81 lines
2.7 KiB
C++
81 lines
2.7 KiB
C++
#include <mbgl/util/compression.hpp>
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#include <mbgl/util/image.hpp>
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#include <mbgl/util/premultiply.hpp>
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#pragma GCC diagnostic push
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#pragma GCC diagnostic ignored "-Wshadow"
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#include <boost/crc.hpp>
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#pragma GCC diagnostic pop
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#include <cassert>
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#include <cstring>
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#define NETWORK_BYTE_UINT32(value) \
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char(value >> 24), char(value >> 16), char(value >> 8), char(value >> 0)
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namespace {
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void addChunk(std::string& png, const char* type, const char* data = "", const uint32_t size = 0) {
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assert(strlen(type) == 4);
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// Checksum encompasses type + data
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boost::crc_32_type checksum;
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checksum.process_bytes(type, 4);
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checksum.process_bytes(data, size);
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const char length[4] = { NETWORK_BYTE_UINT32(size) };
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const char crc[4] = { NETWORK_BYTE_UINT32(checksum.checksum()) };
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png.reserve(png.size() + 4 /* length */ + 4 /* type */ + size + 4 /* CRC */);
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png.append(length, 4);
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png.append(type, 4);
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png.append(data, size);
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png.append(crc, 4);
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}
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} // namespace
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namespace mbgl {
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// Encode PNGs without libpng.
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std::string encodePNG(const PremultipliedImage& pre) {
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// Make copy of the image so that we can unpremultiply it.
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const auto src = util::unpremultiply(pre.clone());
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// PNG magic bytes
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const char preamble[8] = { char(0x89), 'P', 'N', 'G', '\r', '\n', 0x1a, '\n' };
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// IHDR chunk for our RGBA image.
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const char ihdr[13] = {
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NETWORK_BYTE_UINT32(src.size.width), // width
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NETWORK_BYTE_UINT32(src.size.height), // height
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8, // bit depth == 8 bits
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6, // color type == RGBA
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0, // compression method == deflate
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0, // filter method == default
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0, // interlace method == none
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};
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// Prepare the (compressed) data chunk.
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const auto stride = src.stride();
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std::string idat;
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for (uint32_t y = 0; y < src.size.height; y++) {
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// Every scanline needs to be prefixed with one byte that indicates the filter type.
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idat.append(1, 0); // filter type 0
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idat.append((const char*)(src.data.get() + y * stride), stride);
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}
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idat = util::compress(idat);
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// Assemble the PNG.
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std::string png;
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png.reserve((8 /* preamble */) + (12 + 13 /* IHDR */) +
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(12 + idat.size() /* IDAT */) + (12 /* IEND */));
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png.append(preamble, 8);
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addChunk(png, "IHDR", ihdr, 13);
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addChunk(png, "IDAT", idat.data(), static_cast<uint32_t>(idat.size()));
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addChunk(png, "IEND");
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return png;
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}
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} // namespace mbgl
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