Function JPEGFileLoader

common/Image.cpp:485–545

}

bool JPEGFileLoader(RGBA8Image* image, const char* filename, std::FILE* fp)
{
	static constexpr u32 BUFFER_SIZE = 16384;

	struct FileCallback
	{
		// Must be the first member (&this == &mgr)
		// We pass a pointer of mgr to libjpeg, and we need to be able to cast it back to FileCallback.
		jpeg_source_mgr mgr;

		std::FILE* fp;
		std::unique_ptr<u8[]> buffer;
		bool end_of_file;
	};

	FileCallback cb = {
		.mgr = {
			.init_source = [](j_decompress_ptr cinfo) {},
			.fill_input_buffer = [](j_decompress_ptr cinfo) -> boolean {
				FileCallback* cb = reinterpret_cast<FileCallback*>(cinfo->src);
				cb->mgr.next_input_byte = cb->buffer.get();
				if (cb->end_of_file)
				{
					cb->buffer[0] = 0xFF;
					cb->buffer[1] = JPEG_EOI;
					cb->mgr.bytes_in_buffer = 2;
					return TRUE;
				}

				const size_t r = std::fread(cb->buffer.get(), 1, BUFFER_SIZE, cb->fp);
				cb->end_of_file |= (std::feof(cb->fp) != 0);
				cb->mgr.bytes_in_buffer = r;
				return TRUE;
			},
			.skip_input_data =
				[](j_decompress_ptr cinfo, long num_bytes) {
					FileCallback* cb = reinterpret_cast<FileCallback*>(cinfo->src);
					const size_t skip_in_buffer = std::min<size_t>(cb->mgr.bytes_in_buffer, static_cast<size_t>(num_bytes));
					cb->mgr.next_input_byte += skip_in_buffer;
					cb->mgr.bytes_in_buffer -= skip_in_buffer;

					const size_t seek_cur = static_cast<size_t>(num_bytes) - skip_in_buffer;
					if (seek_cur > 0)
					{
						if (FileSystem::FSeek64(cb->fp, static_cast<size_t>(seek_cur), SEEK_CUR) != 0)
						{
							cb->end_of_file = true;
							return;
						}
					}
				},
			.resync_to_restart = jpeg_resync_to_restart,
			.term_source = [](j_decompress_ptr cinfo) {},
		},
		.fp = fp,
		.buffer = std::make_unique<u8[]>(BUFFER_SIZE),
		.end_of_file = false,
	};