void jpeg_reader<T>::init()
{
jpeg_decompress_struct cinfo;
jpeg_info_guard iguard(&cinfo);
jpeg_error_mgr jerr;
cinfo.err = jpeg_std_error(&jerr);
jerr.error_exit = on_error;
jerr.output_message = on_error_message;
jpeg_create_decompress(&cinfo);
attach_stream(&cinfo, &stream_);
int ret = jpeg_read_header(&cinfo, TRUE);
if (ret != JPEG_HEADER_OK)
throw image_reader_exception("JPEG Reader: failed to read header");
jpeg_start_decompress(&cinfo);
width_ = cinfo.output_width;
height_ = cinfo.output_height;
if (cinfo.out_color_space == JCS_UNKNOWN)
{
throw image_reader_exception("JPEG Reader: failed to read unknown color space");
}
if (cinfo.output_width == 0 || cinfo.output_height == 0)
{
throw image_reader_exception("JPEG Reader: failed to read image size of");
}
}
PremultipliedImage decodeJPEG(const uint8_t* data, size_t size) {
util::CharArrayBuffer dataBuffer { reinterpret_cast<const char*>(data), size };
std::istream stream(&dataBuffer);
jpeg_decompress_struct cinfo;
jpeg_info_guard iguard(&cinfo);
jpeg_error_mgr jerr;
cinfo.err = jpeg_std_error(&jerr);
jerr.error_exit = on_error;
jerr.output_message = on_error_message;
jpeg_create_decompress(&cinfo);
attach_stream(&cinfo, &stream);
int ret = jpeg_read_header(&cinfo, TRUE);
if (ret != JPEG_HEADER_OK)
throw std::runtime_error("JPEG Reader: failed to read header");
jpeg_start_decompress(&cinfo);
if (cinfo.out_color_space == JCS_UNKNOWN)
throw std::runtime_error("JPEG Reader: failed to read unknown color space");
if (cinfo.output_width == 0 || cinfo.output_height == 0)
throw std::runtime_error("JPEG Reader: failed to read image size");
size_t width = cinfo.output_width;
size_t height = cinfo.output_height;
size_t components = cinfo.output_components;
size_t rowStride = components * width;
PremultipliedImage image({ static_cast<uint32_t>(width), static_cast<uint32_t>(height) });
uint8_t* dst = image.data.get();
JSAMPARRAY buffer = (*cinfo.mem->alloc_sarray)((j_common_ptr) &cinfo, JPOOL_IMAGE, rowStride, 1);
while (cinfo.output_scanline < cinfo.output_height) {
jpeg_read_scanlines(&cinfo, buffer, 1);
for (size_t i = 0; i < width; ++i) {
dst[0] = buffer[0][components * i];
dst[3] = 0xFF;
if (components > 2) {
dst[1] = buffer[0][components * i + 1];
dst[2] = buffer[0][components * i + 2];
} else {
dst[1] = dst[0];
dst[2] = dst[0];
}
dst += 4;
}
}
jpeg_finish_decompress(&cinfo);
return image;
}
void jpeg_reader<T>::read(unsigned x0, unsigned y0, image_data_32& image)
{
stream_.clear();
stream_.seekg(0, std::ios_base::beg);
jpeg_decompress_struct cinfo;
jpeg_info_guard iguard(&cinfo);
jpeg_error_mgr jerr;
cinfo.err = jpeg_std_error(&jerr);
jerr.error_exit = on_error;
jerr.output_message = on_error_message;
jpeg_create_decompress(&cinfo);
attach_stream(&cinfo, &stream_);
int ret = jpeg_read_header(&cinfo, TRUE);
if (ret != JPEG_HEADER_OK) throw image_reader_exception("JPEG Reader read(): failed to read header");
jpeg_start_decompress(&cinfo);
JSAMPARRAY buffer;
int row_stride;
unsigned char a,r,g,b;
row_stride = cinfo.output_width * cinfo.output_components;
buffer = (*cinfo.mem->alloc_sarray) ((j_common_ptr) &cinfo, JPOOL_IMAGE, row_stride, 1);
unsigned w = std::min(unsigned(image.width()),width_ - x0);
unsigned h = std::min(unsigned(image.height()),height_ - y0);
const std::unique_ptr<unsigned int[]> out_row(new unsigned int[w]);
unsigned row = 0;
while (cinfo.output_scanline < cinfo.output_height)
{
jpeg_read_scanlines(&cinfo, buffer, 1);
if (row >= y0 && row < y0 + h)
{
for (unsigned int x = 0; x < w; ++x)
{
unsigned col = x + x0;
a = 255; // alpha not supported in jpg
r = buffer[0][cinfo.output_components * col];
if (cinfo.output_components > 2)
{
g = buffer[0][cinfo.output_components * col + 1];
b = buffer[0][cinfo.output_components * col + 2];
} else {
g = r;
b = r;
}
out_row[x] = color(r, g, b, a).rgba();
}
image.setRow(row - y0, out_row.get(), w);
}
++row;
}
jpeg_finish_decompress(&cinfo);
}
