create hide_edge_borders option

src/cfgparse.l

@@ -200,6 +200,7 @@ new_float                       { return TOKNEWFLOAT; }
 normal                          { return TOK_NORMAL; }
 none                            { return TOK_NONE; }
 1pixel                          { return TOK_1PIXEL; }
+hide_edge_borders               { return TOK_HIDE_EDGE_BORDERS; }
 focus_follows_mouse             { return TOKFOCUSFOLLOWSMOUSE; }
 force_focus_wrapping            { return TOK_FORCE_FOCUS_WRAPPING; }
 force_xinerama                  { return TOK_FORCE_XINERAMA; }

src/cfgparse.y

@@ -735,6 +735,7 @@ void parse_file(const char *f) {
 %token                  TOK_NORMAL                  "normal"
 %token                  TOK_NONE                    "none"
 %token                  TOK_1PIXEL                  "1pixel"
+%token                  TOK_HIDE_EDGE_BORDERS       "hide_edge_borders"
 %token                  TOKFOCUSFOLLOWSMOUSE        "focus_follows_mouse"
 %token                  TOK_FORCE_FOCUS_WRAPPING    "force_focus_wrapping"
 %token                  TOK_FORCE_XINERAMA          "force_xinerama"
@@ -833,6 +834,7 @@ line:
     | workspace_layout
     | new_window
     | new_float
+    | hide_edge_borders
     | focus_follows_mouse
     | force_focus_wrapping
     | force_xinerama
@@ -1474,6 +1476,14 @@ bool:
     }
     ;
 
+hide_edge_borders:
+    TOK_HIDE_EDGE_BORDERS bool
+    {
+        DLOG("hide edge borders = %d\n", $2);
+        config.hide_edge_borders = $2;
+    }
+    ;
+
 focus_follows_mouse:
     TOKFOCUSFOLLOWSMOUSE bool
     {

src/con.c

@@ -934,12 +934,32 @@ Con *con_descend_direction(Con *con, direction_t direction) {
  *
  */
 Rect con_border_style_rect(Con *con) {
+    adjacent_t adjacent_to = ADJ_NONE;
+    Rect result;
+    if (config.hide_edge_borders)
+        adjacent_to = con_adjacent_borders(con);
     switch (con_border_style(con)) {
     case BS_NORMAL:
-        return (Rect){2, 0, -(2 * 2), -2};
+        result = (Rect){2, 0, -(2 * 2), -2};
+        if (adjacent_to & ADJ_LEFT_SCREEN_EDGE) {
+            result.x -= 2;
+            result.width += 2;
+        }
+        if (adjacent_to & ADJ_RIGHT_SCREEN_EDGE) {
+            result.width += 2;
+        }
+        return result;
 
     case BS_1PIXEL:
-        return (Rect){1, 1, -2, -2};
+        result = (Rect){1, 1, -2, -2};
+        if (adjacent_to & ADJ_LEFT_SCREEN_EDGE) {
+            result.x -= 1;
+            result.width += 1;
+        }
+        if (adjacent_to & ADJ_RIGHT_SCREEN_EDGE) {
+            result.width += 1;
+        }
+        return result;
 
     case BS_NONE:
         return (Rect){0, 0, 0, 0};
@@ -949,6 +969,20 @@ Rect con_border_style_rect(Con *con) {
     }
 }
 
+/*
+ * Returns adjacent borders of the window. We need this if hide_edge_borders is
+ * enabled.
+ */
+adjacent_t con_adjacent_borders(Con *con) {
+    adjacent_t result = ADJ_NONE;
+    Con *output = con_get_output(con);
+    if (con->rect.x == output->rect.x)
+        result |= ADJ_LEFT_SCREEN_EDGE;
+    if (con->rect.x + con->rect.width == output->rect.x + output->rect.width)
+        result |= ADJ_RIGHT_SCREEN_EDGE;
+    return result;
+}
+
 /*
  * Use this function to get a container’s border style. This is important
  * because when inside a stack, the border style is always BS_NORMAL.

src/x.c

@@ -299,6 +299,9 @@ void x_window_kill(xcb_window_t window, kill_window_t kill_window) {
 void x_draw_decoration(Con *con) {
     Con *parent = con->parent;
     bool leaf = con_is_leaf(con);
+    adjacent_t adjacent_to = ADJ_NONE;
+    if (config.hide_edge_borders)
+        adjacent_to = con_adjacent_borders(con);
     /* This code needs to run for:
      *  • leaf containers
      *  • non-leaf containers which are in a stacked/tabbed container
@@ -408,12 +411,16 @@ void x_draw_decoration(Con *con) {
          * rectangle because some childs are not freely resizable and we want
          * their background color to "shine through". */
         xcb_change_gc(conn, con->pm_gc, XCB_GC_FOREGROUND, (uint32_t[]){ p->color->background });
-        xcb_rectangle_t borders[] = {
-            { 0, 0, br.x, r->height },
-            { 0, r->height + br.height + br.y, r->width, r->height },
-            { r->width + br.width + br.x, 0, r->width, r->height }
-        };
-        xcb_poly_fill_rectangle(conn, con->pixmap, con->pm_gc, 3, borders);
+        if (!(adjacent_to & ADJ_LEFT_SCREEN_EDGE)) {
+            xcb_rectangle_t leftline = { 0, 0, br.x, r->height };
+            xcb_poly_fill_rectangle(conn, con->pixmap, con->pm_gc, 1, &leftline);
+        }
+        if (!(adjacent_to & ADJ_RIGHT_SCREEN_EDGE)) {
+            xcb_rectangle_t rightline = { r->width + br.width + br.x, 0, r->width, r->height };
+            xcb_poly_fill_rectangle(conn, con->pixmap, con->pm_gc, 1, &rightline);
+        }
+        xcb_rectangle_t bottomline = { 0, r->height + br.height + br.y, r->width, r->height };
+        xcb_poly_fill_rectangle(conn, con->pixmap, con->pm_gc, 1, &bottomline);
         /* 1pixel border needs an additional line at the top */
         if (p->border_style == BS_1PIXEL) {
             xcb_rectangle_t topline = { br.x, 0, con->rect.width + br.width + br.x, br.y };