ARKit for Godot 3.2

This PR introduces support for ARKit to the iOS version of Godot.
ARKit is Apples Augmented Reality platform.
This PR brings in support for ARKit 1.0 and implements a few ARKit 2.0 features.
It requires iOS 11 to run but should not prevent Godot from running on older versions as long as ARKit remains unused.

modules/arkit/SCsub

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+#!/usr/bin/env python
+
+Import('env')
+Import('env_modules')
+
+env_arkit = env_modules.Clone()
+
+# Add source files
+env_arkit.add_source_files(env.modules_sources, "*.cpp")
+env_arkit.add_source_files(env.modules_sources, "*.mm")

modules/arkit/arkit_interface.h

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+/*************************************************************************/
+/*  arkit_interface.h                                                    */
+/*************************************************************************/
+/*                       This file is part of:                           */
+/*                           GODOT ENGINE                                */
+/*                    http://www.godotengine.org                         */
+/*************************************************************************/
+/* Copyright (c) 2007-2017 Juan Linietsky, Ariel Manzur.                 */
+/* Copyright (c) 2014-2017 Godot Engine contributors (cf. AUTHORS.md)    */
+/*                                                                       */
+/* Permission is hereby granted, free of charge, to any person obtaining */
+/* a copy of this software and associated documentation files (the       */
+/* "Software"), to deal in the Software without restriction, including   */
+/* without limitation the rights to use, copy, modify, merge, publish,   */
+/* distribute, sublicense, and/or sell copies of the Software, and to    */
+/* permit persons to whom the Software is furnished to do so, subject to */
+/* the following conditions:                                             */
+/*                                                                       */
+/* The above copyright notice and this permission notice shall be        */
+/* included in all copies or substantial portions of the Software.       */
+/*                                                                       */
+/* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,       */
+/* EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF    */
+/* MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.*/
+/* IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY  */
+/* CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,  */
+/* TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE     */
+/* SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.                */
+/*************************************************************************/
+
+#ifndef ARKIT_INTERFACE_H
+#define ARKIT_INTERFACE_H
+
+#include "servers/arvr/arvr_interface.h"
+#include "servers/arvr/arvr_positional_tracker.h"
+#include "servers/camera/camera_feed.h"
+
+/**
+	@author Bastiaan Olij <mux213@gmail.com>
+
+	ARKit interface between iPhone and Godot
+*/
+
+// forward declaration for some needed objects
+class ARKitShader;
+
+class ARKitInterface : public ARVRInterface {
+	GDCLASS(ARKitInterface, ARVRInterface);
+
+private:
+	bool initialized;
+	bool session_was_started;
+	bool plane_detection_is_enabled;
+	bool light_estimation_is_enabled;
+	real_t ambient_intensity;
+	real_t ambient_color_temperature;
+
+	Transform transform;
+	CameraMatrix projection;
+	float eye_height, z_near, z_far;
+
+	Ref<CameraFeed> feed;
+	int image_width[2];
+	int image_height[2];
+	PoolVector<uint8_t> img_data[2];
+
+	struct anchor_map {
+		ARVRPositionalTracker *tracker;
+		unsigned char uuid[16];
+	};
+
+	///@TODO should use memory map object from Godot?
+	unsigned int num_anchors;
+	unsigned int max_anchors;
+	anchor_map *anchors;
+	ARVRPositionalTracker *get_anchor_for_uuid(const unsigned char *p_uuid);
+	void remove_anchor_for_uuid(const unsigned char *p_uuid);
+	void remove_all_anchors();
+
+protected:
+	static void _bind_methods();
+
+public:
+	void start_session();
+	void stop_session();
+
+	bool get_anchor_detection_is_enabled() const;
+	void set_anchor_detection_is_enabled(bool p_enable);
+	virtual int get_camera_feed_id();
+
+	bool get_light_estimation_is_enabled() const;
+	void set_light_estimation_is_enabled(bool p_enable);
+
+	real_t get_ambient_intensity() const;
+	real_t get_ambient_color_temperature() const;
+
+	/* while Godot has its own raycast logic this takes ARKits camera into account and hits on any ARAnchor */
+	Array raycast(Vector2 p_screen_coord);
+
+	void notification(int p_what);
+
+	virtual StringName get_name() const;
+	virtual int get_capabilities() const;
+
+	virtual bool is_initialized() const;
+	virtual bool initialize();
+	virtual void uninitialize();
+
+	virtual Size2 get_render_targetsize();
+	virtual bool is_stereo();
+	virtual Transform get_transform_for_eye(ARVRInterface::Eyes p_eye, const Transform &p_cam_transform);
+	virtual CameraMatrix get_projection_for_eye(ARVRInterface::Eyes p_eye, real_t p_aspect, real_t p_z_near, real_t p_z_far);
+	virtual void commit_for_eye(ARVRInterface::Eyes p_eye, RID p_render_target, const Rect2 &p_screen_rect);
+
+	virtual void process();
+
+	// called by delegate (void * because C++ and Obj-C don't always mix, should really change all platform/iphone/*.cpp files to .mm)
+	void _add_or_update_anchor(void *p_anchor);
+	void _remove_anchor(void *p_anchor);
+
+	ARKitInterface();
+	~ARKitInterface();
+};
+
+#endif /* !ARKIT_INTERFACE_H */