Add clientAt api

src/commands.zig

@@ -34,3 +34,32 @@ pub fn focus(server: *Server, client: *Client) !void {
         &wlr_keyboard.modifiers,
     );
 }
+
+pub const ClientAtResult = struct {
+    view: *Client,
+    surface: *wlr.Surface,
+    x: f64,
+    y: f64,
+};
+pub fn clientAt(server: *Server, lx: f64, ly: f64) ?ClientAtResult {
+    var sx: f64 = undefined;
+    var sy: f64 = undefined;
+    if (server.scene.tree.node.at(lx, ly, &sx, &sy)) |node| {
+        if (node.type != .buffer) return null;
+        const scene_buffer = wlr.SceneBuffer.fromNode(node);
+        const scene_surface = wlr.SceneSurface.tryFromBuffer(scene_buffer) orelse return null;
+
+        var it: ?*wlr.SceneTree = node.parent;
+        while (it) |n| : (it = n.node.parent) {
+            if (@as(?*Client, @ptrFromInt(n.node.data))) |client| {
+                return ClientAtResult{
+                    .view = client,
+                    .surface = scene_surface.surface,
+                    .x = sx,
+                    .y = sy,
+                };
+            }
+        }
+    }
+    return null;
+}