+struct VectorDestinationManager {
+ jpeg_destination_mgr pub;
+ std::vector<uint8_t> dest;
+
+ VectorDestinationManager()
+ {
+ pub.init_destination = init_destination_thunk;
+ pub.empty_output_buffer = empty_output_buffer_thunk;
+ pub.term_destination = term_destination_thunk;
+ }
+
+ static void init_destination_thunk(j_compress_ptr ptr)
+ {
+ ((VectorDestinationManager *)(ptr->dest))->init_destination();
+ }
+
+ inline void init_destination()
+ {
+ make_room(0);
+ }
+
+ static boolean empty_output_buffer_thunk(j_compress_ptr ptr)
+ {
+ return ((VectorDestinationManager *)(ptr->dest))->empty_output_buffer();
+ }
+
+ inline bool empty_output_buffer()
+ {
+ make_room(dest.size()); // Should ignore pub.free_in_buffer!
+ return true;
+ }
+
+ inline void make_room(size_t bytes_used)
+ {
+ dest.resize(bytes_used + 4096);
+ dest.resize(dest.capacity());
+ pub.next_output_byte = dest.data() + bytes_used;
+ pub.free_in_buffer = dest.size() - bytes_used;
+ }
+
+ static void term_destination_thunk(j_compress_ptr ptr)
+ {
+ ((VectorDestinationManager *)(ptr->dest))->term_destination();
+ }
+
+ inline void term_destination()
+ {
+ dest.resize(dest.size() - pub.free_in_buffer);
+ }
+};
+static_assert(std::is_standard_layout<VectorDestinationManager>::value, "");
+
+vector<uint8_t> encode_jpeg(const uint8_t *y_data, const uint8_t *cb_data, const uint8_t *cr_data, unsigned width, unsigned height)
+{
+ VectorDestinationManager dest;
+
+ jpeg_compress_struct cinfo;
+ jpeg_error_mgr jerr;
+ cinfo.err = jpeg_std_error(&jerr);
+ jpeg_create_compress(&cinfo);
+
+ cinfo.dest = (jpeg_destination_mgr *)&dest;
+ cinfo.input_components = 3;
+ cinfo.in_color_space = JCS_RGB;
+ jpeg_set_defaults(&cinfo);
+ constexpr int quality = 90;
+ jpeg_set_quality(&cinfo, quality, /*force_baseline=*/false);
+
+ cinfo.image_width = width;
+ cinfo.image_height = height;
+ cinfo.raw_data_in = true;
+ jpeg_set_colorspace(&cinfo, JCS_YCbCr);
+ cinfo.comp_info[0].h_samp_factor = 2;
+ cinfo.comp_info[0].v_samp_factor = 1;
+ cinfo.comp_info[1].h_samp_factor = 1;
+ cinfo.comp_info[1].v_samp_factor = 1;
+ cinfo.comp_info[2].h_samp_factor = 1;
+ cinfo.comp_info[2].v_samp_factor = 1;
+ cinfo.CCIR601_sampling = true; // Seems to be mostly ignored by libjpeg, though.
+ jpeg_start_compress(&cinfo, true);
+
+ JSAMPROW yptr[8], cbptr[8], crptr[8];
+ JSAMPARRAY data[3] = { yptr, cbptr, crptr };
+ for (unsigned y = 0; y < height; y += 8) {
+ for (unsigned yy = 0; yy < 8; ++yy) {
+ yptr[yy] = const_cast<JSAMPROW>(&y_data[(height - y - yy - 1) * width]);
+ cbptr[yy] = const_cast<JSAMPROW>(&cb_data[(height - y - yy - 1) * width/2]);
+ crptr[yy] = const_cast<JSAMPROW>(&cr_data[(height - y - yy - 1) * width/2]);
+ }
+
+ jpeg_write_raw_data(&cinfo, data, /*num_lines=*/8);
+ }
+
+ jpeg_finish_compress(&cinfo);
+ jpeg_destroy_compress(&cinfo);
+
+ return move(dest.dest);
+}
+