findTrim function

List<int> findTrim(Image src, { TrimMode mode = TrimMode.transparent, Trim sides = Trim.all, })

Find the crop area to be used by the trim function. Returns the coordinates as x, y, width, height. You could pass these coordinates to the copyCrop function to crop the image.

Implementation

List<int> findTrim(Image src,
    {TrimMode mode = TrimMode.transparent, Trim sides = Trim.all}) {
  var h = src.height;
  var w = src.width;

  final bg = (mode == TrimMode.topLeftColor)
      ? src.getPixel(0, 0)
      : (mode == TrimMode.bottomRightColor)
          ? src.getPixel(w - 1, h - 1)
          : 0;

  var xmin = w;
  var xmax = 0;
  int? ymin;
  var ymax = 0;

  for (var y = 0; y < h; ++y) {
    var first = true;
    for (var x = 0; x < w; ++x) {
      final c = src.getPixel(x, y);
      if ((mode == TrimMode.transparent && getAlpha(c) != 0) ||
          (mode != TrimMode.transparent && (c != bg))) {
        if (xmin > x) {
          xmin = x;
        }
        if (xmax < x) {
          xmax = x;
        }
        ymin ??= y;

        ymax = y;

        if (first) {
          x = xmax;
          first = false;
        }
      }
    }
  }

  // A trim wasn't found
  if (ymin == null) {
    return [0, 0, w, h];
  }

  if (sides & Trim.top == false) {
    ymin = 0;
  }
  if (sides & Trim.bottom == false) {
    ymax = h - 1;
  }
  if (sides & Trim.left == false) {
    xmin = 0;
  }
  if (sides & Trim.right == false) {
    xmax = w - 1;
  }

  w = 1 + xmax - xmin; // Image width in pixels
  h = 1 + ymax - ymin; // Image height in pixels

  return [xmin, ymin, w, h];
}