From c4a201eaf4e7cf6ec8a76768e6bb27dcbe2e94f8 Mon Sep 17 00:00:00 2001
From: Ell <ell_se@yahoo.com>
Date: Fri, 12 Jun 2020 17:20:23 +0300
Subject: [PATCH] Issue #5208 - paint brush is broken when aspect ratio is set
 to negative

Fix horizontal downscaling of brush mipmap levels with odd width.
We'd previously fail to skip the last pixel of each input row,
which isn't included in the output when the width is odd, causing
subsequent output rows to be shifted to the right.
---
 app/core/gimpbrush-mipmap.cc | 17 ++++++++++++-----
 1 file changed, 12 insertions(+), 5 deletions(-)

diff --git a/app/core/gimpbrush-mipmap.cc b/app/core/gimpbrush-mipmap.cc
index ae394dc3e9..7c3b061130 100644
--- a/app/core/gimpbrush-mipmap.cc
+++ b/app/core/gimpbrush-mipmap.cc
@@ -292,16 +292,20 @@ struct MipmapAlgorithms
       [=] (gint offset,
            gint size)
       {
-        const T *src  = (const T *) gimp_temp_buf_get_data (source);
-        T       *dest = (T       *) gimp_temp_buf_get_data (destination);
+        const T *src0        = (const T *) gimp_temp_buf_get_data (source);
+        T       *dest0       = (T       *) gimp_temp_buf_get_data (destination);
+        gint     src_stride  = N * gimp_temp_buf_get_width (source);
+        gint     dest_stride = N * gimp_temp_buf_get_width (destination);
         gint     y;
 
-        src  += offset * gimp_temp_buf_get_width (source)      * N;
-        dest += offset * gimp_temp_buf_get_width (destination) * N;
+        src0  += offset * src_stride;
+        dest0 += offset * dest_stride;
 
         for (y = 0; y < size; y++)
           {
-            gint x;
+            const T *src  = src0;
+            T       *dest = dest0;
+            gint     x;
 
             for (x = 0; x < width; x++)
               {
@@ -313,6 +317,9 @@ struct MipmapAlgorithms
                 src  += 2 * N;
                 dest += N;
               }
+
+            src0  += src_stride;
+            dest0 += dest_stride;
           }
       });