-static void
-pngWriteCallback(png_structp png_ptr, png_bytep data, png_size_t length)
-{
- std::ostream *os = (std::ostream *) png_get_io_ptr(png_ptr);
- os->write((const char *)data, length);
-}
-
-bool
-writePixelsToBuffer(std::ostream &os,
- unsigned char *pixels,
- unsigned width, unsigned height, unsigned numChannels,
- bool flipped)
-{
- png_structp png_ptr;
- png_infop info_ptr;
- int type;
-
- switch (numChannels) {
- case 4:
- type = PNG_COLOR_TYPE_RGB_ALPHA;
- break;
- case 3:
- type = PNG_COLOR_TYPE_RGB;
- break;
- case 2:
- type = PNG_COLOR_TYPE_GRAY_ALPHA;
- break;
- case 1:
- type = PNG_COLOR_TYPE_GRAY;
- break;
- default:
- goto no_png;
- }
-
- png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL, NULL, NULL);
- if (!png_ptr)
- goto no_png;
-
- info_ptr = png_create_info_struct(png_ptr);
- if (!info_ptr) {
- png_destroy_write_struct(&png_ptr, NULL);
- goto no_png;
- }
-
- if (setjmp(png_jmpbuf(png_ptr))) {
- png_destroy_write_struct(&png_ptr, &info_ptr);
- goto no_png;
- }
-
- png_set_write_fn(png_ptr, &os, pngWriteCallback, NULL);
-
- png_set_IHDR(png_ptr, info_ptr, width, height, 8,
- type, PNG_INTERLACE_NONE,
- PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
-
- png_set_compression_level(png_ptr, png_compression_level);
-
- png_write_info(png_ptr, info_ptr);
-
- if (!flipped) {
- for (unsigned y = 0; y < height; ++y) {
- png_bytep row = (png_bytep)(pixels + y*width*numChannels);
- png_write_rows(png_ptr, &row, 1);
- }
- } else {
- unsigned y = height;
- while (y--) {
- png_bytep row = (png_bytep)(pixels + y*width*numChannels);
- png_write_rows(png_ptr, &row, 1);
- }
- }
-
- png_write_end(png_ptr, info_ptr);
- png_destroy_write_struct(&png_ptr, &info_ptr);
-
- return true;
-
-no_png:
- return false;
-}