From 24388addb647dbb7599bfefa739d56c7a180e8f8 Mon Sep 17 00:00:00 2001
From: yo1995 <cht@bupt.edu.cn>
Date: Mon, 6 Aug 2018 18:13:57 +0800
Subject: [PATCH] feature improvement: improved performance of
 ImageDraw.floodfill with Python built-in set() datatype.

---
 src/PIL/ImageDraw.py | 52 ++++++++++++++++++++++++++------------------
 1 file changed, 31 insertions(+), 21 deletions(-)

diff --git a/src/PIL/ImageDraw.py b/src/PIL/ImageDraw.py
index ca8c1d17b..2db19af18 100644
--- a/src/PIL/ImageDraw.py
+++ b/src/PIL/ImageDraw.py
@@ -325,22 +325,23 @@ def getdraw(im=None, hints=None):
 
 def floodfill(image, xy, value, border=None, thresh=0):
     """
-    (experimental) Fills a bounded region with a given color.
+        (experimental) Fills a bounded region with a given color.
 
-    :param image: Target image.
-    :param xy: Seed position (a 2-item coordinate tuple). See
-        :ref:`coordinate-system`.
-    :param value: Fill color.
-    :param border: Optional border value.  If given, the region consists of
-        pixels with a color different from the border color.  If not given,
-        the region consists of pixels having the same color as the seed
-        pixel.
-    :param thresh: Optional threshold value which specifies a maximum
-        tolerable difference of a pixel value from the 'background' in
-        order for it to be replaced. Useful for filling regions of non-
-        homogeneous, but similar, colors.
-    """
+        :param image: Target image.
+        :param xy: Seed position (a 2-item coordinate tuple). See
+            :ref:`coordinate-system`.
+        :param value: Fill color.
+        :param border: Optional border value.  If given, the region consists of
+            pixels with a color different from the border color.  If not given,
+            the region consists of pixels having the same color as the seed
+            pixel.
+        :param thresh: Optional threshold value which specifies a maximum
+            tolerable difference of a pixel value from the 'background' in
+            order for it to be replaced. Useful for filling regions of non-
+            homogeneous, but similar, colors.
+        """
     # based on an implementation by Eric S. Raymond
+    # amended by yo1995 @20180806
     pixel = image.load()
     x, y = xy
     try:
@@ -350,12 +351,15 @@ def floodfill(image, xy, value, border=None, thresh=0):
         pixel[x, y] = value
     except (ValueError, IndexError):
         return  # seed point outside image
-    edge = [(x, y)]
+    edge = {(x, y)}
+    full_edge = set()  # use a set to record each unique pixel processed
     if border is None:
         while edge:
-            newedge = []
-            for (x, y) in edge:
+            new_edge = set()
+            for (x, y) in edge:  # 4 adjacent method
                 for (s, t) in ((x+1, y), (x-1, y), (x, y+1), (x, y-1)):
+                    if (s, t) in full_edge:
+                        continue  # if already processed, skip
                     try:
                         p = pixel[s, t]
                     except IndexError:
@@ -363,13 +367,17 @@ def floodfill(image, xy, value, border=None, thresh=0):
                     else:
                         if _color_diff(p, background) <= thresh:
                             pixel[s, t] = value
-                            newedge.append((s, t))
-            edge = newedge
+                            new_edge.add((s, t))
+                            full_edge.add((s, t))
+            full_edge = edge  # do not record useless pixels to reduce memory consumption
+            edge = new_edge
     else:
         while edge:
-            newedge = []
+            new_edge = set()
             for (x, y) in edge:
                 for (s, t) in ((x+1, y), (x-1, y), (x, y+1), (x, y-1)):
+                    if (s, t) in full_edge:
+                        continue
                     try:
                         p = pixel[s, t]
                     except IndexError:
@@ -377,7 +385,9 @@ def floodfill(image, xy, value, border=None, thresh=0):
                     else:
                         if p != value and p != border:
                             pixel[s, t] = value
-                            newedge.append((s, t))
+                            new_edge.add((s, t))
+                            full_edge.add((s, t))
+            full_edge = edge
             edge = newedge