[client] overlay: added new interface for overlay windows using ImGui

client/include/interface/overlay.h

@@ -0,0 +1,74 @@
+/**
+ * Looking Glass
+ * Copyright (C) 2017-2021 The Looking Glass Authors
+ * https://looking-glass.io
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by the Free
+ * Software Foundation; either version 2 of the License, or (at your option)
+ * any later version.
+ *
+ * This program 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 General Public License for
+ * more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc., 59
+ * Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ */
+
+#ifndef _H_I_OVERLAY_
+#define _H_I_OVERLAY_
+
+#include <stdbool.h>
+#include "common/types.h"
+
+enum LG_OverlayFlags
+{
+  /* requires mouse interaction */
+  LG_OVERLAY_INTERACTIVE = (1U << 1U),
+};
+
+struct LG_OverlayOps
+{
+  /* internal name of the overlay for debugging */
+  const char * name;
+
+  /* called when the overlay is registered */
+  bool (*init)(void ** udata, void * params);
+
+  /* final free */
+  void (*free)(void * udata);
+
+  /* general state flags, may be changed at any time */
+  enum LG_OverlayFlags flags;
+
+  /* get the number of windows that will be rendered when `render` is called
+   *
+   *`interactive` is true if the application is currently in ovelay interaction
+   * mode
+   */
+  int (*getWindowCount)(void * udata, bool interactive);
+
+  /* perform the actual drawing/rendering
+   *
+   * `interactive` is true if the application is currently in ovelay interaction
+   * mode.
+   *
+   * The caller provides `windowRects` to be populated by the callee and is sized
+   * according to the return value of `getWindowCount`
+   */
+  void (*render)(void * udata, bool interactive, struct Rect * windowRects[]);
+
+  /* TODO: add load/save settings capabillity */
+};
+
+#define ASSERT_LG_OVERLAY_VALID(x) \
+  assert((x)->name          ); \
+  assert((x)->init          ); \
+  assert((x)->free          ); \
+  assert((x)->getWindowCount); \
+  assert((x)->render        );
+
+#endif