Bugfix: don’t overwrite the original size of floating windows when changing border style

fixes #1263

include/util.h

@@ -57,6 +57,7 @@ int min(int a, int b);
 int max(int a, int b);
 bool rect_contains(Rect rect, uint32_t x, uint32_t y);
 Rect rect_add(Rect a, Rect b);
+Rect rect_sub(Rect a, Rect b);
 
 /**
  * Returns true if the name consists of only digits.

src/con.c

@@ -1194,34 +1194,30 @@ void con_set_border_style(Con *con, int border_style, int border_width) {
 
     /* For floating containers, we want to keep the position/size of the
      * *window* itself. We first add the border pixels to con->rect to make
-     * con->rect represent the absolute position of the window. Then, we change
-     * the border and subtract the new border pixels. Afterwards, we update
-     * parent->rect to contain con. */
+     * con->rect represent the absolute position of the window (same for
+     * parent). Then, we change the border style and subtract the new border
+     * pixels. For the parent, we do the same also for the decoration. */
     DLOG("This is a floating container\n");
 
+    Con *parent = con->parent;
     Rect bsr = con_border_style_rect(con);
-    con->rect.x += bsr.x;
-    con->rect.y += bsr.y;
-    con->rect.width += bsr.width;
-    con->rect.height += bsr.height;
+    int deco_height = (con->border_style == BS_NORMAL ? render_deco_height() : 0);
+
+    con->rect = rect_add(con->rect, bsr);
+    parent->rect = rect_add(parent->rect, bsr);
+    parent->rect.y += deco_height;
+    parent->rect.height -= deco_height;
 
     /* Change the border style, get new border/decoration values. */
     con->border_style = border_style;
     con->current_border_width = border_width;
     bsr = con_border_style_rect(con);
-    int deco_height =
-        (con->border_style == BS_NORMAL ? render_deco_height() : 0);
+    deco_height = (con->border_style == BS_NORMAL ? render_deco_height() : 0);
 
-    con->rect.x -= bsr.x;
-    con->rect.y -= bsr.y;
-    con->rect.width -= bsr.width;
-    con->rect.height -= bsr.height;
-
-    Con *parent = con->parent;
-    parent->rect.x = con->rect.x;
-    parent->rect.y = con->rect.y - deco_height;
-    parent->rect.width = con->rect.width;
-    parent->rect.height = con->rect.height + deco_height;
+    con->rect = rect_sub(con->rect, bsr);
+    parent->rect = rect_sub(parent->rect, bsr);
+    parent->rect.y -= deco_height;
+    parent->rect.height += deco_height;
 }
 
 /*

src/util.c

@@ -48,6 +48,13 @@ Rect rect_add(Rect a, Rect b) {
                   a.height + b.height};
 }
 
+Rect rect_sub(Rect a, Rect b) {
+    return (Rect){a.x - b.x,
+                  a.y - b.y,
+                  a.width - b.width,
+                  a.height - b.height};
+}
+
 /*
  * Returns true if the name consists of only digits.
  *

testcases/t/181-regress-float-border.t

@@ -20,9 +20,8 @@
 # d805d1bbeaf89e11f67c981f94c9f55bbb4b89d9
 #
 use i3test;
-use Data::Dumper;
 
-fresh_workspace;
+my $tmp = fresh_workspace;
 
 my $win = open_floating_window(rect => [10, 10, 200, 100]);
 
@@ -36,4 +35,23 @@ $geometry = $win->rect;
 is($geometry->{width}, 200, 'width correct');
 is($geometry->{height}, 100, 'height correct');
 
+################################################################################
+# When in fullscreen mode, the original position must not be overwritten.
+################################################################################
+
+sub get_floating_con_rect {
+    my ($nodes, $focus) = get_ws($tmp);
+    my $floating_con = $nodes->{floating_nodes}->[0];
+    return $floating_con->{rect};
+}
+my $old_rect = get_floating_con_rect();
+
+cmd 'fullscreen';
+
+is_deeply(get_floating_con_rect(), $old_rect, 'Rect the same after going into fullscreen');
+
+cmd 'border pixel 2';
+
+is_deeply(get_floating_con_rect(), $old_rect, 'Rect the same after changing border style');
+
 done_testing;