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

src/graphics/presentation/vrInput.h

@@ -0,0 +1,36 @@
+#ifndef EMULATOR_SRC_GRAPHICS_PRESENTATION_VRINPUT_H_
+#define EMULATOR_SRC_GRAPHICS_PRESENTATION_VRINPUT_H_
+
+namespace Libs::Vr {
+
+// A pose in the tracking space: metres, right-handed, +y up, -z forward (the OpenXR convention).
+struct VrPose {
+	bool  valid          = false;
+	float orientation[4] = {0.0f, 0.0f, 0.0f, 1.0f}; // x, y, z, w
+	float position[3]    = {0.0f, 0.0f, 0.0f};
+};
+
+// One headset controller. Sticks are -1..1 with +y up, the trigger and squeeze 0..1.
+struct VrControllerInput {
+	bool   connected = false;
+	VrPose pose;
+	float  trigger     = 0.0f;
+	float  squeeze     = 0.0f;
+	float  stick_x     = 0.0f;
+	float  stick_y     = 0.0f;
+	bool   primary     = false; // X on the left controller, A on the right one.
+	bool   secondary   = false; // Y on the left controller, B on the right one.
+	bool   stick_click = false;
+	bool   menu        = false;
+};
+
+// Latest head pose; not valid, at the origin, while no headset session tracks the head.
+[[nodiscard]] VrPose OpenXrGetHeadPose();
+
+// Latest state of the left (0) or right (1) controller. While it is not connected the caller keeps
+// using the keyboard or gamepad.
+[[nodiscard]] VrControllerInput OpenXrGetController(int hand);
+
+} // namespace Libs::Vr
+
+#endif // EMULATOR_SRC_GRAPHICS_PRESENTATION_VRINPUT_H_