palladium/pd/image/source/img_blur.cpp

/*
MIT License

Copyright (c) 2024 - 2025 tobid7

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
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The above copyright notice and this permission notice shall be included in all
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IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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 */

#include <cstring>
#include <memory>
#include <pd/image/img_blur.hpp>
#include <pd/image/img_convert.hpp>

namespace PD {
namespace ImgBlur {
PD_IMAGE_API std::vector<float> GaussianKernel(int r, float si) {
  /// Define radius as r to be shorter
  int size = 2 * r + 1;
  std::vector<float> kernel(size);
  float sum = 0.0f;

  for (int i = -r; i <= r; i++) {
    kernel[i + r] = exp(-0.5f * (i * i) / (si * si));
    sum += kernel[i + r];
  }

  for (int i = 0; i < size; i++) {
    kernel[i] /= sum;
  }
  return kernel;
}
PD_IMAGE_API void GaussianBlur(std::vector<u8> &buf, int w, int h, float radius,
                               float si,
                               std::function<int(int, int, int)> idxfn) {
  GaussianBlur(buf.data(), w, h, 4, radius, si, idxfn);
}

PD_IMAGE_API void GaussianBlur(void *buf, int w, int h, int bpp, float radius,
                               float si,
                               std::function<int(int, int, int)> idxfn) {
  if (bpp != 4 && bpp != 3) {
    return;
  }
  std::vector<float> kernel = GaussianKernel(radius, si);
  int hks = kernel.size() / 2;
  int end = w * h * bpp;
  std::vector<unsigned char> res((u8 *)buf, ((u8 *)buf) + end);
  ImgConvert::Reverse32(res, w, h);
  for (int y = 0; y < h; y++) {
    for (int x = 0; x < w; x++) {
      float r = 0.0f, g = 0.0f, b = 0.0f;
      for (int ky = -hks; ky <= hks; ky++) {
        for (int kx = -hks; kx <= hks; kx++) {
          int xoff = std::min(std::max(x + kx, 0), w - 1);
          int yoff = std::min(std::max(y + ky, 0), h - 1);
          int idx = idxfn(xoff, yoff, w) * 4;

          float weight = kernel[ky + hks] * kernel[kx + hks];
          r += ((u8 *)buf)[idx] * weight;
          g += ((u8 *)buf)[idx + 1] * weight;
          b += ((u8 *)buf)[idx + 2] * weight;
        }
      }
      int idx = idxfn(x, y, w) * bpp;
      res[idx] = std::min(std::max(int(r), 0), 255);
      res[idx + 1] = std::min(std::max(int(g), 0), 255);
      res[idx + 2] = std::min(std::max(int(b), 0), 255);
    }
  }
  ImgConvert::Reverse32(res, w, h);
  std::memcpy(buf, res.data(), res.size());
}
}  // namespace ImgBlur
}  // namespace PD