remove borders in tabbed and monocle

src/Wm.zig

@@ -809,9 +809,21 @@ const tiled_all: river.WindowV1.Edges = .{
     .bottom = true,
 };
 
-fn applyWindowState(self: *Wm) void {
-    const bw = config.border_width;
+/// How wide a border to give a window.
+///
+/// The stacking layouts show one window filling the whole area, so a border
+/// there frames the screen rather than separating anything from anything:
+/// monocle and tabbed get none, and a fullscreen window never had one.
+/// Floating windows keep theirs whatever the layout, since those really do
+/// overlap.
+fn borderWidth(win: *const Window) i32 {
+    if (win.fullscreen) return 0;
+    if (win.floating) return config.border_width;
+    const out = win.output orelse return config.border_width;
+    return if (out.stacked) 0 else config.border_width;
+}
 
+fn applyWindowState(self: *Wm) void {
     for (self.windows.items) |win| {
         if (win.closed) continue;
 
@@ -855,7 +867,7 @@ fn applyWindowState(self: *Wm) void {
 
         if (!win.visible) continue;
 
-        const content = win.cell.inset(bw);
+        const content = win.cell.inset(borderWidth(win));
         const w, const h = win.clampSize(content.width, content.height);
         if (w != win.proposed_width or h != win.proposed_height) {
             win.window.proposeDimensions(w, h);
@@ -872,7 +884,6 @@ fn applyWindowState(self: *Wm) void {
 
 fn render(self: *Wm) void {
     const gpa = self.gpa;
-    const bw = config.border_width;
 
     self.scratch_order.clearRetainingCapacity();
 
@@ -886,7 +897,7 @@ fn render(self: *Wm) void {
             self.setHidden(win, !show);
             if (!show) continue;
 
-            self.place(win, bw);
+            self.place(win, borderWidth(win));
             self.scratch_order.append(gpa, win) catch {};
         }
 
@@ -927,7 +938,7 @@ fn render(self: *Wm) void {
         }
         std.mem.sort(*Window, self.scratch_windows.items, {}, lessByFocus);
         for (self.scratch_windows.items) |win| {
-            self.place(win, bw);
+            self.place(win, borderWidth(win));
             self.scratch_order.append(gpa, win) catch {};
         }
 
@@ -970,6 +981,11 @@ fn place(self: *Wm, win: *Window, bw: i32) void {
     const content = win.cell.inset(bw);
     if (win.getNode()) |node| node.setPosition(content.x, content.y);
 
+    if (bw == 0) {
+        win.window.setBorders(.{}, 0, 0, 0, 0, 0);
+        return;
+    }
+
     const focused = self.isFocusedAnywhere(win);
     const rgba = if (focused) config.border_focused else config.border_normal;
     const ch = color.toChannels(rgba);