From 2f7c2e973c723319431354d9b28163e66c0bb281 Mon Sep 17 00:00:00 2001
From: Lawrence37 <45837045+Lawrence37@users.noreply.github.com>
Date: Sun, 4 Feb 2024 15:40:38 -0800
Subject: [PATCH] Fix rotation of images with odd number of rows (#6926)

* Fix line in middle of 180 degree rotated image

For images with an odd number of rows, a 180 degree rotation resulted in
one row of un-rotated pixels because it was effectively rotated twice.

* Replace verbose swap with std::swap
---
 rtengine/iimage.h | 74 ++++++++++++++++++++++++++++++-----------------
 1 file changed, 47 insertions(+), 27 deletions(-)

diff --git a/rtengine/iimage.h b/rtengine/iimage.h
index 426b0c4c0..3e865bb2b 100644
--- a/rtengine/iimage.h
+++ b/rtengine/iimage.h
@@ -18,6 +18,7 @@
  */
 #pragma once
 
+#include <utility>
 #include <vector>
 
 #include <lcms2.h>
@@ -396,7 +397,7 @@ public:
 
             swap(rotatedImg);
         } else if (deg == 180) {
-            int height2 = height / 2 + (height & 1);
+            int height2 = height / 2;
 
 #ifdef _OPENMP
             // difficult to find a cutoff value where parallelization is counter productive because of processor's data cache collision...
@@ -406,13 +407,22 @@ public:
 
             for (int i = 0; i < height2; i++) {
                 for (int j = 0; j < width; j++) {
-                    T tmp;
                     int x = width - 1 - j;
                     int y = height - 1 - i;
 
-                    tmp = v(i, j);
-                    v(i, j) = v(y, x);
-                    v(y, x) = tmp;
+                    std::swap(v(i, j), v(y, x));
+                }
+            }
+
+            // Middle row of odd-height images: only go half way otherwise the
+            // pixels will be swapped twice.
+            if (height & 1) {
+                int i = height / 2;
+                int width2 = width / 2;
+                for (int j = 0; j < width2; j++) {
+                    int x = width - 1 - j;
+
+                    std::swap(v(i, j), v(i, x));
                 }
             }
 #ifdef _OPENMP
@@ -828,7 +838,7 @@ public:
 
             swap(rotatedImg);
         } else if (deg == 180) {
-            int height2 = height / 2 + (height & 1);
+            int height2 = height / 2;
 
 #ifdef _OPENMP
             // difficult to find a cutoff value where parallelization is counter productive because of processor's data cache collision...
@@ -838,21 +848,26 @@ public:
 
             for (int i = 0; i < height2; i++) {
                 for (int j = 0; j < width; j++) {
-                    T tmp;
                     int x = width - 1 - j;
                     int y = height - 1 - i;
 
-                    tmp = r(i, j);
-                    r(i, j) = r(y, x);
-                    r(y, x) = tmp;
+                    std::swap(r(i, j), r(y, x));
+                    std::swap(g(i, j), g(y, x));
+                    std::swap(b(i, j), b(y, x));
+                }
+            }
 
-                    tmp = g(i, j);
-                    g(i, j) = g(y, x);
-                    g(y, x) = tmp;
+            // Middle row of odd-height images: only go half way otherwise the
+            // pixels will be swapped twice.
+            if (height & 1) {
+                int i = height / 2;
+                int width2 = width / 2;
+                for (int j = 0; j < width2; j++) {
+                    int x = width - 1 - j;
 
-                    tmp = b(i, j);
-                    b(i, j) = b(y, x);
-                    b(y, x) = tmp;
+                    std::swap(r(i, j), r(i, x));
+                    std::swap(g(i, j), g(i, x));
+                    std::swap(b(i, j), b(i, x));
                 }
             }
 #ifdef _OPENMP
@@ -1481,26 +1496,31 @@ public:
 
             swap(rotatedImg);
         } else if (deg == 180) {
-            int height2 = height / 2 + (height & 1);
+            int height2 = height / 2;
 
             // Maybe not sufficiently optimized, but will do what it has to do
             for (int i = 0; i < height2; i++) {
                 for (int j = 0; j < width; j++) {
-                    T tmp;
                     int x = width - 1 - j;
                     int y = height - 1 - i;
 
-                    tmp = r(i, j);
-                    r(i, j) = r(y, x);
-                    r(y, x) = tmp;
+                    std::swap(r(i, j), r(y, x));
+                    std::swap(g(i, j), g(y, x));
+                    std::swap(b(i, j), b(y, x));
+                }
+            }
 
-                    tmp = g(i, j);
-                    g(i, j) = g(y, x);
-                    g(y, x) = tmp;
+            // Middle row of odd-height images: only go half way otherwise the
+            // pixels will be swapped twice.
+            if (height & 1) {
+                int i = height / 2;
+                int width2 = width / 2;
+                for (int j = 0; j < width2; j++) {
+                    int x = width - 1 - j;
 
-                    tmp = b(i, j);
-                    b(i, j) = b(y, x);
-                    b(y, x) = tmp;
+                    std::swap(r(i, j), r(i, x));
+                    std::swap(g(i, j), g(i, x));
+                    std::swap(b(i, j), b(i, x));
                 }
             }
         }