From 056dc89a3c85cbd6d6c960cbfc5aaa52f996bd3d Mon Sep 17 00:00:00 2001
From: Andrew Murray <3112309+radarhere@users.noreply.github.com>
Date: Tue, 10 Jun 2025 22:12:40 +1000
Subject: [PATCH] Correct drawing I;16 horizontal lines (#8985)

---
 Tests/images/imagedraw_rectangle_I.tiff | Bin 20122 -> 20122 bytes
 Tests/test_imagedraw.py                 |   3 ++-
 src/libImaging/Draw.c                   |  34 +++++++++++++++---------
 3 files changed, 23 insertions(+), 14 deletions(-)

diff --git a/Tests/images/imagedraw_rectangle_I.tiff b/Tests/images/imagedraw_rectangle_I.tiff
index 9b9eda883a371d9cc88b4677b09d2e351c42e609..f0cb534b63e47c940ecb6c3323cb9de3dce573d4 100644
GIT binary patch
literal 20122
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z2oNAZfB*pk1b$Lr9KP}V{8t|bpOFf%N~Nk;vC0MV(ymzL0(ogyta5?8v@2G*KwjDv
zt6U&2?TS?{ke7DFDi_F0yJD3K<fUD)$_4V$u2|&)d1+Uya)G?GD^|HcUfLC_Tp%y)
vid8O<mv+S}7s$*1+0}piA1?pplmrM6AV7cs0RjXF5FkK+009C7-W7NNFeP4m

literal 20122
zcmeI&F$%&!6h+Y=Bch!)+E`e-lQgcvRk-;$N{W=PF$6gQVHmDR4zF|=?zOL~Lshq}
zuAQFk)6LGCuK(U2+kHQsKizJ2K280r-JfUQy-erZqv|^ATjn7^fB*pk1PBlyK!5-N
z0t5&UAV6T10^=gj?_Yf!{YEOlDwV2Y#VQxbOS@u~3*@C;vC0MV(ymzL0(ogyta5?8
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qUfLC_Tp%z1XID%7Aue}S5+Fc;009C72oNAZfB*pk1PBmVzrY)UtC9==

diff --git a/Tests/test_imagedraw.py b/Tests/test_imagedraw.py
index ffe9c0979..37669a2e5 100644
--- a/Tests/test_imagedraw.py
+++ b/Tests/test_imagedraw.py
@@ -783,9 +783,10 @@ def test_rectangle_I16(bbox: Coords) -> None:
     draw = ImageDraw.Draw(im)
 
     # Act
-    draw.rectangle(bbox, outline=0xFFFF)
+    draw.rectangle(bbox, outline=0xCDEF)
 
     # Assert
+    assert im.getpixel((X0, Y0)) == 0xCDEF
     assert_image_equal_tofile(im, "Tests/images/imagedraw_rectangle_I.tiff")
 
 
diff --git a/src/libImaging/Draw.c b/src/libImaging/Draw.c
index 70f267ae4..27cac687e 100644
--- a/src/libImaging/Draw.c
+++ b/src/libImaging/Draw.c
@@ -104,8 +104,6 @@ point32rgba(Imaging im, int x, int y, int ink) {
 
 static inline void
 hline8(Imaging im, int x0, int y0, int x1, int ink, Imaging mask) {
-    int pixelwidth;
-
     if (y0 >= 0 && y0 < im->ysize) {
         if (x0 < 0) {
             x0 = 0;
@@ -118,20 +116,30 @@ hline8(Imaging im, int x0, int y0, int x1, int ink, Imaging mask) {
             x1 = im->xsize - 1;
         }
         if (x0 <= x1) {
-            pixelwidth = strncmp(im->mode, "I;16", 4) == 0 ? 2 : 1;
-            if (mask == NULL) {
-                memset(
-                    im->image8[y0] + x0 * pixelwidth,
-                    (UINT8)ink,
-                    (x1 - x0 + 1) * pixelwidth
-                );
+            int bigendian = -1;
+            if (strncmp(im->mode, "I;16", 4) == 0) {
+                bigendian =
+                    (
+#ifdef WORDS_BIGENDIAN
+                        strcmp(im->mode, "I;16") == 0 || strcmp(im->mode, "I;16L") == 0
+#else
+                        strcmp(im->mode, "I;16B") == 0
+#endif
+                    )
+                        ? 1
+                        : 0;
+            }
+            if (mask == NULL && bigendian == -1) {
+                memset(im->image8[y0] + x0, (UINT8)ink, (x1 - x0 + 1));
             } else {
                 UINT8 *p = im->image8[y0];
                 while (x0 <= x1) {
-                    if (mask->image8[y0][x0]) {
-                        p[x0 * pixelwidth] = ink;
-                        if (pixelwidth == 2) {
-                            p[x0 * pixelwidth + 1] = ink;
+                    if (mask == NULL || mask->image8[y0][x0]) {
+                        if (bigendian == -1) {
+                            p[x0] = ink;
+                        } else {
+                            p[x0 * 2 + (bigendian ? 1 : 0)] = ink;
+                            p[x0 * 2 + (bigendian ? 0 : 1)] = ink >> 8;
                         }
                     }
                     x0++;