PNG(8-bit RGBA) texture file masking tool for VRoid Studio

png-masker.cpp

#include <iostream>
#include <png++/png.hpp>
 
int main(int argc, char *argv[])
{
  if (argc != 4) {
    std::cerr << "usage: " << argv[0] << " [source.png] [mask.png] [dest.png]\n";
    return 1;
  }
  try {
    png::image <png::rgba_pixel> image(argv[1]), msk(argv[2]);
    if (image.get_width() != msk.get_width() || image.get_height() != msk.get_height()) {
      std::cerr << "both pixels size are mismatched\n";
      return 1;
    }
    // copy alpha
    for (size_t x = 0; x < image.get_width(); ++x) {
      for (size_t y = 0; y < image.get_height(); ++y) {
        image[y][x].alpha = image[y][x].alpha * (msk[y][x].alpha + 1) / 256;
      }
    }
    image.write(argv[3]);
  } catch (png::error& error) {
    std::cerr << error.what() << "\n";
    return 1;
  }
  return 0;
}