Implement borderless / 1-px-bordered windows

Use bn (normal), bp (1-px), bb (borderless) as commands to change the
border style of the currently focused window. Feel free to use i3-msg
to do this.

include/client.h

@@ -78,4 +78,11 @@ void client_set_below_floating(xcb_connection_t *conn, Client *client);
  */
 bool client_is_floating(Client *client);
 
+/**
+ * Change the border type for the given client to normal (n), 1px border (p) or
+ * completely borderless (b).
+ *
+ */
+void client_change_border(xcb_connection_t *conn, Client *client, char border_type);
+
 #endif

include/data.h

@@ -360,6 +360,10 @@ struct Client {
          * initialization later */
         enum { TITLEBAR_TOP = 0, TITLEBAR_LEFT, TITLEBAR_RIGHT, TITLEBAR_BOTTOM, TITLEBAR_OFF } titlebar_position;
 
+        /** Contains a bool specifying whether this window should not be drawn
+         * with the usual decorations */
+        bool borderless;
+
         /** If a client is set as a dock, it is placed at the very bottom of
          * the screen and its requested size is used */
         bool dock;

src/client.c

@@ -248,3 +248,42 @@ void client_set_below_floating(xcb_connection_t *conn, Client *client) {
 bool client_is_floating(Client *client) {
         return (client->floating >= FLOATING_AUTO_ON);
 }
+
+/*
+ * Change the border type for the given client to normal (n), 1px border (p) or
+ * completely borderless (b).
+ *
+ */
+void client_change_border(xcb_connection_t *conn, Client *client, char border_type) {
+        switch (border_type) {
+                case 'n':
+                        LOG("Changing to normal border\n");
+                        client->titlebar_position = TITLEBAR_TOP;
+                        client->borderless = false;
+                        break;
+                case 'p':
+                        LOG("Changing to 1px border\n");
+                        client->titlebar_position = TITLEBAR_OFF;
+                        client->borderless = false;
+                        break;
+                case 'b':
+                        LOG("Changing to borderless\n");
+                        client->titlebar_position = TITLEBAR_OFF;
+                        client->borderless = true;
+                        break;
+                default:
+                        LOG("Unknown border mode\n");
+                        return;
+        }
+
+        /* Ensure that the child’s position inside our window gets updated */
+        client->force_reconfigure = true;
+
+        /* For clients inside a container, we can simply render the container.
+         * If the client is floating, we need to render the whole layout */
+        if (client->container != NULL)
+                render_container(conn, client->container);
+        else render_layout(conn);
+
+        redecorate_window(conn, client);
+}

src/commands.c

@@ -967,6 +967,16 @@ void parse_command(xcb_connection_t *conn, const char *command) {
                 return;
         }
 
+        /* Is it 'bn' (border normal), 'bp' (border 1pixel) or 'bb' (border borderless)? */
+        if (command[0] == 'b') {
+                if (last_focused == NULL) {
+                        LOG("No window focused, cannot change border type\n");
+                        return;
+                }
+                client_change_border(conn, last_focused, command[1]);
+                return;
+        }
+
         if (command[0] == 'H') {
                 LOG("Hiding all floating windows\n");
                 floating_toggle_hide(conn, c_ws);

src/layout.c

@@ -145,10 +145,12 @@ void decorate_window(xcb_connection_t *conn, Client *client, xcb_drawable_t draw
                 xcb_poly_fill_rectangle(conn, client->frame, client->titlegc, 1, &crect);
         }
 
-        /* Draw the lines */
-        xcb_draw_line(conn, drawable, gc, color->border, 0, offset, client->rect.width, offset);
-        xcb_draw_line(conn, drawable, gc, color->border, 2, offset + font->height + 3,
-                      client->rect.width - 3, offset + font->height + 3);
+        if (client->titlebar_position != TITLEBAR_OFF) {
+                /* Draw the lines */
+                xcb_draw_line(conn, drawable, gc, color->border, 0, offset, client->rect.width, offset);
+                xcb_draw_line(conn, drawable, gc, color->border, 2, offset + font->height + 3,
+                              client->rect.width - 3, offset + font->height + 3);
+        }
 
         /* If the client has a title, we draw it */
         if (client->name != NULL) {
@@ -227,11 +229,16 @@ void resize_client(xcb_connection_t *conn, Client *client) {
                         rect->height = client->rect.height - 2;
                         break;
                 default:
-                        if (client->titlebar_position == TITLEBAR_OFF) {
+                        if (client->titlebar_position == TITLEBAR_OFF && client->borderless) {
                                 rect->x = 0;
                                 rect->y = 0;
                                 rect->width = client->rect.width;
                                 rect->height = client->rect.height;
+                        } else if (client->titlebar_position == TITLEBAR_OFF && !client->borderless) {
+                                rect->x = 1;
+                                rect->y = 1;
+                                rect->width = client->rect.width - 1 - 1;
+                                rect->height = client->rect.height - 1 - 1;
                         } else {
                                 rect->x = 2;
                                 rect->y = font->height + 2 + 2;