From: Martin Rudalics <rudalics@gmx.at>
Date: Mon, 20 Nov 2017 08:18:59 +0000 (+0100)
Subject: Fix misbehavior when drawing three-pixel high horizontal dividers (Bug#29353)
X-Git-Tag: emacs-26.0.91~283^2
X-Git-Url: http://git.eshelyaron.com/gitweb/?a=commitdiff_plain;h=4da87999c234155300b30b01c5a7e221d65e4cc8;p=emacs.git

Fix misbehavior when drawing three-pixel high horizontal dividers (Bug#29353)

* src/xterm.c (x_draw_window_divider):
* src/w32term.c (w32_draw_window_divider): Fix misbehavior when
drawing three-pixel high horizontal dividers (Bug#29353).

The misbehavior was noted by Keith David Bershatsky and analyzed by Alan
Third.
---

diff --git a/src/w32term.c b/src/w32term.c
index e62d49dd947..7a3b2cc631f 100644
--- a/src/w32term.c
+++ b/src/w32term.c
@@ -660,21 +660,25 @@ w32_draw_window_divider (struct window *w, int x0, int x1, int y0, int y1)
 			      ? face_last->foreground
 			      : FRAME_FOREGROUND_PIXEL (f));
 
-  if (y1 - y0 > x1 - x0 && x1 - x0 > 2)
-    /* Vertical.  */
+  if ((y1 - y0 > x1 - x0) && (x1 - x0 >= 3))
+    /* A vertical divider, at least three pixels wide: Draw first and
+       last pixels differently.  */
     {
       w32_fill_area_abs (f, hdc, color_first, x0, y0, x0 + 1, y1);
       w32_fill_area_abs (f, hdc, color, x0 + 1, y0, x1 - 1, y1);
       w32_fill_area_abs (f, hdc, color_last, x1 - 1, y0, x1, y1);
     }
-  else if (x1 - x0 > y1 - y0 && y1 - y0 > 3)
-    /* Horizontal.  */
+  else if ((x1 - x0 > y1 - y0) && (y1 - y0 >= 3))
+    /* A horizontal divider, at least three pixels high: Draw first and
+       last pixels differently.  */
     {
       w32_fill_area_abs (f, hdc, color_first, x0, y0, x1, y0 + 1);
       w32_fill_area_abs (f, hdc, color, x0, y0 + 1, x1, y1 - 1);
       w32_fill_area_abs (f, hdc, color_last, x0, y1 - 1, x1, y1);
     }
   else
+    /* In any other case do not draw the first and last pixels
+       differently.  */
     w32_fill_area_abs (f, hdc, color, x0, y0, x1, y1);
 
   release_frame_dc (f, hdc);
diff --git a/src/xterm.c b/src/xterm.c
index 28abfaecde9..1deb7b46013 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -1104,8 +1104,9 @@ x_draw_window_divider (struct window *w, int x0, int x1, int y0, int y1)
 			      : FRAME_FOREGROUND_PIXEL (f));
   Display *display = FRAME_X_DISPLAY (f);
 
-  if (y1 - y0 > x1 - x0 && x1 - x0 > 2)
-    /* Vertical.  */
+  if ((y1 - y0 > x1 - x0) && (x1 - x0 >= 3))
+    /* A vertical divider, at least three pixels wide: Draw first and
+       last pixels differently.  */
     {
       XSetForeground (display, f->output_data.x->normal_gc, color_first);
       x_fill_rectangle (f, f->output_data.x->normal_gc,
@@ -1117,8 +1118,9 @@ x_draw_window_divider (struct window *w, int x0, int x1, int y0, int y1)
       x_fill_rectangle (f, f->output_data.x->normal_gc,
 			x1 - 1, y0, 1, y1 - y0);
     }
-  else if (x1 - x0 > y1 - y0 && y1 - y0 > 3)
-    /* Horizontal.  */
+  else if ((x1 - x0 > y1 - y0) && (y1 - y0 >= 3))
+    /* A horizontal divider, at least three pixels high: Draw first and
+       last pixels differently.  */
     {
       XSetForeground (display, f->output_data.x->normal_gc, color_first);
       x_fill_rectangle (f, f->output_data.x->normal_gc,
@@ -1132,6 +1134,8 @@ x_draw_window_divider (struct window *w, int x0, int x1, int y0, int y1)
     }
   else
     {
+    /* In any other case do not draw the first and last pixels
+       differently.  */
       XSetForeground (display, f->output_data.x->normal_gc, color);
       x_fill_rectangle (f, f->output_data.x->normal_gc,
 			x0, y0, x1 - x0, y1 - y0);