vr: add OpenXR headset output, VR tracker and VR controller input behind --vr (#1726)

src/graphics/presentation/openxrHeadset.h

@@ -0,0 +1,41 @@
+#ifndef EMULATOR_SRC_GRAPHICS_PRESENTATION_OPENXRHEADSET_H_
+#define EMULATOR_SRC_GRAPHICS_PRESENTATION_OPENXRHEADSET_H_
+
+#include "graphics/host_gpu/vulkanCommon.h"
+
+#include <vector>
+
+namespace Libs::Graphics {
+struct GraphicContext;
+struct VulkanImage;
+class CommandBuffer;
+} // namespace Libs::Graphics
+
+// Output to a real headset through OpenXR. Everything here is inert unless the virtual headset is
+// enabled (--vr) and an OpenXR runtime with a headset is available; KYTY_OPENXR=0 turns it off.
+namespace Libs::Vr {
+
+// Creates the OpenXR instance. Call before the Vulkan instance exists, because the runtime names
+// the Vulkan extensions and the GPU it needs.
+void OpenXrInit();
+
+// Appends the Vulkan instance or device extensions the runtime needs, when available.
+void OpenXrAppendExtensions(std::vector<const char*>&                   out,
+                            const std::vector<vk::ExtensionProperties>& available, bool device);
+
+// The physical device the runtime renders with. False when OpenXR is not in use.
+bool OpenXrPhysicalDevice(vk::Instance instance, vk::PhysicalDevice& out);
+
+// Creates the session and starts the headset thread. Call once the device and queue exist.
+void OpenXrStartSession(Graphics::GraphicContext& graphics);
+
+// Stops the headset thread and destroys the session. Call before the device is destroyed.
+void OpenXrShutdown();
+
+// Render thread, headset flips only: scales the side-by-side eye image into a staging image for the
+// headset thread. The source is in transfer-source layout.
+void OpenXrQueueEyeSource(Graphics::CommandBuffer& command, const Graphics::VulkanImage& source);
+
+} // namespace Libs::Vr
+
+#endif // EMULATOR_SRC_GRAPHICS_PRESENTATION_OPENXRHEADSET_H_