nightshade 0.13.3

A cross-platform data-oriented game engine.
Documentation
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use super::frame::XrFrameContext;
use super::input::XrInput;
use ash::vk::{self, Handle};
use openxr as xr;
use std::ffi::{CString, c_void};

const VK_TARGET_VERSION: xr::Version = xr::Version::new(1, 1, 0);
const VK_TARGET_VERSION_ASH: u32 = vk::make_api_version(
    0,
    VK_TARGET_VERSION.major() as u32,
    VK_TARGET_VERSION.minor() as u32,
    VK_TARGET_VERSION.patch(),
);

pub struct XrContext {
    _vk_entry: ash::Entry,
    _vk_instance: ash::Instance,
    instance: xr::Instance,
    _system: xr::SystemId,
    session: xr::Session<xr::Vulkan>,
    frame_wait: xr::FrameWaiter,
    frame_stream: xr::FrameStream<xr::Vulkan>,
    stage: xr::Space,
    swapchain: xr::Swapchain<xr::Vulkan>,
    swapchain_buffers: Vec<wgpu::Texture>,
    resolution: (u32, u32),
    _views: Vec<xr::ViewConfigurationView>,
    action_set: xr::ActionSet,
    move_action: xr::Action<xr::Vector2f>,
    turn_action: xr::Action<xr::Vector2f>,
    _left_hand_action: xr::Action<xr::Posef>,
    _right_hand_action: xr::Action<xr::Posef>,
    left_trigger_action: xr::Action<f32>,
    right_trigger_action: xr::Action<f32>,
    left_grip_action: xr::Action<f32>,
    right_grip_action: xr::Action<f32>,
    a_button_action: xr::Action<bool>,
    b_button_action: xr::Action<bool>,
    left_thumbstick_click_action: xr::Action<bool>,
    left_hand_space: xr::Space,
    right_hand_space: xr::Space,
    player_position: nalgebra_glm::Vec3,
    player_yaw: f32,
    session_running: bool,
    device: wgpu::Device,
    queue: wgpu::Queue,
}

impl XrContext {
    pub fn new() -> Result<Self, Box<dyn std::error::Error>> {
        let xr_entry = xr::Entry::linked();

        let mut required_extensions = xr::ExtensionSet::default();
        required_extensions.khr_vulkan_enable2 = true;

        let xr_instance = xr_entry.create_instance(
            &xr::ApplicationInfo {
                application_name: "nightshade-xr",
                application_version: 1,
                engine_name: "nightshade",
                engine_version: 1,
                api_version: xr::Version::new(1, 0, 0),
            },
            &required_extensions,
            &[],
        )?;

        let system = xr_instance.system(xr::FormFactor::HEAD_MOUNTED_DISPLAY)?;

        let views = xr_instance.enumerate_view_configuration_views(
            system,
            xr::ViewConfigurationType::PRIMARY_STEREO,
        )?;

        let resolution = (
            views[0].recommended_image_rect_width,
            views[0].recommended_image_rect_height,
        );

        let reqs = xr_instance.graphics_requirements::<xr::Vulkan>(system)?;
        if VK_TARGET_VERSION < reqs.min_api_version_supported
            || VK_TARGET_VERSION.major() > reqs.max_api_version_supported.major()
        {
            return Err(format!(
                "OpenXR runtime requires Vulkan version > {}, < {}.0.0",
                reqs.min_api_version_supported,
                reqs.max_api_version_supported.major() + 1
            )
            .into());
        }

        let vk_entry = unsafe { ash::Entry::load()? };
        let flags = wgpu::InstanceFlags::empty();
        let instance_exts = <wgpu_hal::vulkan::Api as wgpu_hal::Api>::Instance::desired_extensions(
            &vk_entry,
            VK_TARGET_VERSION_ASH,
            flags,
        )?;

        let vk_instance = unsafe {
            let extensions_cchar: Vec<_> = instance_exts.iter().map(|s| s.as_ptr()).collect();

            let app_name = CString::new("nightshade-xr")?;
            let vk_app_info = vk::ApplicationInfo::default()
                .application_name(&app_name)
                .application_version(1)
                .engine_name(&app_name)
                .engine_version(1)
                .api_version(VK_TARGET_VERSION_ASH);

            let get_instance_proc_addr: unsafe extern "system" fn(
                *const c_void,
                *const i8,
            ) -> Option<
                unsafe extern "system" fn(),
            > = std::mem::transmute(vk_entry.static_fn().get_instance_proc_addr);

            let vk_instance = xr_instance
                .create_vulkan_instance(
                    system,
                    get_instance_proc_addr,
                    &vk::InstanceCreateInfo::default()
                        .application_info(&vk_app_info)
                        .enabled_extension_names(&extensions_cchar) as *const _
                        as *const _,
                )?
                .map_err(vk::Result::from_raw)?;

            ash::Instance::load(
                vk_entry.static_fn(),
                vk::Instance::from_raw(vk_instance as _),
            )
        };

        let vk_physical_device = vk::PhysicalDevice::from_raw(unsafe {
            xr_instance.vulkan_graphics_device(system, vk_instance.handle().as_raw() as _)? as _
        });

        let vk_instance_ptr = vk_instance.handle().as_raw() as *const c_void;
        let vk_physical_device_ptr = vk_physical_device.as_raw() as *const c_void;

        let vk_device_properties =
            unsafe { vk_instance.get_physical_device_properties(vk_physical_device) };

        if vk_device_properties.api_version < VK_TARGET_VERSION_ASH {
            return Err("Vulkan physical device doesn't support version 1.1".into());
        }

        let wgpu_vk_instance = unsafe {
            <wgpu_hal::vulkan::Api as wgpu_hal::Api>::Instance::from_raw(
                vk_entry.clone(),
                vk_instance.clone(),
                vk_device_properties.api_version,
                0,
                None,
                instance_exts,
                flags,
                wgpu::MemoryBudgetThresholds::default(),
                false,
                Some(Box::new(|| {})),
            )?
        };

        let wgpu_exposed_adapter = wgpu_vk_instance
            .expose_adapter(vk_physical_device)
            .ok_or("Failed to expose adapter")?;

        let adapter_features = wgpu_exposed_adapter.features;
        let desired_features =
            wgpu::Features::INDIRECT_FIRST_INSTANCE | wgpu::Features::MULTI_DRAW_INDIRECT_COUNT;
        let wgpu_features = adapter_features & desired_features;
        let mut enabled_extensions = wgpu_exposed_adapter
            .adapter
            .required_device_extensions(wgpu_features);
        if !enabled_extensions.contains(&ash::khr::swapchain::NAME) {
            enabled_extensions.push(ash::khr::swapchain::NAME);
        }

        let (wgpu_open_device, vk_device_ptr, queue_family_index) = {
            let extensions_cchar: Vec<_> = enabled_extensions.iter().map(|s| s.as_ptr()).collect();
            let mut enabled_phd_features = wgpu_exposed_adapter
                .adapter
                .physical_device_features(&enabled_extensions, wgpu_features);
            let family_index = 0;
            let queue_priorities = [1.0_f32];
            let family_info = vk::DeviceQueueCreateInfo::default()
                .queue_family_index(family_index)
                .queue_priorities(&queue_priorities);
            let family_infos = [family_info];
            let info = enabled_phd_features
                .add_to_device_create(
                    vk::DeviceCreateInfo::default().queue_create_infos(&family_infos),
                )
                .enabled_extension_names(&extensions_cchar);

            let vk_device = unsafe {
                let get_instance_proc_addr: unsafe extern "system" fn(
                    *const c_void,
                    *const i8,
                ) -> Option<
                    unsafe extern "system" fn(),
                > = std::mem::transmute(vk_entry.static_fn().get_instance_proc_addr);

                let vk_device = xr_instance
                    .create_vulkan_device(
                        system,
                        get_instance_proc_addr,
                        vk_physical_device.as_raw() as _,
                        &info as *const _ as *const _,
                    )?
                    .map_err(vk::Result::from_raw)?;

                ash::Device::load(vk_instance.fp_v1_0(), vk::Device::from_raw(vk_device as _))
            };
            let vk_device_ptr = vk_device.handle().as_raw() as *const c_void;

            let wgpu_open_device = unsafe {
                wgpu_exposed_adapter.adapter.device_from_raw(
                    vk_device,
                    None,
                    &enabled_extensions,
                    wgpu_features,
                    &wgpu::Limits::default(),
                    &wgpu::MemoryHints::Performance,
                    family_info.queue_family_index,
                    0,
                )
            }?;

            (
                wgpu_open_device,
                vk_device_ptr,
                family_info.queue_family_index,
            )
        };

        let wgpu_instance =
            unsafe { wgpu::Instance::from_hal::<wgpu_hal::api::Vulkan>(wgpu_vk_instance) };
        let wgpu_adapter = unsafe { wgpu_instance.create_adapter_from_hal(wgpu_exposed_adapter) };
        let adapter_limits = wgpu_adapter.limits();
        let limits = adapter_limits;
        let (wgpu_device, wgpu_queue) = unsafe {
            wgpu_adapter.create_device_from_hal(
                wgpu_open_device,
                &wgpu::DeviceDescriptor {
                    label: None,
                    required_features: wgpu_features,
                    required_limits: limits,
                    memory_hints: wgpu::MemoryHints::Performance,
                    experimental_features: wgpu::ExperimentalFeatures::disabled(),
                    trace: wgpu::Trace::Off,
                },
            )
        }?;

        let (session, frame_wait, frame_stream) = unsafe {
            xr_instance.create_session::<xr::Vulkan>(
                system,
                &xr::vulkan::SessionCreateInfo {
                    instance: vk_instance_ptr,
                    physical_device: vk_physical_device_ptr,
                    device: vk_device_ptr,
                    queue_family_index,
                    queue_index: 0,
                },
            )
        }?;

        let action_set = xr_instance.create_action_set("gameplay", "Gameplay Actions", 0)?;
        let move_action = action_set.create_action::<xr::Vector2f>("move", "Move", &[])?;
        let turn_action = action_set.create_action::<xr::Vector2f>("turn", "Turn", &[])?;

        let left_hand_action =
            action_set.create_action::<xr::Posef>("left_hand_pose", "Left Hand Pose", &[])?;

        let right_hand_action =
            action_set.create_action::<xr::Posef>("right_hand_pose", "Right Hand Pose", &[])?;

        let left_trigger_action =
            action_set.create_action::<f32>("left_trigger", "Left Trigger", &[])?;

        let right_trigger_action =
            action_set.create_action::<f32>("right_trigger", "Right Trigger", &[])?;

        let left_grip_action = action_set.create_action::<f32>("left_grip", "Left Grip", &[])?;

        let right_grip_action = action_set.create_action::<f32>("right_grip", "Right Grip", &[])?;

        let a_button_action = action_set.create_action::<bool>("a_button", "A Button", &[])?;

        let b_button_action = action_set.create_action::<bool>("b_button", "B Button", &[])?;

        let left_thumbstick_click_action = action_set.create_action::<bool>(
            "left_thumbstick_click",
            "Left Thumbstick Click",
            &[],
        )?;

        xr_instance.suggest_interaction_profile_bindings(
            xr_instance.string_to_path("/interaction_profiles/oculus/touch_controller")?,
            &[
                xr::Binding::new(
                    &move_action,
                    xr_instance.string_to_path("/user/hand/left/input/thumbstick")?,
                ),
                xr::Binding::new(
                    &turn_action,
                    xr_instance.string_to_path("/user/hand/right/input/thumbstick")?,
                ),
                xr::Binding::new(
                    &left_hand_action,
                    xr_instance.string_to_path("/user/hand/left/input/grip/pose")?,
                ),
                xr::Binding::new(
                    &right_hand_action,
                    xr_instance.string_to_path("/user/hand/right/input/grip/pose")?,
                ),
                xr::Binding::new(
                    &left_trigger_action,
                    xr_instance.string_to_path("/user/hand/left/input/trigger/value")?,
                ),
                xr::Binding::new(
                    &right_trigger_action,
                    xr_instance.string_to_path("/user/hand/right/input/trigger/value")?,
                ),
                xr::Binding::new(
                    &left_grip_action,
                    xr_instance.string_to_path("/user/hand/left/input/squeeze/value")?,
                ),
                xr::Binding::new(
                    &right_grip_action,
                    xr_instance.string_to_path("/user/hand/right/input/squeeze/value")?,
                ),
                xr::Binding::new(
                    &a_button_action,
                    xr_instance.string_to_path("/user/hand/right/input/a/click")?,
                ),
                xr::Binding::new(
                    &b_button_action,
                    xr_instance.string_to_path("/user/hand/right/input/b/click")?,
                ),
                xr::Binding::new(
                    &left_thumbstick_click_action,
                    xr_instance.string_to_path("/user/hand/left/input/thumbstick/click")?,
                ),
            ],
        )?;

        session.attach_action_sets(&[&action_set])?;

        let left_hand_space =
            left_hand_action.create_space(&session, xr::Path::NULL, xr::Posef::IDENTITY)?;

        let right_hand_space =
            right_hand_action.create_space(&session, xr::Path::NULL, xr::Posef::IDENTITY)?;

        let stage =
            session.create_reference_space(xr::ReferenceSpaceType::STAGE, xr::Posef::IDENTITY)?;

        let swapchain = session.create_swapchain(&xr::SwapchainCreateInfo {
            create_flags: xr::SwapchainCreateFlags::EMPTY,
            usage_flags: xr::SwapchainUsageFlags::COLOR_ATTACHMENT
                | xr::SwapchainUsageFlags::SAMPLED,
            format: vk::Format::R8G8B8A8_SRGB.as_raw() as _,
            sample_count: 1,
            width: resolution.0,
            height: resolution.1,
            face_count: 1,
            array_size: 2,
            mip_count: 1,
        })?;

        let swapchain_images = swapchain.enumerate_images()?;
        let swapchain_buffers: Vec<wgpu::Texture> = swapchain_images
            .into_iter()
            .map(|color_image| {
                let color_image = vk::Image::from_raw(color_image);
                let wgpu_hal_texture = unsafe {
                    let hal_dev = wgpu_device
                        .as_hal::<wgpu_hal::vulkan::Api>()
                        .ok_or("Failed to get HAL device")?;
                    hal_dev.texture_from_raw(
                        color_image,
                        &wgpu_hal::TextureDescriptor {
                            label: Some("VR Swapchain"),
                            size: wgpu::Extent3d {
                                width: resolution.0,
                                height: resolution.1,
                                depth_or_array_layers: 2,
                            },
                            mip_level_count: 1,
                            sample_count: 1,
                            dimension: wgpu::TextureDimension::D2,
                            format: wgpu::TextureFormat::Rgba8UnormSrgb,
                            usage: wgpu::TextureUses::COLOR_TARGET | wgpu::TextureUses::COPY_DST,
                            memory_flags: wgpu_hal::MemoryFlags::empty(),
                            view_formats: vec![],
                        },
                        None,
                        wgpu_hal::vulkan::TextureMemory::External,
                    )
                };
                let texture = unsafe {
                    wgpu_device.create_texture_from_hal::<wgpu_hal::vulkan::Api>(
                        wgpu_hal_texture,
                        &wgpu::TextureDescriptor {
                            label: Some("VR Swapchain"),
                            size: wgpu::Extent3d {
                                width: resolution.0,
                                height: resolution.1,
                                depth_or_array_layers: 2,
                            },
                            mip_level_count: 1,
                            sample_count: 1,
                            dimension: wgpu::TextureDimension::D2,
                            format: wgpu::TextureFormat::Rgba8UnormSrgb,
                            usage: wgpu::TextureUsages::RENDER_ATTACHMENT
                                | wgpu::TextureUsages::COPY_DST,
                            view_formats: &[],
                        },
                    )
                };
                Ok(texture)
            })
            .collect::<Result<Vec<_>, Box<dyn std::error::Error>>>()?;

        tracing::info!(
            "OpenXR session created successfully with resolution {}x{}",
            resolution.0,
            resolution.1
        );

        Ok(Self {
            _vk_entry: vk_entry,
            _vk_instance: vk_instance,
            instance: xr_instance,
            _system: system,
            session,
            frame_wait,
            frame_stream,
            stage,
            swapchain,
            swapchain_buffers,
            resolution,
            _views: views,
            action_set,
            move_action,
            turn_action,
            _left_hand_action: left_hand_action,
            _right_hand_action: right_hand_action,
            left_trigger_action,
            right_trigger_action,
            left_grip_action,
            right_grip_action,
            a_button_action,
            b_button_action,
            left_thumbstick_click_action,
            left_hand_space,
            right_hand_space,
            player_position: nalgebra_glm::vec3(0.0, 0.0, 0.0),
            player_yaw: 0.0,
            session_running: false,
            device: wgpu_device,
            queue: wgpu_queue,
        })
    }

    pub fn device(&self) -> &wgpu::Device {
        &self.device
    }

    pub fn queue(&self) -> &wgpu::Queue {
        &self.queue
    }

    pub fn resolution(&self) -> (u32, u32) {
        self.resolution
    }

    pub fn surface_format(&self) -> wgpu::TextureFormat {
        wgpu::TextureFormat::Rgba8UnormSrgb
    }

    pub fn set_player_yaw(&mut self, yaw: f32) {
        self.player_yaw = yaw;
    }

    pub fn set_player_position(&mut self, position: nalgebra_glm::Vec3) {
        self.player_position = position;
    }

    pub fn poll_events(&mut self) -> Result<bool, Box<dyn std::error::Error>> {
        let mut event_buffer = xr::EventDataBuffer::new();
        while let Some(event) = self.instance.poll_event(&mut event_buffer)? {
            match event {
                xr::Event::SessionStateChanged(state_change) => {
                    tracing::info!("XR Session state changed to: {:?}", state_change.state());
                    match state_change.state() {
                        xr::SessionState::READY => {
                            self.session
                                .begin(xr::ViewConfigurationType::PRIMARY_STEREO)?;
                            self.session_running = true;
                            tracing::info!("XR Session started");
                        }
                        xr::SessionState::STOPPING => {
                            self.session.end()?;
                            self.session_running = false;
                            tracing::info!("XR Session ended");
                        }
                        xr::SessionState::EXITING | xr::SessionState::LOSS_PENDING => {
                            tracing::info!("XR Session exiting");
                            return Ok(false);
                        }
                        _ => {}
                    }
                }
                xr::Event::InstanceLossPending(_) => {
                    tracing::info!("XR Instance loss pending");
                    return Ok(false);
                }
                _ => {}
            }
        }
        Ok(true)
    }

    pub fn wait_frame(&mut self) -> Result<Option<xr::FrameState>, Box<dyn std::error::Error>> {
        if !self.session_running {
            return Ok(None);
        }
        Ok(Some(self.frame_wait.wait()?))
    }

    pub fn update_input(
        &mut self,
        delta_time: f32,
        predicted_display_time: xr::Time,
        locomotion_enabled: bool,
        locomotion_speed: f32,
    ) -> Result<XrInput, Box<dyn std::error::Error>> {
        self.session.sync_actions(&[(&self.action_set).into()])?;

        let move_state = self.move_action.state(&self.session, xr::Path::NULL)?;
        let turn_state = self.turn_action.state(&self.session, xr::Path::NULL)?;

        let (_, views) = self.session.locate_views(
            xr::ViewConfigurationType::PRIMARY_STEREO,
            predicted_display_time,
            &self.stage,
        )?;

        let (head_yaw, openxr_quat, head_pose_position) = if !views.is_empty() {
            let head_pose = &views[0].pose;
            let quat = nalgebra_glm::quat(
                head_pose.orientation.w,
                head_pose.orientation.z,
                head_pose.orientation.y,
                head_pose.orientation.x,
            );
            let head_forward =
                nalgebra_glm::quat_rotate_vec3(&quat, &nalgebra_glm::vec3(0.0, 0.0, -1.0));
            let yaw = (-head_forward.x).atan2(-head_forward.z);
            (yaw, Some(quat), Some(head_pose.position))
        } else {
            (0.0, None, None)
        };

        if turn_state.current_state.x.abs() > 0.1 {
            let turn_speed = 2.0;
            self.player_yaw -= turn_state.current_state.x * turn_speed * delta_time;
        }

        if locomotion_enabled {
            let move_speed = if locomotion_speed > 0.0 {
                locomotion_speed
            } else {
                2.0
            };

            if move_state.current_state.x.abs() > 0.1 || move_state.current_state.y.abs() > 0.1 {
                let combined_yaw = head_yaw + self.player_yaw;

                let move_x = move_state.current_state.x;
                let move_z = -move_state.current_state.y;

                let rotated_x = move_x * combined_yaw.cos() - move_z * combined_yaw.sin();
                let rotated_z = move_x * combined_yaw.sin() + move_z * combined_yaw.cos();

                self.player_position.x += rotated_x * move_speed * delta_time;
                self.player_position.z += rotated_z * move_speed * delta_time;
            }

            let left_trigger_value = self
                .left_trigger_action
                .state(&self.session, xr::Path::NULL)
                .map(|s| s.current_state)
                .unwrap_or(0.0);
            let right_trigger_value = self
                .right_trigger_action
                .state(&self.session, xr::Path::NULL)
                .map(|s| s.current_state)
                .unwrap_or(0.0);

            let vertical_input = right_trigger_value - left_trigger_value;
            if vertical_input.abs() > 0.1 {
                self.player_position.y += vertical_input * move_speed * delta_time;
            }
        }

        let (head_position, head_orientation) = if let (Some(quat), Some(pos)) =
            (openxr_quat, head_pose_position)
        {
            let local_x = -pos.x;
            let local_z = -pos.z;
            let rotated_x = local_x * self.player_yaw.cos() + local_z * self.player_yaw.sin();
            let rotated_z = -local_x * self.player_yaw.sin() + local_z * self.player_yaw.cos();
            let world_head_pos =
                self.player_position + nalgebra_glm::vec3(rotated_x, pos.y, rotated_z);

            let player_rotation =
                nalgebra_glm::quat_angle_axis(self.player_yaw, &nalgebra_glm::vec3(0.0, 1.0, 0.0));
            let flip_x = nalgebra_glm::quat_angle_axis(
                std::f32::consts::PI,
                &nalgebra_glm::vec3(1.0, 0.0, 0.0),
            );
            let world_head_orientation = player_rotation * flip_x * quat;

            (world_head_pos, world_head_orientation)
        } else {
            (self.player_position, nalgebra_glm::quat_identity())
        };

        let left_trigger = self
            .left_trigger_action
            .state(&self.session, xr::Path::NULL)
            .map(|s| s.current_state)
            .unwrap_or(0.0);

        let right_trigger = self
            .right_trigger_action
            .state(&self.session, xr::Path::NULL)
            .map(|s| s.current_state)
            .unwrap_or(0.0);

        let left_grip = self
            .left_grip_action
            .state(&self.session, xr::Path::NULL)
            .map(|s| s.current_state)
            .unwrap_or(0.0);

        let right_grip = self
            .right_grip_action
            .state(&self.session, xr::Path::NULL)
            .map(|s| s.current_state)
            .unwrap_or(0.0);

        let a_button = self
            .a_button_action
            .state(&self.session, xr::Path::NULL)
            .map(|s| s.current_state)
            .unwrap_or(false);

        let b_button = self
            .b_button_action
            .state(&self.session, xr::Path::NULL)
            .map(|s| s.current_state)
            .unwrap_or(false);

        let left_thumbstick_click = self
            .left_thumbstick_click_action
            .state(&self.session, xr::Path::NULL)
            .map(|s| s.current_state)
            .unwrap_or(false);

        let left_hand_pose = self
            .left_hand_space
            .locate(&self.stage, predicted_display_time)
            .ok()
            .filter(|loc| {
                loc.location_flags.contains(
                    xr::SpaceLocationFlags::POSITION_VALID
                        | xr::SpaceLocationFlags::ORIENTATION_VALID,
                )
            })
            .map(|loc| loc.pose);

        let right_hand_pose = self
            .right_hand_space
            .locate(&self.stage, predicted_display_time)
            .ok()
            .filter(|loc| {
                loc.location_flags.contains(
                    xr::SpaceLocationFlags::POSITION_VALID
                        | xr::SpaceLocationFlags::ORIENTATION_VALID,
                )
            })
            .map(|loc| loc.pose);

        Ok(XrInput {
            thumbstick: nalgebra_glm::vec2(move_state.current_state.x, move_state.current_state.y),
            right_thumbstick: nalgebra_glm::vec2(
                turn_state.current_state.x,
                turn_state.current_state.y,
            ),
            left_trigger,
            right_trigger,
            left_grip,
            right_grip,
            a_button,
            b_button,
            left_thumbstick_click,
            left_hand_pose,
            right_hand_pose,
            player_position: self.player_position,
            player_yaw: self.player_yaw,
            head_yaw,
            head_position,
            head_orientation,
        })
    }

    pub fn begin_frame(&mut self) -> Result<Option<XrFrameContext>, Box<dyn std::error::Error>> {
        let Some(frame_state) = self.wait_frame()? else {
            return Ok(None);
        };

        self.frame_stream.begin()?;

        if !frame_state.should_render {
            self.frame_stream.end(
                frame_state.predicted_display_time,
                xr::EnvironmentBlendMode::OPAQUE,
                &[],
            )?;
            return Ok(None);
        }

        let (view_state_flags, views) = self.session.locate_views(
            xr::ViewConfigurationType::PRIMARY_STEREO,
            frame_state.predicted_display_time,
            &self.stage,
        )?;

        if !view_state_flags
            .contains(xr::ViewStateFlags::POSITION_VALID | xr::ViewStateFlags::ORIENTATION_VALID)
        {
            self.frame_stream.end(
                frame_state.predicted_display_time,
                xr::EnvironmentBlendMode::OPAQUE,
                &[],
            )?;
            return Ok(None);
        }

        let image_index = self.swapchain.acquire_image()?;
        self.swapchain.wait_image(xr::Duration::INFINITE)?;

        Ok(Some(XrFrameContext {
            frame_state,
            views,
            image_index,
            player_position: self.player_position,
            player_yaw: self.player_yaw,
        }))
    }

    pub fn get_eye_texture_view(
        &self,
        frame_ctx: &XrFrameContext,
        eye_index: usize,
    ) -> wgpu::TextureView {
        let swapchain_texture = &self.swapchain_buffers[frame_ctx.image_index as usize];
        swapchain_texture.create_view(&wgpu::TextureViewDescriptor {
            label: Some(&format!("XR Eye {}", eye_index)),
            format: Some(wgpu::TextureFormat::Rgba8UnormSrgb),
            dimension: Some(wgpu::TextureViewDimension::D2),
            aspect: wgpu::TextureAspect::All,
            base_mip_level: 0,
            mip_level_count: None,
            base_array_layer: eye_index as u32,
            array_layer_count: Some(1),
            usage: None,
        })
    }

    pub fn end_frame(
        &mut self,
        frame_ctx: XrFrameContext,
    ) -> Result<(), Box<dyn std::error::Error>> {
        self.swapchain.release_image()?;

        let rect = xr::Rect2Di {
            offset: xr::Offset2Di { x: 0, y: 0 },
            extent: xr::Extent2Di {
                width: self.resolution.0 as i32,
                height: self.resolution.1 as i32,
            },
        };

        let sub_images: Vec<_> = frame_ctx
            .views
            .iter()
            .enumerate()
            .map(|(view_index, view)| {
                xr::CompositionLayerProjectionView::new()
                    .pose(view.pose)
                    .fov(view.fov)
                    .sub_image(
                        xr::SwapchainSubImage::new()
                            .swapchain(&self.swapchain)
                            .image_array_index(view_index as u32)
                            .image_rect(rect),
                    )
            })
            .collect();

        let projection_layer = xr::CompositionLayerProjection::new()
            .space(&self.stage)
            .views(&sub_images);

        self.frame_stream.end(
            frame_ctx.frame_state.predicted_display_time,
            xr::EnvironmentBlendMode::OPAQUE,
            &[&projection_layer],
        )?;

        Ok(())
    }
}