[host] add new D12 capture interface

Note, this capture interface is not yet feature complete but does seem
to be stable.

host/platform/Windows/capture/D12/backend.h

@@ -0,0 +1,59 @@
+/**
+ * Looking Glass
+ * Copyright © 2017-2024 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_D12_BACKEND_
+#define _H_D12_BACKEND_
+
+#include <stdbool.h>
+#include <d3d12.h>
+#include "interface/capture.h"
+
+typedef struct D12Backend
+{
+  // friendly name
+  const char * name;
+
+  // internal name
+  const char * codeName;
+
+  // creation/init/free
+  bool (*create)(unsigned frameBuffers);
+  bool (*init)(
+    bool                 debug,
+    ID3D12Device3      * device,
+    IDXGIAdapter1      * adapter,
+    IDXGIOutput        * output);
+  bool (*deinit)(void);
+  void (*free)(void);
+
+  // capture callbacks
+  CaptureResult    (*capture)(unsigned frameBufferIndex);
+  CaptureResult    (*sync   )(ID3D12CommandQueue * commandQueue);
+  ID3D12Resource * (*fetch  )(unsigned frameBufferIndex);
+}
+D12Backend;
+
+// apis for the backend
+void d12_updatePointer(
+  CapturePointer * pointer, void * shape, size_t shapeSize);
+
+extern D12Backend D12Backend_DD;
+
+#endif