546 lines
14 KiB
C++
546 lines
14 KiB
C++
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#include "SMXGif.h"
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#include <stdint.h>
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#include <string>
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#include <vector>
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using namespace std;
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// This is a simple animated GIF decoder. It always decodes to RGBA color,
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// discarding palettes, and decodes the whole file at once.
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class GIFError: public exception { };
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struct Palette
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{
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SMXGif::Color color[256];
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};
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void SMXGif::GIFImage::Init(int width_, int height_)
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{
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width = width_;
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height = height_;
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image.resize(width * height);
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}
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void SMXGif::GIFImage::Clear(const Color &color)
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{
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for(int y = 0; y < height; ++y)
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for(int x = 0; x < width; ++x)
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get(x,y) = color;
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}
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void SMXGif::GIFImage::CropImage(SMXGif::GIFImage &dst, int crop_left, int crop_top, int crop_width, int crop_height) const
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{
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dst.Init(crop_width, crop_height);
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for(int y = 0; y < crop_height; ++y)
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{
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for(int x = 0; x < crop_width; ++x)
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dst.get(x,y) = get(x + crop_left, y + crop_top);
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}
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}
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void SMXGif::GIFImage::Blit(SMXGif::GIFImage &src, int dst_left, int dst_top, int dst_width, int dst_height)
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{
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for(int y = 0; y < dst_height; ++y)
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{
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for(int x = 0; x < dst_width; ++x)
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get(x + dst_left, y + dst_top) = src.get(x, y);
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}
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}
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bool SMXGif::GIFImage::operator==(const GIFImage &rhs) const
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{
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return
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width == rhs.width &&
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height == rhs.height &&
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image == rhs.image;
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}
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class DataStream
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{
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public:
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DataStream(const string &data_):
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data(data_)
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{
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}
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uint8_t ReadByte()
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{
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if(pos >= data.size())
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throw GIFError();
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uint8_t result = data[pos];
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pos++;
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return result;
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}
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uint16_t ReadLE16()
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{
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uint8_t byte1 = ReadByte();
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uint8_t byte2 = ReadByte();
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return byte1 | (byte2 << 8);
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}
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void ReadBytes(string &s, int count)
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{
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s.clear();
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while(count--)
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s.push_back(ReadByte());
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}
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void skip(int bytes)
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{
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pos += bytes;
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}
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private:
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const string &data;
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uint32_t pos = 0;
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};
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class LWZStream
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{
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public:
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LWZStream(DataStream &stream_):
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stream(stream_)
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{
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}
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// Read one LZW code from the input data.
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uint32_t ReadLZWCode(uint32_t bit_count)
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{
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while(bits_in_buffer < bit_count)
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{
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if(bytes_remaining == 0)
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{
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// Read the next block's byte count.
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bytes_remaining = stream.ReadByte();
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if(bytes_remaining == 0)
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throw GIFError();
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}
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// Shift in another 8 bits into the end of self.bits.
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bits |= stream.ReadByte() << bits_in_buffer;
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bits_in_buffer += 8;
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bytes_remaining -= 1;
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}
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// Shift out bit_count worth of data from the end.
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uint32_t result = bits & ((1 << bit_count) - 1);
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bits >>= bit_count;
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bits_in_buffer -= bit_count;
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return result;
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}
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// Skip the rest of the LZW data.
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void Flush()
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{
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stream.skip(bytes_remaining);
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bytes_remaining = 0;
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// If there are any blocks past the end of data, skip them.
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while(1)
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{
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uint8_t blocksize = stream.ReadByte();
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stream.skip(blocksize);
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if(bytes_remaining == 0)
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break;
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}
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}
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private:
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DataStream &stream;
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uint32_t bits = 0;
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int bytes_remaining = 0;
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uint32_t bits_in_buffer = 0;
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};
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struct LWZDecoder
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{
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LWZDecoder(DataStream &stream):
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lzw_stream(LWZStream(stream))
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{
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// Each frame has a single bits field.
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code_bits = stream.ReadByte();
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}
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string DecodeImage();
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private:
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uint16_t code_bits;
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LWZStream lzw_stream;
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};
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static const int GIFBITS = 12;
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string LWZDecoder::DecodeImage()
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{
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uint32_t dictionary_bits = code_bits + 1;
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int prev_code1 = -1;
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int prev_code2 = -1;
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uint32_t clear = 1 << code_bits;
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uint32_t end = clear + 1;
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uint32_t next_free_slot = clear + 2;
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vector<pair<int,int>> dictionary;
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dictionary.resize(1 << GIFBITS);
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// We append to this buffer as we decode data, then append the data in reverse
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// order.
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string append_buffer;
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string result;
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while(1)
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{
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// Flush append_buffer.
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for(int i = append_buffer.size() - 1; i >= 0; --i)
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result.push_back(append_buffer[i]);
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append_buffer.clear();
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uint32_t code1 = lzw_stream.ReadLZWCode(dictionary_bits);
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// printf("%02x");
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if(code1 == end)
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break;
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if(code1 == clear)
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{
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// Clear the dictionary and reset.
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dictionary_bits = code_bits + 1;
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next_free_slot = clear + 2;
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prev_code1 = -1;
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prev_code2 = -1;
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continue;
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}
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uint32_t code2;
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if(code1 < next_free_slot)
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code2 = code1;
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else if(code1 == next_free_slot && prev_code2 != -1)
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{
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append_buffer.push_back(prev_code2);
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code2 = prev_code1;
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}
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else
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throw GIFError();
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// Walk through the linked list of codes in the dictionary and append.
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while(code2 >= clear + 2)
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{
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uint8_t append_char = dictionary[code2].first;
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code2 = dictionary[code2].second;
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append_buffer.push_back(append_char);
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}
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append_buffer.push_back(code2);
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// If we're already at the last free slot, the dictionary is full and can't be expanded.
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if(next_free_slot < static_cast<uint32_t>(1 << dictionary_bits))
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{
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// If we have any free dictionary slots, save.
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if(prev_code1 != -1)
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{
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dictionary[next_free_slot] = make_pair(code2, prev_code1);
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next_free_slot += 1;
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}
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// If we've just filled the last dictionary slot, expand the dictionary size if possible.
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if(next_free_slot >= static_cast<uint32_t>(1 << dictionary_bits) && dictionary_bits < GIFBITS)
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dictionary_bits += 1;
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}
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prev_code1 = code1;
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prev_code2 = code2;
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}
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// Skip any remaining data in this block.
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lzw_stream.Flush();
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return result;
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}
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struct GlobalGIFData
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{
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int width = 0, height = 0;
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int background_index = -1;
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bool use_transparency = false;
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int transparency_index = -1;
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int duration = 0;
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int disposal_method = 0;
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bool have_global_palette = false;
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Palette palette;
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};
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class GIFDecoder
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{
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public:
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GIFDecoder(DataStream &stream_):
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stream(stream_)
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{
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}
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void ReadAllFrames(vector<SMXGif::SMXGifFrame> &frames);
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private:
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bool ReadPacket(string &packet);
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Palette ReadPalette(int palette_size);
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void DecodeImage(GlobalGIFData global_data, SMXGif::GIFImage &out);
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DataStream &stream;
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SMXGif::GIFImage image;
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int frame;
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};
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// Read a palette with size colors.
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//
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// This is a simple string, with 4 RGBA bytes per color.
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Palette GIFDecoder::ReadPalette(int palette_size)
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{
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Palette result;
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for(int i = 0; i < palette_size; ++i)
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{
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result.color[i].color[0] = stream.ReadByte(); // R
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result.color[i].color[1] = stream.ReadByte(); // G
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result.color[i].color[2] = stream.ReadByte(); // B
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result.color[i].color[3] = 0xFF;
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}
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return result;
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}
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bool GIFDecoder::ReadPacket(string &packet)
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{
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uint8_t packet_size = stream.ReadByte();
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if(packet_size == 0)
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return false;
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stream.ReadBytes(packet, packet_size);
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return true;
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}
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void GIFDecoder::ReadAllFrames(vector<SMXGif::SMXGifFrame> &frames)
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{
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string header;
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stream.ReadBytes(header, 6);
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if(header != "GIF87a" && header != "GIF89a")
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throw GIFError();
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GlobalGIFData global_data;
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global_data.width = stream.ReadLE16();
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global_data.height = stream.ReadLE16();
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image.Init(global_data.width, global_data.height);
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// Ignore the aspect ratio field. (Supporting pixel aspect ratios in a format
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// this rudimentary was almost ambitious of them...)
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uint8_t global_flags = stream.ReadByte();
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global_data.background_index = stream.ReadByte();
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// Ignore the aspect ratio field. (Supporting pixel aspect ratios in a format
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// this rudimentary was almost ambitious of them...)
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stream.ReadByte();
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// Decode global_flags.
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uint8_t global_palette_size = global_flags & 0x7;
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global_data.have_global_palette = (global_flags >> 7) & 0x1;
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// If there's no global palette, leave it empty.
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if(global_data.have_global_palette)
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global_data.palette = ReadPalette(1 << (global_palette_size + 1));
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frame = 0;
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// Save a copy of global data, so we can restore it after each frame.
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GlobalGIFData saved_global_data = global_data;
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// Decode all packets.
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while(1)
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{
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uint8_t packet_type = stream.ReadByte();
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if(packet_type == 0x21)
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{
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// Extension packet
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uint8_t extension_type = stream.ReadByte();
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if(extension_type == 0xF9)
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{
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string packet;
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if(!ReadPacket(packet))
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throw GIFError();
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DataStream packet_buf(packet);
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// Graphics control extension
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uint8_t gce_flags = packet_buf.ReadByte();
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global_data.duration = packet_buf.ReadLE16();
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global_data.transparency_index = packet_buf.ReadByte();
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global_data.use_transparency = bool(gce_flags & 1);
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global_data.disposal_method = (gce_flags >> 2) & 0xF;
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if(!global_data.use_transparency)
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global_data.transparency_index = -1;
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}
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// Read any remaining packets in this extension packet.
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while(1)
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{
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string packet;
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if(!ReadPacket(packet))
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break;
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}
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}
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else if(packet_type == 0x2C)
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{
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// Image data
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SMXGif::GIFImage frame_image;
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DecodeImage(global_data, frame_image);
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SMXGif::SMXGifFrame gif_frame;
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gif_frame.width = global_data.width;
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gif_frame.height = global_data.height;
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gif_frame.milliseconds = global_data.duration * 10;
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gif_frame.frame = frame_image;
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// If this frame is identical to the previous one, just extend the previous frame.
|
||
|
|
if(!frames.empty() && gif_frame.frame == frames.back().frame)
|
||
|
|
{
|
||
|
|
frames.back().milliseconds += gif_frame.milliseconds;
|
||
|
|
continue;
|
||
|
|
}
|
||
|
|
|
||
|
|
frames.push_back(gif_frame);
|
||
|
|
|
||
|
|
frame++;
|
||
|
|
|
||
|
|
// Reset GCE (frame-specific) data.
|
||
|
|
global_data = saved_global_data;
|
||
|
|
}
|
||
|
|
else if(packet_type == 0x3B)
|
||
|
|
{
|
||
|
|
// EOF
|
||
|
|
return;
|
||
|
|
}
|
||
|
|
else
|
||
|
|
throw GIFError();
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
// Decode a single GIF image into out, leaving this->image ready for
|
||
|
|
// the next frame (with this frame's dispose applied).
|
||
|
|
void GIFDecoder::DecodeImage(GlobalGIFData global_data, SMXGif::GIFImage &out)
|
||
|
|
{
|
||
|
|
uint16_t block_left = stream.ReadLE16();
|
||
|
|
uint16_t block_top = stream.ReadLE16();
|
||
|
|
uint16_t block_width = stream.ReadLE16();
|
||
|
|
uint16_t block_height = stream.ReadLE16();
|
||
|
|
uint8_t local_flags = stream.ReadByte();
|
||
|
|
|
||
|
|
// area = (block_left, block_top, block_left + block_width, block_top + block_height)
|
||
|
|
// Extract flags:
|
||
|
|
uint8_t have_local_palette = (local_flags >> 7) & 1;
|
||
|
|
// bool interlaced = (local_flags >> 6) & 1;
|
||
|
|
uint8_t local_palette_size = (local_flags >> 0) & 0x7;
|
||
|
|
// print 'Interlaced:', interlaced
|
||
|
|
|
||
|
|
// We don't support interlaced GIFs right now.
|
||
|
|
// assert interlaced == 0
|
||
|
|
|
||
|
|
// If this frame has a local palette, use it. Otherwise, use the global palette.
|
||
|
|
Palette active_palette = global_data.palette;
|
||
|
|
if(have_local_palette)
|
||
|
|
active_palette = ReadPalette(1 << (local_palette_size + 1));
|
||
|
|
|
||
|
|
if(!global_data.have_global_palette && !have_local_palette)
|
||
|
|
{
|
||
|
|
// We have no palette. This is an invalid file.
|
||
|
|
throw GIFError();
|
||
|
|
}
|
||
|
|
|
||
|
|
if(frame == 0)
|
||
|
|
{
|
||
|
|
// On the first frame, clear the buffer. If we have a transparency index,
|
||
|
|
// clear to transparent. Otherwise, clear to the background color.
|
||
|
|
if(global_data.transparency_index != -1)
|
||
|
|
image.Clear(SMXGif::Color(0,0,0,0));
|
||
|
|
else
|
||
|
|
image.Clear(active_palette.color[global_data.background_index]);
|
||
|
|
}
|
||
|
|
|
||
|
|
// Decode the compressed image data.
|
||
|
|
LWZDecoder decoder(stream);
|
||
|
|
string decompressed_data = decoder.DecodeImage();
|
||
|
|
|
||
|
|
if(decompressed_data.size() < block_width*block_height)
|
||
|
|
throw GIFError();
|
||
|
|
|
||
|
|
// Save the region to restore after decoding.
|
||
|
|
SMXGif::GIFImage dispose;
|
||
|
|
if(global_data.disposal_method <= 1)
|
||
|
|
{
|
||
|
|
// No disposal.
|
||
|
|
}
|
||
|
|
else if(global_data.disposal_method == 2)
|
||
|
|
{
|
||
|
|
// Clear the region to a background color afterwards.
|
||
|
|
dispose.Init(block_width, block_height);
|
||
|
|
|
||
|
|
if(global_data.transparency_index != -1)
|
||
|
|
dispose.Clear(SMXGif::Color(0,0,0,0));
|
||
|
|
else
|
||
|
|
{
|
||
|
|
uint8_t palette_idx = global_data.background_index;
|
||
|
|
dispose.Clear(active_palette.color[palette_idx]);
|
||
|
|
}
|
||
|
|
|
||
|
|
}
|
||
|
|
else if(global_data.disposal_method == 3)
|
||
|
|
{
|
||
|
|
// Restore the previous frame afterwards.
|
||
|
|
image.CropImage(dispose, block_left, block_top, block_width, block_height);
|
||
|
|
}
|
||
|
|
else
|
||
|
|
{
|
||
|
|
// Unknown disposal method
|
||
|
|
}
|
||
|
|
|
||
|
|
int pos = 0;
|
||
|
|
for(int y = block_top; y < block_top + block_height; ++y)
|
||
|
|
{
|
||
|
|
for(int x = block_left; x < block_left + block_width; ++x)
|
||
|
|
{
|
||
|
|
uint8_t palette_idx = decompressed_data[pos];
|
||
|
|
pos++;
|
||
|
|
|
||
|
|
if(palette_idx == global_data.transparency_index)
|
||
|
|
{
|
||
|
|
// If this pixel is transparent, leave the existing color in place.
|
||
|
|
}
|
||
|
|
else
|
||
|
|
{
|
||
|
|
image.get(x,y) = active_palette.color[palette_idx];
|
||
|
|
}
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
// Copy the image before we run dispose.
|
||
|
|
out = image;
|
||
|
|
|
||
|
|
// Restore the dispose area.
|
||
|
|
if(dispose.width != 0)
|
||
|
|
image.Blit(dispose, block_left, block_top, block_width, block_height);
|
||
|
|
}
|
||
|
|
|
||
|
|
bool SMXGif::DecodeGIF(string buf, vector<SMXGif::SMXGifFrame> &frames)
|
||
|
|
{
|
||
|
|
DataStream stream(buf);
|
||
|
|
GIFDecoder gif(stream);
|
||
|
|
try {
|
||
|
|
gif.ReadAllFrames(frames);
|
||
|
|
} catch(GIFError &) {
|
||
|
|
// We don't return error strings for this, just success or failure.
|
||
|
|
return false;
|
||
|
|
}
|
||
|
|
return true;
|
||
|
|
}
|