From 1e3a1116eeb6410dc513637e55a8dfcf2d9252f3 Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Fri, 6 May 2022 21:28:25 +1000
Subject: [PATCH] Always draw first segment in each translucent polygon line

---
 .../imagedraw_polygon_1px_high_translucent.png    | Bin 0 -> 76 bytes
 Tests/test_imagedraw.py                           |  14 ++++++++++++++
 src/libImaging/Draw.c                             |   4 ++--
 3 files changed, 16 insertions(+), 2 deletions(-)
 create mode 100644 Tests/images/imagedraw_polygon_1px_high_translucent.png

diff --git a/Tests/images/imagedraw_polygon_1px_high_translucent.png b/Tests/images/imagedraw_polygon_1px_high_translucent.png
new file mode 100644
index 0000000000000000000000000000000000000000..8bbf9397c72a4352cf74c16b0fdae378d56065f3
GIT binary patch
literal 76
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ZVBpqfXcTz0dNNR&!PC{xWt~$(69E385JCU|

literal 0
HcmV?d00001

diff --git a/Tests/test_imagedraw.py b/Tests/test_imagedraw.py
index 6755d94b895..7f4a18c47bf 100644
--- a/Tests/test_imagedraw.py
+++ b/Tests/test_imagedraw.py
@@ -655,6 +655,20 @@ def test_polygon_1px_high():
     assert_image_equal_tofile(im, expected)
 
 
+def test_polygon_1px_high_translucent():
+    # Test drawing a translucent 1px high polygon
+    # Arrange
+    im = Image.new("RGB", (4, 3))
+    draw = ImageDraw.Draw(im, "RGBA")
+    expected = "Tests/images/imagedraw_polygon_1px_high_translucent.png"
+
+    # Act
+    draw.polygon([(1, 1), (1, 1), (3, 1), (3, 1)], (255, 0, 0, 127))
+
+    # Assert
+    assert_image_equal_tofile(im, expected)
+
+
 def test_polygon_translucent():
     # Arrange
     im = Image.new("RGB", (W, H))
diff --git a/src/libImaging/Draw.c b/src/libImaging/Draw.c
index 86cd6c3a058..543651f7fa6 100644
--- a/src/libImaging/Draw.c
+++ b/src/libImaging/Draw.c
@@ -419,7 +419,7 @@ draw_horizontal_lines(
         if (e[i].ymin == y && e[i].ymin == e[i].ymax) {
             int xmax;
             int xmin = e[i].xmin;
-            if (*x_pos < xmin) {
+            if (*x_pos != -1 && *x_pos < xmin) {
                 // Line would be after the current position
                 continue;
             }
@@ -540,7 +540,7 @@ polygon_generic(Imaging im, int n, Edge *e, int ink, int eofill, hline_handler h
         }
         qsort(xx, j, sizeof(float), x_cmp);
         if (hasAlpha == 1) {
-            int x_pos = 0;
+            int x_pos = j == 0 ? -1 : 0;
             for (i = 1; i < j; i += 2) {
                 int x_end = ROUND_DOWN(xx[i]);
                 if (x_end < x_pos) {