From 08b5a2e9a7d290f4cd2cfb35dd556d50145a7dea Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Sat, 8 Jun 2024 14:35:10 +1000
Subject: [PATCH] Corrected using a 1 mode mask with I;16* images

---
 Tests/images/imagedraw_polygon_width_I.tiff | Bin 0 -> 20122 bytes
 Tests/test_imagedraw.py                     |  13 ++++++++++
 src/libImaging/Paste.c                      |  26 +++++++++++++++++---
 3 files changed, 35 insertions(+), 4 deletions(-)
 create mode 100644 Tests/images/imagedraw_polygon_width_I.tiff

diff --git a/Tests/images/imagedraw_polygon_width_I.tiff b/Tests/images/imagedraw_polygon_width_I.tiff
new file mode 100644
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diff --git a/Tests/test_imagedraw.py b/Tests/test_imagedraw.py
index c221fe008..505bba80c 100644
--- a/Tests/test_imagedraw.py
+++ b/Tests/test_imagedraw.py
@@ -631,6 +631,19 @@ def test_polygon(points: Coords) -> None:
     assert_image_equal_tofile(im, "Tests/images/imagedraw_polygon.png")
 
 
+@pytest.mark.parametrize("points", POINTS)
+def test_polygon_width_I16(points: Coords) -> None:
+    # Arrange
+    im = Image.new("I;16", (W, H))
+    draw = ImageDraw.Draw(im)
+
+    # Act
+    draw.polygon(points, outline=0xFFFF, width=2)
+
+    # Assert
+    assert_image_equal_tofile(im, "Tests/images/imagedraw_polygon_width_I.tiff")
+
+
 @pytest.mark.parametrize("mode", ("RGB", "L"))
 @pytest.mark.parametrize("kite_points", KITE_POINTS)
 def test_polygon_kite(
diff --git a/src/libImaging/Paste.c b/src/libImaging/Paste.c
index a018225b2..dc67cb41d 100644
--- a/src/libImaging/Paste.c
+++ b/src/libImaging/Paste.c
@@ -65,15 +65,32 @@ paste_mask_1(
     int x, y;
 
     if (imOut->image8) {
+        int in_i16 = strncmp(imIn->mode, "I;16", 4) == 0;
+        int out_i16 = strncmp(imOut->mode, "I;16", 4) == 0;
         for (y = 0; y < ysize; y++) {
             UINT8 *out = imOut->image8[y + dy] + dx;
+            if (out_i16) {
+                out += dx;
+            }
             UINT8 *in = imIn->image8[y + sy] + sx;
+            if (in_i16) {
+                in += sx;
+            }
             UINT8 *mask = imMask->image8[y + sy] + sx;
             for (x = 0; x < xsize; x++) {
-                if (*mask++) {
+                if (*mask) {
                     *out = *in;
                 }
-                out++, in++;
+                if (in_i16) {
+                    in++;
+                }
+                if (out_i16) {
+                    out++;
+                    if (*mask) {
+                        *out = *in;
+                    }
+                }
+                out++, in++, mask++;
             }
         }
 
@@ -415,15 +432,16 @@ fill_mask_L(
     unsigned int tmp1;
 
     if (imOut->image8) {
+        int i16 = strncmp(imOut->mode, "I;16", 4) == 0;
         for (y = 0; y < ysize; y++) {
             UINT8 *out = imOut->image8[y + dy] + dx;
-            if (strncmp(imOut->mode, "I;16", 4) == 0) {
+            if (i16) {
                 out += dx;
             }
             UINT8 *mask = imMask->image8[y + sy] + sx;
             for (x = 0; x < xsize; x++) {
                 *out = BLEND(*mask, *out, ink[0], tmp1);
-                if (strncmp(imOut->mode, "I;16", 4) == 0) {
+                if (i16) {
                     out++;
                     *out = BLEND(*mask, *out, ink[1], tmp1);
                 }