new UI system

interfaces/Crafter.Graphics-UIHit.cppm

@@ -0,0 +1,50 @@
+/*
+Crafter®.Graphics
+Copyright (C) 2026 Catcrafts®
+catcrafts.net
+
+This library is free software; you can redistribute it and/or
+modify it under the terms of the GNU Lesser General Public
+License version 3.0 as published by the Free Software Foundation;
+
+This library is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
+Lesser General Public License for more details.
+
+You should have received a copy of the GNU Lesser General Public
+License along with this library; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301 USA
+*/
+export module Crafter.Graphics:UIHit;
+import std;
+import :UILength;
+import :UIWidget;
+
+export namespace Crafter::UI {
+    // Find the topmost widget whose computedRect contains (x, y).
+    // Children are visited in reverse order so later children (drawn on
+    // top) win ties. Returns nullptr if the point is outside `root`.
+    inline Widget* HitTest(Widget& root, float x, float y) {
+        if (!root.computedRect.Contains(x, y)) return nullptr;
+
+        // Search children in reverse — the last-added child is on top in
+        // our draw order, so it wins overlapping hits.
+        for (auto it = root.children_.rbegin(); it != root.children_.rend(); ++it) {
+            if (Widget* hit = HitTest(**it, x, y); hit) return hit;
+        }
+        return &root;
+    }
+
+    // Dispatch a click at (x, y) to the topmost widget under the cursor,
+    // bubbling to ancestors until one returns true (handled). The default
+    // Widget::OnMouseClick returns false, so leaf widgets that don't care
+    // automatically defer to their parents.
+    inline void DispatchClick(Widget& root, float x, float y) {
+        Widget* target = HitTest(root, x, y);
+        while (target) {
+            if (target->OnMouseClick(x, y)) return;
+            target = target->parent;
+        }
+    }
+}