flag.dart

copyFlagToPicture(
    Matrix4 transform, Size deviceSize, img.Image flag, img.Image pic) async {
  print("device: " + deviceSize.toString());
  var d_flag_scale = deviceSize.width / flag.width;
  var d_flag_height = flag.height * d_flag_scale;
  print("d_flag_height: " + d_flag_height.toString());
  var d_flag_top = deviceSize.height / 2.0 - (d_flag_height / 2.0);
  var d_flag_bottom = deviceSize.height / 2.0 + (d_flag_height / 2.0);
  Vector4 vd_flag_lt = transform * (new Vector4(0.0, d_flag_top, 0.0, 1.0));
  Vector4 vd_flag_rt =
      transform * (new Vector4(deviceSize.width, d_flag_top, 0.0, 1.0));
  Vector4 vd_flag_lb = transform * (new Vector4(0.0, d_flag_bottom, 0.0, 1.0));
  Vector4 vd_flag_rb =
      transform * (new Vector4(deviceSize.width, d_flag_bottom, 0.0, 1.0));

  print("LeftTop: " + vd_flag_lt.toString());
  print("RightTop: " + vd_flag_rt.toString());
  print("LeftBottom: " + vd_flag_lb.toString());
  print("RightBottom: " + vd_flag_rb.toString());

  // Compute the rotation angle and rotate the flag.

  var vd_flag_orient = (vd_flag_rt - vd_flag_lt).normalized();
  print("Orientation vector: " + vd_flag_orient.toString());
  var angle = atan2(vd_flag_orient.y, vd_flag_orient.x) * 180 / pi;
  print("Rotational angle: " + angle.toString());
  var flagRotated = img.copyRotate(flag, angle);
  print("FlagRotated: " +
      flagRotated.width.toString() +
      "x" +
      flagRotated.height.toString());

  // Find the flag bounding box.
  var d_flag_min_x =
      min(min(vd_flag_lt.x, vd_flag_rt.x), min(vd_flag_lb.x, vd_flag_rb.x));
  var d_flag_min_y =
      min(min(vd_flag_lt.y, vd_flag_rt.y), min(vd_flag_lb.y, vd_flag_rb.y));
  var d_flag_max_x =
      max(max(vd_flag_lt.x, vd_flag_rt.x), max(vd_flag_lb.x, vd_flag_rb.x));
  var d_flag_max_y =
      max(max(vd_flag_lt.y, vd_flag_rt.y), max(vd_flag_lb.y, vd_flag_rb.y));

  print("bounding box:");
  print("  x: " + d_flag_min_x.toString() + " - " + d_flag_max_x.toString());
  print("  y: " + d_flag_min_y.toString() + " - " + d_flag_max_y.toString());

  var d_flag_w = d_flag_max_x - d_flag_min_x;
  var d_flag_h = d_flag_max_y - d_flag_min_y;

  print("  w: " + d_flag_w.toString() + ", h: " + d_flag_h.toString());

  // Determine relative bounds on the rotated flag image to copy to the picture.

  pic = img.copyRotate(pic, 90);
  print("rotated pic size: " +
      pic.width.toString() +
      "x" +
      pic.height.toString());

  var dp_scale_x = pic.width / deviceSize.width;
  var dp_scale_y = pic.height / deviceSize.height;
  print("device scale: x: " +
      dp_scale_x.toString() +
      ", y: " +
      dp_scale_y.toString());

  var p_flag_min_x = d_flag_min_x * dp_scale_x;
  var p_flag_max_x = d_flag_max_x * dp_scale_x;
  var p_flag_min_y = d_flag_min_y * dp_scale_y;
  var p_flag_max_y = d_flag_max_y * dp_scale_y;
  var p_flag_w = (p_flag_max_x - p_flag_min_x).toInt();
  var p_flag_h = (p_flag_max_y - p_flag_min_y).toInt();

  var flagResized =
      img.copyResize(flagRotated, width: p_flag_w, height: p_flag_h);
  print("resized flag size: " +
      flagResized.width.toString() +
      "x" +
      flagResized.height.toString());

  print("copy flag source:");
  print(
      "dst: x: " + p_flag_min_x.toString() + ", y: " + p_flag_min_y.toString());
  img.copyInto(
    pic,
    flagResized,
    dstX: p_flag_min_x.toInt(),
    dstY: p_flag_min_y.toInt(),
  );