image/lib/src/transform/copy_rectify.dart

import '../image.dart';
import '../util/point.dart';

/// Returns a copy of the [src] image, where the given rectangle
/// has been mapped to the full image.
Image copyRectify(Image src, {Point topLeft, Point topRight, Point bottomLeft,
                  Point bottomRight, Image toImage}) {
  Image dst = toImage == null ? Image.from(src) : toImage;
  for (int y = 0; y < dst.height; ++y) {
    double v = y / (dst.height - 1);
    for (int x = 0; x < dst.width; ++x) {
      double u = x / (dst.width - 1);
      // bilinear interpolation
      Point srcPixelCoord = topLeft * (1 - u) * (1 - v) +
          topRight * (u) * (1 - v) +
          bottomLeft * (1 - u) * (v) +
          bottomRight * (u) * (v);
      var srcPixel = src.getPixel(srcPixelCoord.xi, srcPixelCoord.yi);
      dst.setPixel(x, y, srcPixel);
    }
  }
  return dst;
}