copyResize function Null safety

Image copyResize(Image src, {int? width, int? height, Interpolation interpolation = Interpolation.nearest})

Returns a resized copy of the src image. If height isn't specified, then it will be determined by the aspect ratio of src and width. If width isn't specified, then it will be determined by the aspect ratio of src and height.

Implementation

Image copyResize(Image src,
    {int? width,
    int? height,
    Interpolation interpolation = Interpolation.nearest}) {
  if (width == null && height == null) {
    throw ImageException('Invalid size');
  }

  src = bakeOrientation(src);

  if (height == null || height <= 0) {
    height = (width! * (src.height / src.width)).toInt();
  }

  if (width == null || width <= 0) {
    width = (height * (src.width / src.height)).toInt();
  }

  if (width == src.width && height == src.height) {
    return src.clone();
  }

  final dst = Image(width, height,
      channels: src.channels, exif: src.exif, iccp: src.iccProfile);

  final dy = src.height / height;
  final dx = src.width / width;

  if (interpolation == Interpolation.average) {
    final sData = src.getBytes();
    final sw4 = src.width * 4;

    for (var y = 0; y < height; ++y) {
      final y1 = (y * dy).toInt();
      var y2 = ((y + 1) * dy).toInt();
      if (y2 == y1) {
        y2++;
      }

      for (var x = 0; x < width; ++x) {
        final x1 = (x * dx).toInt();
        var x2 = ((x + 1) * dx).toInt();
        if (x2 == x1) {
          x2++;
        }

        var r = 0;
        var g = 0;
        var b = 0;
        var a = 0;
        var np = 0;
        for (var sy = y1; sy < y2; ++sy) {
          var si = sy * sw4 + x1 * 4;
          for (var sx = x1; sx < x2; ++sx, ++np) {
            r += sData[si++];
            g += sData[si++];
            b += sData[si++];
            a += sData[si++];
          }
        }
        dst.setPixel(x, y, getColor(r ~/ np, g ~/ np, b ~/ np, a ~/ np));
      }
    }
  } else if (interpolation == Interpolation.nearest) {
    final scaleX = Int32List(width);
    for (var x = 0; x < width; ++x) {
      scaleX[x] = (x * dx).toInt();
    }
    for (var y = 0; y < height; ++y) {
      final y2 = (y * dy).toInt();
      for (var x = 0; x < width; ++x) {
        dst.setPixel(x, y, src.getPixel(scaleX[x], y2));
      }
    }
  } else {
    // Copy the pixels from this image to the new image.
    for (var y = 0; y < height; ++y) {
      final y2 = (y * dy);
      for (var x = 0; x < width; ++x) {
        final x2 = (x * dx);
        dst.setPixel(x, y, src.getPixelInterpolate(x2, y2, interpolation));
      }
    }
  }

  return dst;
}