From b040240ecb8f07e4240135d5f1d51b493a47d53d Mon Sep 17 00:00:00 2001
From: Andrew Murray <radarhere@users.noreply.github.com>
Date: Sat, 4 Jan 2025 14:55:26 +1100
Subject: [PATCH] Improved connecting discontiguous corners

---
 .../discontiguous_corners_polygon.png         | Bin 533 -> 533 bytes
 Tests/test_imagedraw.py                       |   2 +-
 src/libImaging/Draw.c                         |  58 ++++++++----------
 3 files changed, 27 insertions(+), 33 deletions(-)

diff --git a/Tests/images/imagedraw/discontiguous_corners_polygon.png b/Tests/images/imagedraw/discontiguous_corners_polygon.png
index 1b58889c8f3ae45243a7509c907f1928534bcbde..8992a165758676b9ba7777347fb09a3b8c453e3d 100644
GIT binary patch
delta 498
zcmV<O0S*3@1eFAkEq_6>!!QU#x&NVZwfx<mj?>r}B*1oAc++Wu^hDyMmFv3h`#y7(
z^bX*wh={0kNqVm~ZJk<@{7}`frq38OUF0%$Ri9_ST)mw}n@*lB8`kG(v?=7-vMC9z
zPn)FNOFlq0L$jBBfNY*-7kRd9wq_%Fw(J<q)8yH*-@HyH&wrM!aXf)MTlTE)LFC!8
zJ+nq6?-zz7gK$tqK2nv3Jg_VIKS#VaCwYGgDr)x3pljw!tp?4{j|SxZ`AH;icI^v!
zjk`t2JH6}8yv97XN2ue!9Y^=e2D)tIu{r9I4{$+GjFBcSdF)&?)%TirHJK*QbAh37
z+&SD)PX+5I=6|Yw3PRo!R!u=@(yFB(Z9iKf1^G{PiTW3NlG%;C!G%4^PtC=)<n=CW
zPF^z?`;#BKa0>a(TpUFHEepqypH5182bmeUaqnc-s_XgQ{+#-eC+wU`t#9JT<STS<
zzn+=NubzUTsJWR>*W=9jlj!u-K3$uKcEi$mwNKY+qig+H7V^#a7ga8(`}`_7Z^}zP
zQ9q<-<PNVs?WSA&-hK(?LfzXJ%=xoJ?o(Yg+D&f}Pjz)@H(eS38)T?R<=RXIPbMVi
oux?}SPmMdaPvL91U3%pD2eNxR+9QHbW&i*H07*qoM6N<$f~R%@U;qFB

delta 498
zcmV<O0S*3@1eFAkEq_ar!ypVqx&NWKnrAbWO5ri+*HU9f3wBBL`UwX+X}$OBy3Sl%
zc?S@xCgN%gy{gu>sx8egsg|Yw#I!ktma!{-pYw9{cA9Otc{FxdpQqV|m`7tnCY0Yc
zh}>&F0UN>WHJ^ZuV|JNGW22dk=F!+W%xd#!?5C`Y&7-j;iGLTEM`LSqPco0j_UtvF
zc|TaBnTP~M<};~0<^#KGm-vZS{wjg@Oab*XJUP5=3P_!s&8re=9e<X9nm4ERhj~f5
zB<7vj&Gx(`Jak4;@Bj2ZvR^i$%Vs`yj%MZ)Qji-%Oq0}n?7kRko;B`jqBf690YSL#
zJUmfPCG!L4ihq9!Ql1mCPC@FVu}wkQ*`8qv>QD8B{9Jc+$-AK5ydi~mnpf?M*P557
z@N)B#eer(t%M?yAKiL-tnSV;*IP>a^$~!1re}Az#u=?k@{eksw9&mD^TA$$8<{7%T
zU(d|ucb|eKly1+L^El`HZd84>FK6@E9$Xr)_T`*5+iTxtF+aS1Q}Pz|J-^GG59Kvq
z$RE;k<Oz@8_Rwwo*?tT120hyo&iTDV>|Gt3?V-1fyE-1*Ls!QC1{o@oTsl+9J2Pa?
o!@AA+ej3>3+2wVTOis1_06el#wiqRwUjP6A07*qoM6N<$f>{3oE&u=k

diff --git a/Tests/test_imagedraw.py b/Tests/test_imagedraw.py
index 5fc1c27661a..17a61116f91 100644
--- a/Tests/test_imagedraw.py
+++ b/Tests/test_imagedraw.py
@@ -1683,7 +1683,7 @@ def test_discontiguous_corners_polygon() -> None:
         BLACK,
     )
     expected = os.path.join(IMAGES_PATH, "discontiguous_corners_polygon.png")
-    assert_image_similar_tofile(img, expected, 1)
+    assert_image_equal_tofile(img, expected)
 
 
 def test_polygon2() -> None:
diff --git a/src/libImaging/Draw.c b/src/libImaging/Draw.c
index ea6f8805efb..d5aff8709f5 100644
--- a/src/libImaging/Draw.c
+++ b/src/libImaging/Draw.c
@@ -501,55 +501,49 @@ polygon_generic(
                     // Needed to draw consistent polygons
                     xx[j] = xx[j - 1];
                     j++;
-                } else if (current->dx != 0 && j % 2 == 1 &&
-                           roundf(xx[j - 1]) == xx[j - 1]) {
+                } else if ((ymin == current->ymin || ymin == current->ymax) &&
+                           current->dx != 0) {
                     // Connect discontiguous corners
                     for (k = 0; k < i; k++) {
                         Edge *other_edge = edge_table[k];
-                        if ((current->dx > 0 && other_edge->dx <= 0) ||
-                            (current->dx < 0 && other_edge->dx >= 0)) {
+                        if ((ymin != other_edge->ymin && ymin != other_edge->ymax) ||
+                            other_edge->dx == 0) {
                             continue;
                         }
                         // Check if the two edges join to make a corner
-                        if (xx[j - 1] ==
-                            (ymin - other_edge->y0) * other_edge->dx + other_edge->x0) {
+                        if (roundf(xx[j - 1]) ==
+                            roundf(
+                                (ymin - other_edge->y0) * other_edge->dx +
+                                other_edge->x0
+                            )) {
                             // Determine points from the edges on the next row
                             // Or if this is the last row, check the previous row
-                            int offset = ymin == ymax ? -1 : 1;
+                            int offset = ymin == current->ymax ? -1 : 1;
                             adjacent_line_x =
                                 (ymin + offset - current->y0) * current->dx +
                                 current->x0;
-                            adjacent_line_x_other_edge =
-                                (ymin + offset - other_edge->y0) * other_edge->dx +
-                                other_edge->x0;
-                            if (ymin == current->ymax) {
-                                if (current->dx > 0) {
-                                    xx[k] =
-                                        fmax(
+                            if (ymin + offset >= other_edge->ymin &&
+                                ymin + offset <= other_edge->ymax) {
+                                adjacent_line_x_other_edge =
+                                    (ymin + offset - other_edge->y0) * other_edge->dx +
+                                    other_edge->x0;
+                                if (xx[j - 1] > adjacent_line_x + 1 &&
+                                    xx[j - 1] > adjacent_line_x_other_edge + 1) {
+                                    xx[j - 1] =
+                                        roundf(fmax(
                                             adjacent_line_x, adjacent_line_x_other_edge
-                                        ) +
+                                        )) +
                                         1;
-                                } else {
-                                    xx[k] =
-                                        fmin(
+                                } else if (xx[j - 1] < adjacent_line_x - 1 &&
+                                           xx[j - 1] < adjacent_line_x_other_edge - 1) {
+                                    xx[j - 1] =
+                                        roundf(fmin(
                                             adjacent_line_x, adjacent_line_x_other_edge
-                                        ) -
-                                        1;
-                                }
-                            } else {
-                                if (current->dx > 0) {
-                                    xx[k] = fmin(
-                                        adjacent_line_x, adjacent_line_x_other_edge
-                                    );
-                                } else {
-                                    xx[k] =
-                                        fmax(
-                                            adjacent_line_x, adjacent_line_x_other_edge
-                                        ) +
+                                        )) -
                                         1;
                                 }
+                                break;
                             }
-                            break;
                         }
                     }
                 }