Use the longer structure vector to determine text line direction

manga_translator/utils/generic.py

@@ -350,20 +350,22 @@ def xywh(self):
 def sort_pnts(pts: np.ndarray):
     '''
     Direction must be provided for sorting.
-    The largest pairwise vector of input points is used to determine the direction.
+    The longer structure vector (mean of long side vectors) of input points is used to determine the direction.
     It is reliable enough for text lines but not for blocks.
     '''
 
     if isinstance(pts, List):
         pts = np.array(pts)
     assert isinstance(pts, np.ndarray) and pts.shape == (4, 2)
-    diag_vec = pts[:, None] - pts[None]
-    diag_vec_norm = np.linalg.norm(diag_vec, axis=2)
-    diag_pnt_ids = np.unravel_index(np.argmax(diag_vec_norm), diag_vec_norm.shape)
-
-    diag_vec = diag_vec[diag_pnt_ids[0], diag_pnt_ids[1]]
-    diag_vec = np.abs(diag_vec)
-    is_vertical = diag_vec[0] <= diag_vec[1]
+    pairwise_vec = (pts[:, None] - pts[None]).reshape((16, -1))
+    pairwise_vec_norm = np.linalg.norm(pairwise_vec, axis=1)
+    long_side_ids = np.argsort(pairwise_vec_norm)[[8, 10]]
+    long_side_vecs = pairwise_vec[long_side_ids]
+    inner_prod = (long_side_vecs[0] * long_side_vecs[1]).sum()
+    if inner_prod < 0:
+        long_side_vecs[0] = -long_side_vecs[0]
+    struc_vec = np.abs(long_side_vecs.mean(axis=0))
+    is_vertical = struc_vec[0] <= struc_vec[1]
 
     if is_vertical:
         pts = pts[np.argsort(pts[:, 1])]