[ui] replace host session window with compact edge controls

apps/desktop/src/gui/application/server_window_state.h

@@ -14,8 +14,47 @@
 
 namespace crossdesk::server_window_state {
 
-inline int ReconcileSelectedController(const std::vector<std::string>& ids,
-                                       std::string* selected_id) {
+// All values use logical desktop coordinates (including negative monitor
+// origins). The bar's anchor is independent of the panel's changing height.
+struct Rect {
+  float x, y, width, height;
+};
+
+struct EdgeLayout {
+  Rect bar;
+  Rect panel;
+  bool above;
+};
+
+inline EdgeLayout PlacePanel(const Rect &screen, float position,
+                             float bar_width, float panel_height) {
+  constexpr float bar_height = 36;
+  constexpr float gap = 6;
+  constexpr float margin = 8;
+  const float travel = std::max(0.0f, screen.height - bar_height - 2 * margin);
+  const float top =
+      screen.y + margin + travel * std::clamp(position, 0.0f, 1.0f);
+  const float above = std::max(0.0f, top - screen.y - margin - gap);
+  const float below = std::max(0.0f, screen.y + screen.height - margin - top -
+                                         bar_height - gap);
+  const bool opens_above =
+      below < panel_height && (above >= panel_height || above > below);
+  const float height = std::min(panel_height, opens_above ? above : below);
+  const float width = std::min(225.0f, screen.width);
+  return {{screen.x + screen.width - bar_width, top, bar_width, bar_height},
+          {screen.x + screen.width - width,
+           opens_above ? top - gap - height : top + bar_height + gap, width,
+           height},
+          opens_above};
+}
+
+inline bool Contains(const Rect &rect, float x, float y) {
+  return x >= rect.x && y >= rect.y && x < rect.x + rect.width &&
+         y < rect.y + rect.height;
+}
+
+inline int ReconcileSelectedController(const std::vector<std::string> &ids,
+                                       std::string *selected_id) {
   if (!selected_id) {
     return 0;
   }
@@ -33,4 +72,4 @@ inline int ReconcileSelectedController(const std::vector<std::string>& ids,
 }
 } // namespace crossdesk::server_window_state
 
-#endif
+#endif