taskbar+area: Implement center alignment

src/taskbar/taskbar.c

@@ -153,7 +153,7 @@ void init_taskbar_panel(void *p)
 	panel->g_taskbar.area.parent = panel;
 	panel->g_taskbar.area.panel = panel;
 	panel->g_taskbar.area.size_mode = SIZE_BY_LAYOUT;
-	panel->g_taskbar.area.alignment = ALIGN_RIGHT;
+	panel->g_taskbar.area.alignment = ALIGN_CENTER;
 	panel->g_taskbar.area._resize = resize_taskbar;
 	panel->g_taskbar.area._draw_foreground = draw_taskbar;
 	panel->g_taskbar.area._on_change_layout = on_change_taskbar;

src/util/area.c

@@ -220,6 +220,45 @@ void size_by_layout (Area *a, int level)
 
 				pos -= a->paddingx;
 			}
+		} else if (a->alignment == ALIGN_CENTER) {
+
+            int children_size = 0;
+
+            for (l = a->list; l ; l = l->next) {
+				Area *child = ((Area*)l->data);
+				if (!child->on_screen)
+					continue;
+
+				children_size += panel_horizontal ? child->width : child->height;
+                children_size += (l == a->list) ? 0 : a->paddingx;
+			}
+
+            int pos = (panel_horizontal ? a->posx : a->posy) + a->bg->border.width + a->paddingxlr;
+            pos += ((panel_horizontal ? a->width : a->height) - children_size) / 2;
+
+            for (l = a->list; l ; l = l->next) {
+				Area *child = ((Area*)l->data);
+				if (!child->on_screen)
+					continue;
+
+				if (panel_horizontal) {
+					if (pos != child->posx) {
+						// pos changed => redraw
+						child->posx = pos;
+						child->on_changed = 1;
+					}
+				} else {
+					if (pos != child->posy) {
+						// pos changed => redraw
+						child->posy = pos;
+						child->on_changed = 1;
+					}
+				}
+
+				size_by_layout(child, level+1);
+
+				pos += panel_horizontal ? child->width + a->paddingx : child->height + a->paddingx;
+			}
 		}
 	}