }
+        return;
+    }
+
+    bool stream_finished{false};
+    unsigned stream_end_id{0};
+    for(unsigned idx=0; idx<size; idx++)
+    {
+        if (!stream_finished)
+        {
+            auto byte = mInputStream->readNextByte();
+            if (!byte)
+            {
+                stream_finished = true;
+                stream_end_id = idx -1;
+                mLookaheadBuffer.addItem(0);
+                mMaxLookAheadBufferIndex--;
+                continue;
+            }
+            else
+            {
+                mLookaheadBuffer.addItem(*byte);
+            }
+        }
+        else
+        {
+            mLookaheadBuffer.addItem(0);
+            mMaxLookAheadBufferIndex--;
+        }
+    }
+
+    if (stream_finished && firstPass)
+    {
+        mMaxLookAheadBufferIndex = stream_end_id;
+    }
 }
 
 bool Lz77Encoder::encode()
 {
     if (!mCodeGenerator)
     {
-        auto code_generator = std::make_unique<HuffmanEncoder>();
-        auto huffman_encoder = code_generator.get();
-
-        mCodeGenerator = std::move(code_generator);
-        huffman_encoder->setUseFixedCode(true);
-        huffman_encoder->initializeLiteralLengthTable();
+        mCodeGenerator = std::make_unique<HuffmanEncoder>();
     }
 
-    while(auto byte = mInputStream->readNextByte())
+    // Fill the lookahead buffer
+    mMaxLookAheadBufferIndex = mLookAheadBufferSize - 1;
+    populateLookaheadBuffer(mLookAheadBufferSize, true);
+    if(mMaxLookAheadBufferIndex < 0)
     {
-        const auto code = mCodeGenerator->getLiteralValue(*byte);
-
-        std::cout << "Writing value " << static_cast<int>(*byte) << " with code " << ByteUtils::toString(code.getData(), code.getLength()) << "\n";
-
-        mOutputStream->writeNBits(code.getData(), code.getLength());
+        return true;
     }
 
-    auto eos_code = mCodeGenerator->getEndOfStreamValue();
-    std::cout << "Writing EOS value with code " << ByteUtils::toString(eos_code.getData(), eos_code.getLength()) << "\n";
-
-    mOutputStream->writeNBits(eos_code.getData(), eos_code.getLength());
-
-
-
-    /*
-    unsigned loc{0};
-    std::string ret;
-
-    while(!mInputStream->isFinished())
+    bool input_stream_ended{false};
+    while(!hitBufferFull())
     {
-        auto search_char = stream[loc];
+        if (mMaxLookAheadBufferIndex < 0)
+        {
+            input_stream_ended = true;
+            break;
+        }
+
+        const auto working_byte = mLookaheadBuffer.getItem(0);
+        std::cout << "Working byte is " << static_cast<int>(working_byte) << std::endl;
 
         unsigned hit_length{0};
-        unsigned hit_offset{0};
-        lookThroughSearchBuffer(search_char, hit_length, hit_offset, stream, loc);
+        unsigned hit_distance{0};
+        lookForMatches(working_byte, hit_length, hit_distance);
 
-        if (hit_length > 0)
+        std::cout << "Got hit length " << hit_length << " and distance " << hit_distance << std::endl;
+
+        const Hit hit{hit_length, hit_distance, working_byte};
+        mHitBuffer.push_back(hit);
+
+        populateSearchBuffer(hit);
+        if (hit_length == 0)
         {
-            ret += "@" + std::to_string(hit_offset) + "L" + std::to_string(hit_length);
-            loc+=hit_length;
-
-            auto hit_loc = mSearchBuffer.size() - hit_offset;
-            for(unsigned idx=hit_loc; idx<hit_loc + hit_length; idx++)
-            {
-                mSearchBuffer.push_back(mSearchBuffer[idx]);
-            }
+            populateLookaheadBuffer(1);
         }
         else
         {
-            ret += search_char;
-            mSearchBuffer.push_back(search_char);
-            loc++;
+            populateLookaheadBuffer(hit_length);
         }
     }
 
-    return ret;
-    */
-    return false;
+    return input_stream_ended;
 }
 
+const std::vector<Lz77Encoder::Hit>& Lz77Encoder::getHitBuffer() const
+{
+    return mHitBuffer;
+}
+
+/*
+void Lz77Encoder::flushHitBuffer()
+{
+    // If dynamic huffman build trees
+    if (!mCodeGenerator)
+    {
+        mCodeGenerator = std::make_unique<HuffmanEncoder>();
+    }
+
+    // Convert hit buffer to prefix codes and write to output stream
+    for (const auto& hit : mHitBuffer)
+    {
+        const auto& [length, distance, next_char] = hit;
+
+        PrefixCode code;
+        if (length == 0)
+        {
+            code = *mCodeGenerator->getLiteralValue(next_char);
+            std::cout << "Writing symbol " << static_cast<int>(next_char) << " with code " << ByteUtils::toString(code.getData(), code.getLength()) << "\n";
+
+            mOutputStream->writeNBits(code.getData(), code.getLength());
+        }
+        else
+        {
+            code = *mCodeGenerator->getLengthValue(length);
+            const auto distance_code = mCodeGenerator->getDistanceValue(distance);
+
+            std::cout << "Writing length " << length << " with code " << ByteUtils::toString(code.getData(), code.getLength()) << "\n";
+            mOutputStream->writeNBits(code.getData(), code.getLength());
+
+            std::cout << "Writing distance " << distance << " with code " << ByteUtils::toString(distance_code.getData(), distance_code.getLength()) << "\n";
+            mOutputStream->writeNBits(distance_code.getData(), distance_code.getLength());
+        }
+    }
+
+    auto eos_code = mCodeGenerator->getEndOfStreamValue();
+    std::cout << "Writing EOS value with code " << ByteUtils::toString(eos_code->getData(), eos_code->getLength()) << "\n";
+
+    mOutputStream->writeNBits(eos_code->getData(), eos_code->getLength());
+}
+*/
+
 bool Lz77Encoder::decode()
 {
     /*
@@ -203,3 +338,4 @@ bool Lz77Encoder::decode()
     */
     return false;
 }
+
diff --git a/src/compression/Lz77Encoder.h b/src/compression/Lz77Encoder.h
index ae5a80f..0d3ec85 100644
--- a/src/compression/Lz77Encoder.h
+++ b/src/compression/Lz77Encoder.h
@@ -2,40 +2,59 @@
 
 #include "AbstractEncoder.h"
 #include "HuffmanEncoder.h"
+#include "CircleBuffer.h"
 
 #include <string>
 #include <vector>
 #include <memory>
+#include <tuple>
 
 class PrefixCodeGenerator;
 
 class Lz77Encoder : public AbstractEncoder
 {
 public:
-    using Buffer = std::vector<unsigned char>;
+    using Hit = std::tuple<unsigned, unsigned, unsigned char>;
 
     Lz77Encoder(BitStream* inputStream, BitStream* outputStream);
 
-    unsigned lookAheadForMatchingChars(std::vector<char>& matchBuffer, unsigned searchIndex, unsigned hitOffset, const std::string& stream, unsigned streamLoc);
-
-    void lookThroughSearchBuffer(char searchChar, unsigned& hitLength, unsigned& hitOffset, const std::string& stream, unsigned streamLoc);
-
     bool encode() override;
 
     bool decode() override;
 
+    const std::vector<Hit>& getHitBuffer() const;
+
     void setSearchBufferSize(unsigned size);
 
     void setLookAheadBufferSize(unsigned size);
 
     void setPrefixCodeGenerator(std::unique_ptr<PrefixCodeGenerator> generator);
 
+    bool hitBufferFull() const;
+
 private:
+
+    bool lookAheadSourceEmpty() const;
+    unsigned char getSearchBufferItem(unsigned index) const;
+
+    unsigned lookAheadForMatchingChars(unsigned searchIndex);
+
+    void lookForMatches(unsigned char searchChar, unsigned& hitLength, unsigned& hitOffset);
+
+    void populateLookaheadBuffer(unsigned size, bool firstPass = false);
+
+    void populateSearchBuffer(const Hit& hit);
+
+    unsigned mMaxHitBufferSize{32000};
+    std::vector<Hit> mHitBuffer;
+
     unsigned mSearchBufferSize{32000};
-    Buffer mSearchBuffer;
+    CircleBuffer<unsigned char> mSearchBuffer;
 
     unsigned mLookAheadBufferSize{256};
-    Buffer mLookaheadBuffer;
+    int mMaxLookAheadBufferIndex{0};
+    unsigned mMinLengthMatchSize{1};
 
+    CircleBuffer<unsigned char>  mLookaheadBuffer;
     std::unique_ptr<PrefixCodeGenerator> mCodeGenerator;
 };
diff --git a/src/compression/huffman/HuffmanEncoder.cpp b/src/compression/huffman/HuffmanEncoder.cpp
index 852f8d7..35d56f5 100644
--- a/src/compression/huffman/HuffmanEncoder.cpp
+++ b/src/compression/huffman/HuffmanEncoder.cpp
@@ -98,3 +98,47 @@ void HuffmanEncoder::encode(const std::unordered_map<unsigned char, unsigned>& c
 
     std::cout << "********" << std::endl;
 }
+
+void HuffmanEncoder::setUseFixedCode(bool useFixed)
+{
+    mUseFixedCode = useFixed;
+}
+
+uint32_t HuffmanEncoder::getLengthValue(unsigned length)
+{
+    return 0;
+}
+
+std::optional<PrefixCode> HuffmanEncoder::getLiteralValue(unsigned char value) const
+{
+    return mLiteralLengthTable.getCodeForSymbol(value);
+}
+
+std::optional<PrefixCode> HuffmanEncoder::getLengthValue(unsigned length) const
+{
+    return mLiteralLengthTable.getCodeForSymbol(length);
+}
+
+std::optional<PrefixCode> HuffmanEncoder::getDistanceValue(unsigned distance) const
+{
+    return mDistanceTable.getCodeForSymbol(distance);
+}
+
+std::optional<PrefixCode> HuffmanEncoder::getEndOfStreamValue() const
+{
+    return mLiteralLengthTable.getCodeForSymbol(256);
+}
+
+void HuffmanEncoder::initializeTrees()
+{
+    initializeLiteralLengthTable();
+}
+
+void HuffmanEncoder::initializeLiteralLengthTable()
+{
+    if(mUseFixedCode)
+    {
+        mLiteralLengthTable.setInputLengthSequence(HuffmanFixedCodes::getDeflateFixedHuffmanCodes(), false);
+        mLiteralLengthTable.buildPrefixCodes();
+    }
+}
diff --git a/src/compression/huffman/HuffmanEncoder.h b/src/compression/huffman/HuffmanEncoder.h
index c092ac9..87285d4 100644
--- a/src/compression/huffman/HuffmanEncoder.h
+++ b/src/compression/huffman/HuffmanEncoder.h
@@ -12,10 +12,11 @@ class PrefixCodeGenerator
 {
 public:
     virtual ~PrefixCodeGenerator() = default;
-    virtual const PrefixCode& getLiteralValue(unsigned char value) const = 0;
-
-    virtual const PrefixCode& getEndOfStreamValue() const = 0;
+    virtual std::optional<PrefixCode> getLiteralValue(unsigned char symbol) const = 0;
+    virtual std::optional<PrefixCode> getLengthValue(unsigned length) const = 0;
+    virtual std::optional<PrefixCode> getDistanceValue(unsigned distance) const = 0;
 
+    virtual std::optional<PrefixCode> getEndOfStreamValue() const = 0;
 };
 
 class HuffmanEncoder : public PrefixCodeGenerator
@@ -27,36 +28,23 @@ public:
     void encode(const DataStream& stream);
     void encode(const std::unordered_map<unsigned char, unsigned>& counts);
 
-    void setUseFixedCode(bool useFixed)
-    {
-        mUseFixedCode = useFixed;
-    }
+    uint32_t getLengthValue(unsigned length);
 
-    uint32_t getLengthValue(unsigned length)
-    {
-        return 0;
-    }
+    std::optional<PrefixCode> getLiteralValue(unsigned char symbol) const override;
 
-    const PrefixCode& getLiteralValue(unsigned char value) const override
-    {
-        return mLiteralLengthTable.getCode(value);
-    }
+    std::optional<PrefixCode> getLengthValue(unsigned length) const override;
 
-    const PrefixCode& getEndOfStreamValue() const override
-    {
-        return mLiteralLengthTable.getCode(256);
-    }
+    std::optional<PrefixCode> getDistanceValue(unsigned distance) const override;
 
-    void initializeLiteralLengthTable()
-    {
-        if(mUseFixedCode)
-        {
-            mLiteralLengthTable.setInputLengthSequence(HuffmanFixedCodes::getDeflateFixedHuffmanCodes(), false);
-            mLiteralLengthTable.buildPrefixCodes();
-        }
-    }
+    std::optional<PrefixCode> getEndOfStreamValue() const override;
+
+    void initializeTrees();
+
+    void setUseFixedCode(bool useFixed);
 
 private:
+    void initializeLiteralLengthTable();
+
     void dumpTree(const RawTree<CountPair>& tree) const;
     void dumpNode(RawNode<CountPair>* node, unsigned depth) const;
 
diff --git a/src/image/png/PngWriter.cpp b/src/image/png/PngWriter.cpp
index ac7ff95..168eb85 100644
--- a/src/image/png/PngWriter.cpp
+++ b/src/image/png/PngWriter.cpp
@@ -9,6 +9,7 @@
 #include "PngFilter.h"
 #include "Lz77Encoder.h"
 #include "ZlibEncoder.h"
+#include "HuffmanEncoder.h"
 #include "CyclicRedundancyChecker.h"
 
 #include "ByteUtils.h"
@@ -181,10 +182,6 @@ void PngWriter::write(const std::unique_ptr<Image<unsigned char> >& image)
     auto filter_out_stream = std::make_unique<BufferBitStream>();
     PngFilter filter(raw_image_stream, filter_out_stream.get());
     filter.encode();
-    //while(!filter_out_stream->isFinished())
-    //{
-        //std::cout << "Got pix " << static_cast<int>(*filter_out_stream->readNextByte()) << std::endl;
-    //}
 
     filter_out_stream->resetOffsets();
 
@@ -199,9 +196,12 @@ void PngWriter::write(const std::unique_ptr<Image<unsigned char> >& image)
         lz77_out_stream = std::make_unique<BufferBitStream>();
         Lz77Encoder lz77_encoder(filter_out_stream.get(), lz77_out_stream.get());
 
-        if (mCompressionMethod == Deflate::CompressionMethod::DYNAMIC_HUFFMAN)
+        if (mCompressionMethod == Deflate::CompressionMethod::FIXED_HUFFMAN)
         {
-            // Set up custom encoder;
+            auto huffman_encoder = std::make_unique<HuffmanEncoder>();
+            huffman_encoder->setUseFixedCode(true);
+            huffman_encoder->initializeTrees();
+            lz77_encoder.setPrefixCodeGenerator(std::move(huffman_encoder));
         }
         lz77_encoder.encode();
         lz77_out_stream->resetOffsets();
diff --git a/src/image/png/PngWriter.h b/src/image/png/PngWriter.h
index 7e8ae6a..c153b24 100644
--- a/src/image/png/PngWriter.h
+++ b/src/image/png/PngWriter.h
@@ -50,7 +50,7 @@ private:
     PngInfo mPngInfo;
     PngHeader mPngHeader;
 
-    Deflate::CompressionMethod mCompressionMethod{Deflate::CompressionMethod::NONE};
+    Deflate::CompressionMethod mCompressionMethod{Deflate::CompressionMethod::DYNAMIC_HUFFMAN};
 };
 
 using PngWriterPtr = std::unique_ptr<PngWriter>;
diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt
index eca43e6..3fc9442 100644
--- a/test/CMakeLists.txt
+++ b/test/CMakeLists.txt
@@ -19,6 +19,7 @@ list(APPEND TestFiles
             compiler/TestTemplatingEngine.cpp
             compression/TestStreamCompressor.cpp
             compression/TestHuffmanStream.cpp
+            compression/TestLz77Encoder.cpp
             database/TestDatabase.cpp
             fonts/TestFontReader.cpp
             graphics/TestRasterizer.cpp
diff --git a/test/compression/TestLz77Encoder.cpp b/test/compression/TestLz77Encoder.cpp
new file mode 100644
index 0000000..87b87f8
--- /dev/null
+++ b/test/compression/TestLz77Encoder.cpp
@@ -0,0 +1,32 @@
+#include <iostream>
+
+#include "Lz77Encoder.h"
+#include "BufferBitStream.h"
+
+int main()
+{
+    std::vector<unsigned> values {0, 10, 11, 12, 10, 11, 12, 0, 13, 14, 15, 10, 11, 12};
+
+    //std::vector<unsigned> values {0, 1, 2, 3, 0, 1, 2, 3, 0,1};
+
+    BufferBitStream input_stream;
+    for (auto value : values)
+    {
+        input_stream.writeByte(value);
+    }
+
+    BufferBitStream output_stream;
+
+    Lz77Encoder encoder(&input_stream, &output_stream);
+
+    encoder.encode();
+
+    auto hit_buffer = encoder.getHitBuffer();
+    for(const auto& hit : hit_buffer)
+    {
+        const auto& [length, distance, next_char] = hit;
+        std::cout << "Got hit " << length << " | " << distance << " | " << static_cast<int>(next_char) << std::endl;
+    }
+
+    return 0;
+}
diff --git a/test/image/TestPngWriter.cpp b/test/image/TestPngWriter.cpp
index 297c9cf..04e04ab 100644
--- a/test/image/TestPngWriter.cpp
+++ b/test/image/TestPngWriter.cpp
@@ -28,6 +28,7 @@ void testCompressedPng()
 
     PngWriter writer;
     writer.setPath("test_compressed.png");
+    writer.setCompressionMethod(Deflate::CompressionMethod::NONE);
     writer.write(image);
 
     return;
@@ -72,9 +73,40 @@ void testFixedPng()
 
 }
 
+void testDynamicCompressedPng()
+{
+    unsigned width = 10;
+    unsigned height = 10;
+    unsigned numChannels = 1;
+    auto image = Image<unsigned char>::Create(width, height);
+    image->setNumChannels(numChannels);
+    image->setBitDepth(8);
+
+    std::vector<unsigned char> data(width*height, 0);
+    for (unsigned idx=0; idx<width*height; idx++)
+    {
+        //unsigned char val = 100 * idx /(width*height);
+        unsigned char val = 10;
+        data[idx] = val;
+    }
+
+    image->setData(data);
+
+    PngWriter writer;
+    writer.setPath("test_dynamic.png");
+    writer.write(image);
+
+    //return;
+    File test_file("test_dynamic.png");
+    std::cout << test_file.dumpBinary();
+
+}
+
 int main()
 {
     //testCompressedPng();
-    testFixedPng();
+    //testFixedPng();
+    testDynamicCompressedPng();
+
     return 0;
 }