move some modules into a new graphics submodule

Force-Push: yes
Change-Id: I5cbdf59870258f099fc6dd47ff2f1566376c1585

1 files changed, 842 insertions, 0 deletions

diff --git a/src/graphics/permanent.rs b/src/graphics/permanent.rs
new file mode 100644
index 0000000..5282e21
--- /dev/null
+++ b/src/graphics/permanent.rs
@@ -0,0 +1,842 @@
+#![deny(unsafe_code)]
+use crate::error::*;
+
+use std::collections::{ BTreeMap, BTreeSet, HashSet };
+use std::ffi::{ c_void, CStr };
+use vulkanalia::{ Device, Entry, Instance, Version };
+use vulkanalia::bytecode::Bytecode;
+use vulkanalia::loader::{ LibloadingLoader, LIBRARY };
+use vulkanalia::vk::{ self, HasBuilder,
+                      ApplicationInfo, InstanceCreateInfo,
+                      DeviceV1_0, EntryV1_0, InstanceV1_0,
+                      ExtDebugUtilsExtensionInstanceCommands,
+                      KhrSurfaceExtensionInstanceCommands };
+use winit::dpi::LogicalSize;
+use winit::event_loop::ActiveEventLoop;
+use winit::window::{ Window, WindowAttributes };
+
+
+const VULKAN_FIRST_PORTABILITY_VERSION: Version = Version::new(1, 3, 216);
+
+
+//   The PermanentGraphicsState collects the various windowing-system and
+// Vulkan objects which never need to be regenerated once they're created. The
+// ones which do need that are collected below, in WindowDressing.
+pub struct PermanentGraphicsState {
+  //   The "window" is the usual operating-system concept of a window; it's
+  // provided by winit, and may be X11, Wayland, or some more curious thing.
+  // The way we initialize Vulkan requires us to have at least one of these;
+  // we could have more, but for now, we don't.
+  pub window: Window,
+
+  //   The Vulkan "entry" is the part of the Vulkan library ecosystem that's
+  // responsible for finding and loading the other parts. Once we have the
+  // instance, the entry is never directly used again, but we retain it
+  // because doing otherwise would segfault.
+  #[allow(unused)]
+  entry: Entry,
+
+  //   The Vulkan "instance" is the bulk of the Vulkan library, with most of
+  // the high-level responsibilities around lifecycle management.
+  pub instance: Instance,
+
+  //   The debug messager is a Vulkan object representing our callback which
+  // Vulkan uses to tell us things.
+  //
+  //   Vulkan spells "messager" as "messenger", but this is absurd
+  // over-formality and we don't indulge it.
+  //
+  //    Once we've created this, we never actually need to do anything with
+  // it, but we do need to retain it, so here it is.
+  debug_messager: Option<vk::DebugUtilsMessengerEXT>,
+
+  //   The Vulkan "surface" is the destination that rendering happens into.
+  // It is connected to the window but distinct from it. Since we always have
+  // exactly one window, this is permanent state.
+  pub surface: vk::SurfaceKHR,
+
+  //   The Vulkan "device" is the abstraction for a GPU. A physical one is the
+  // actual GPU, and a logical one is our connection to it. We pick a physical
+  // device during initialization, but only the logical one is used later, so
+  // it's all we track. We'll be referencing the logical device a lot, so we
+  // follow Vulkan's lead and let it have a short variable name.
+  pub device: Device,
+
+  //   Vulkan has a first-class concept of command queues. We have two of
+  // them, one for graphics drawing commands and one for presentation.
+  //
+  //   While these are often the same queue, there is no guarantee of that;
+  // sometimes there's no queue family that supports both operations together.
+  // For simplicity's sake we treat them as if they're separate, though the
+  // handles will alias each other when the initialization logic was able to
+  // find a family that does both.
+  //
+  //   Yes, this means the compiler has to deal with pointer aliasing
+  // concerns, which have a tendency to defeat optimizations. Alas.
+  pub graphics_queue: vk::Queue,
+  pub presentation_queue: vk::Queue,
+}
+
+
+#[derive(Debug)]
+pub struct QueueFamilyIndices {
+  pub graphics: u32,
+  pub presentation: u32,
+}
+
+//   These structs exist for use in function calling, to remove the potential
+// for accidentally passing or returning one boolean as if it's another.
+struct EnablePortability(bool);
+struct EnableValidation(bool);
+pub struct EnableAnisotropy(pub bool);
+pub struct EnableSwapchain(pub bool);
+
+
+impl PermanentGraphicsState {
+  #[allow(unsafe_code)]
+  pub fn new(event_loop: &ActiveEventLoop)
+      -> Result<(Self, GraphicsStateForReinit, EnableAnisotropy,
+                 EnableSwapchain)>
+  {
+    let window = init_window(event_loop)?;
+
+    //   There are a few Vulkan features (in the informal sense of
+    // "feature") that we want to be able to run both with and without.
+    // The enable_* values, here and below, are wrapped booleans that describe
+    // those choices.
+    //
+    //   These are only used to communicate between initialization
+    // phases; we don't keep them around after that.
+    let (entry, instance, debug_messager,
+         enable_portability, enable_validation)
+        = init_vulkan(&window)?;
+
+    //   Conveniently, Vulkanalia's "window" feature allows it to get the
+    // platform-specific stuff directly out of winit for us. This wrapper does
+    // not correspond 1:1 to a Vulkan function; rather, it picks the Vulkan
+    // function from the appropriate platform-specific extension.
+    //
+    //   The reason it takes the window twice is that that first one is
+    // actually there to reference the display (in the x11 sense of "display"
+    // meaning the connection to the windowing system).
+    let surface = unsafe {
+      vulkanalia::window::create_surface(&instance, &window, &window)
+    }?;
+
+    let (physical_device, device, indices, sample_count, graphics_queue,
+         presentation_queue, enable_anisotropy, enable_swapchain)
+        = init_vulkan_device(&instance, &surface,
+                             enable_validation, enable_portability)?;
+
+    let descriptor_set_layout = init_descriptor_set_layout(&device)?;
+
+    Ok((PermanentGraphicsState {
+      window, entry, instance, debug_messager, surface, device,
+      graphics_queue, presentation_queue
+    }, GraphicsStateForReinit {
+      physical_device, indices, sample_count, descriptor_set_layout,
+    }, enable_anisotropy, enable_swapchain))
+  }
+
+  #[allow(unsafe_code)]
+  pub fn destroy(self) -> () {
+    unsafe { self.device.destroy_device(None) };
+
+    unsafe { self.instance.destroy_surface_khr(self.surface, None) };
+
+    //   Everything but the instance itself should already be destroyed,
+    // before we destroy the debug messager. The special hook to get debug
+    // messages while destroying the instance itself only applies to the
+    // instance and the messager, so if we were to destroy anything we
+    // shouldn't after this point, we'd miss out on diagnostics.
+    if let Some(debug_messager) = self.debug_messager {
+      unsafe {
+        self.instance.destroy_debug_utils_messenger_ext(debug_messager, None);
+      }
+    }
+
+    unsafe { self.instance.destroy_instance(None) };
+  }
+
+  //   We expect our caller to have already verified that the device supports
+  // the swapchain extension.
+  #[allow(unsafe_code)]
+  pub fn find_device_swapchain_features(instance: &Instance,
+                                        surface: &vk::SurfaceKHR,
+                                        physical_device: &vk::PhysicalDevice)
+      -> Result<Acceptable<(vk::SurfaceCapabilitiesKHR,
+                            Vec<vk::SurfaceFormatKHR>,
+                            Vec<vk::PresentModeKHR>)>>
+  {
+    let capabilities = unsafe {
+      instance.get_physical_device_surface_capabilities_khr(
+          *physical_device, *surface)
+    }?;
+    let formats = unsafe {
+      instance.get_physical_device_surface_formats_khr(
+          *physical_device, *surface)
+    }?;
+    let presentation_modes = unsafe {
+      instance.get_physical_device_surface_present_modes_khr(
+          *physical_device, *surface)
+    }?;
+
+    if formats.is_empty() {
+      Ok(Acceptable::Rejected("No matching surface formats.".to_string()))
+    } else if presentation_modes.is_empty() {
+      Ok(Acceptable::Rejected("No matching presentation modes.".to_string()))
+    } else {
+      Ok(Acceptable::Accepted((capabilities, formats, presentation_modes)))
+    }
+  }
+
+
+  #[allow(unsafe_code)]
+  pub fn load_spirv_shader_module(device: &Device, binary: &[u8])
+      -> Result<vk::ShaderModule>
+  {
+    let bytecode = Bytecode::new(binary)?;
+
+    let module_info = vk::ShaderModuleCreateInfo::builder()
+                          .code(bytecode.code())
+                          .code_size(bytecode.code_size());
+
+    let module = unsafe {
+      device.create_shader_module(&module_info, None)
+    }?;
+
+    Ok(module)
+  }
+}
+
+
+//   The GraphicsStateForReinit connects Vulkan objects which are only needed
+// during the creation of the window-dressing objects. They are used during
+// initial startup, and again any time the window-dressing needs to be
+// reinitialized. Most notably, they are not needed when rendering.
+pub struct GraphicsStateForReinit {
+  pub physical_device: vk::PhysicalDevice,
+  pub indices: QueueFamilyIndices,
+  pub sample_count: vk::SampleCountFlags,
+  pub descriptor_set_layout: vk::DescriptorSetLayout,
+}
+
+
+impl GraphicsStateForReinit {
+  #[allow(unsafe_code)]
+  pub fn destroy(self, device: &Device) -> () {
+    unsafe {
+      device.destroy_descriptor_set_layout(self.descriptor_set_layout, None)
+    };
+  }
+}
+
+
+fn init_window(event_loop: &ActiveEventLoop) -> Result<Window> {
+  //   Notice that we do this before having a Vulkan instance. The window is
+  // actually a parameter needed to create the instance; see
+  // init_vulkan(), below.
+  let window_attributes = WindowAttributes::default()
+          .with_title("Love, Curiosity, Justice")
+          .with_inner_size(LogicalSize::new(1024, 768));
+
+  Ok(event_loop.create_window(window_attributes)?)
+}
+
+
+#[allow(unsafe_code)]
+fn init_vulkan(window: &Window)
+    -> Result<(Entry, Instance, Option<vk::DebugUtilsMessengerEXT>,
+               EnablePortability, EnableValidation)>
+{
+  let enable_validation = cfg!(feature = "vulkan-validation")
+                          || cfg!(debug_assertions);
+
+  //   Okay, so, a Vulkan "entry" is a small set of functions which are used
+  // to dynamically load all the rest of Vulkan. It's our responsibility to
+  // know how to load the entry, then it will take care of the rest. At
+  // least, that's the theory, but also see flake.nix for all the
+  // FHS-centric assumptions it makes that we have to correct.
+  //
+  //   Anyway, Vulkanalia offers an integration with libloading, which is a
+  // crate that wraps POSIX dlopen(). We use that; it's enabled by
+  // Vulkanalia's "libloading" feature.
+  let loader = unsafe { LibloadingLoader::new(LIBRARY) }?;
+  let entry = unsafe { Entry::new(loader) }?;
+
+  //   Since there's a lot of factors going into our instance creation
+  // request, we'll build up the parameters mutably.
+  let mut flags = vk::InstanceCreateFlags::empty();
+  let mut extensions = Vec::new();
+  let mut layers = Vec::new();
+
+  //   Before we go any further, use Vulkan's introspection to list off
+  // what's available.
+  let mut available_extensions = HashSet::new();
+  for extension in
+          unsafe { entry.enumerate_instance_extension_properties(None) }?
+  {
+    available_extensions.insert(extension.extension_name);
+  }
+  let available_extensions = available_extensions;
+
+  let mut available_layers = HashSet::new();
+  for layer in unsafe { entry.enumerate_instance_layer_properties() }? {
+    available_layers.insert(layer.layer_name);
+  }
+  let available_layers = available_layers;
+
+  //   There are certain extensions which are required by the nature of our
+  // windowing system. Happily, vulanaklia knows how to deal with that based
+  // on the type of window we give it.
+  //
+  //   This is possible because of an integration between Vulkanalia and
+  // winit, which is enabled by Vulkanalia's "window" feature.
+  for extension in vulkanalia::window::get_required_instance_extensions(
+                       window)
+  {
+    extensions.push(extension.as_ptr());
+  }
+
+  //   Deal with Vulkan's thing about opting in to non-conforming
+  // implementations.
+  let enable_portability = if entry.version()?
+                              >= VULKAN_FIRST_PORTABILITY_VERSION
+  {
+    if cfg!(target_os = "macos") {
+      // Vulkan on the Mac is not fully conforming.
+      extensions.push(
+          vk::KHR_GET_PHYSICAL_DEVICE_PROPERTIES2_EXTENSION.name.as_ptr());
+      extensions.push(
+          vk::KHR_PORTABILITY_ENUMERATION_EXTENSION.name.as_ptr());
+      flags.insert(vk::InstanceCreateFlags::ENUMERATE_PORTABILITY_KHR);
+
+      EnablePortability(true)
+    } else {
+      EnablePortability(false)
+    }
+  } else {
+    EnablePortability(false)
+  };
+
+  // Request the LunarG validation layer, when appropriate.
+  let validation_layer_name = vk::ExtensionName::from_bytes(
+                                  b"VK_LAYER_KHRONOS_validation");
+  let enable_validation = if enable_validation {
+    if available_layers.contains(&validation_layer_name) {
+      layers.push(validation_layer_name.as_ptr());
+
+      EnableValidation(true)
+    } else {
+      eprintln!("Vulkan validation requested at build time, \
+                 but no validation layer available.");
+
+      EnableValidation(false)
+    }
+  } else {
+    EnableValidation(false)
+  };
+
+  //   Request the debug extension. This is the first of three bits of code
+  // that deal with this, and has the resonsibility of making sure the
+  // extension is in the list we ask for.
+  let debug_extension_name = vk::EXT_DEBUG_UTILS_EXTENSION.name;
+  if available_extensions.contains(&debug_extension_name) {
+    extensions.push(debug_extension_name.as_ptr());
+  } else {
+    eprintln!("Vulkan debug extension not available; \
+               this may mean other messages don't show up.");
+  }
+
+  let application_info = ApplicationInfo::builder()
+          .application_name(b"Surreality\0")
+          .application_version(vk::make_version(1, 0, 0))
+          .engine_name(b"Surreality\0")
+          .engine_version(vk::make_version(1, 0, 0))
+          .api_version(vk::make_version(1, 0, 0));
+
+  //   Deceptively, this DOES get mutated later, but Vulkanalia doesn't see
+  // it that way.
+  let instance_create_info = InstanceCreateInfo::builder()
+          .application_info(&application_info)
+          .flags(flags)
+          .enabled_extension_names(&extensions)
+          .enabled_layer_names(&layers);
+
+  //   Configure the debug extension. This is the middle of three bits of
+  // code that deal with this, and has the responsibility of making sure
+  // the callback will be available during instance creation and
+  // destruction, which is done in a special way that doesn't rely on having
+  // a messager, since there can't be one for those steps.
+  let debug_info = if available_extensions.contains(&debug_extension_name) {
+    let mut debug_info = vk::DebugUtilsMessengerCreateInfoEXT::builder()
+            .message_severity(vk::DebugUtilsMessageSeverityFlagsEXT::all())
+            .message_type(vk::DebugUtilsMessageTypeFlagsEXT::GENERAL
+                          | vk::DebugUtilsMessageTypeFlagsEXT::VALIDATION
+                          | vk::DebugUtilsMessageTypeFlagsEXT::PERFORMANCE)
+            .user_callback(Some(debug_messager_callback));
+
+    //   Please notice that the reference we pass here will escape Rust's
+    // lifetime checking, since push_next() casts it to a pointer. We don't
+    // get nearly as strong a safety guarantee as one might hope (and as [1]
+    // naively reassures us we do). If we did, the thing we're doing would
+    // actually be forbidden!
+    //
+    // [1] https://kylemayes.github.io/vulkanalia/
+    instance_create_info.push_next(&mut debug_info);
+
+    Some(debug_info)
+  } else { None };
+
+  let instance = unsafe {
+    //   We're promising that every struct referenced here is still alive.
+    // Since it's all pointers, that's... not a thing we statically know. Be
+    // aware. Only you can prevent segfaults.
+    entry.create_instance(&instance_create_info, None)
+  }?;
+
+  //   Configure the debug extension. This is the last of three bits of code
+  // that deal with this, and has the responsibility of asking the instance,
+  // which now exists, to create the debug messager.
+  let debug_messager = if let Some(debug_info) = debug_info {
+    #[allow(unsafe_code)]
+    Some(unsafe {
+      instance.create_debug_utils_messenger_ext(&debug_info, None)
+    }?)
+  } else {
+    None
+  };
+
+  Ok((entry, instance, debug_messager,
+      enable_portability, enable_validation))
+}
+
+
+#[allow(unsafe_code)]
+fn init_vulkan_device(instance: &Instance, surface: &vk::SurfaceKHR,
+                      enable_validation: EnableValidation,
+                      enable_portability: EnablePortability)
+    -> Result<(vk::PhysicalDevice, Device, QueueFamilyIndices,
+               vk::SampleCountFlags, vk::Queue, vk::Queue, EnableAnisotropy,
+               EnableSwapchain)>
+{
+  let (physical_device, indices, sample_count)
+          = pick_vulkan_device(instance, surface)?;
+
+  //   We enumerate the device extensions here so they can inform
+  // configuration. We already did this in score_vulkan_device(), but here
+  // it is again.
+  let mut available_extensions = HashSet::new();
+  for extension in unsafe {
+    instance.enumerate_device_extension_properties(physical_device, None)
+  }? {
+    available_extensions.insert(extension.extension_name);
+  }
+  let available_extensions = available_extensions;
+
+  //   Old versions of Vulkan want layers to be enabled at the device
+  // level as well. Newer ones will ignore this and just use the instance
+  // layers.
+  let available_features = unsafe {
+    instance.get_physical_device_features(physical_device)
+  };
+  let mut features = vk::PhysicalDeviceFeatures::builder();
+  let mut extensions = Vec::new();
+  let mut layers = Vec::new();
+
+  let validation_layer_name = vk::ExtensionName::from_bytes(
+                                  b"VK_LAYER_KHRONOS_validation");
+  if enable_validation.0 {
+    //   It's not concerning if this isn't supported, because device
+    // layers are ignored on recent versions, they're purely historical.
+    if available_extensions.contains(&validation_layer_name) {
+      layers.push(validation_layer_name.as_ptr());
+    }
+  }
+
+  let portability_extension_name = vk::ExtensionName::from_bytes(
+                                       b"VK_KHR_portability_subset");
+  if enable_portability.0 {
+    //   This is untested, since the only scenario where it would come up
+    // is on a Mac, which we don't actually support. Sorry, and good luck.
+    if available_extensions.contains(&portability_extension_name) {
+      extensions.push(portability_extension_name.as_ptr());
+    }
+  }
+
+  let swapchain_extension_name = vk::KHR_SWAPCHAIN_EXTENSION.name;
+  let enable_swapchain = if available_extensions.contains(
+                                &swapchain_extension_name)
+  {
+    //   It's important that we not call the swapchain extension
+    // functions until we've verified the extension is supported. To
+    // emphasize that, we do it on a separate line.
+    //
+    //   We've done this check once already, in scoring, and now here
+    // we are discarding its results a second time. We'll do it for the
+    // third and last time in swapchain creation.
+    if let Acceptable::Accepted(_)
+           = PermanentGraphicsState::find_device_swapchain_features(
+                 &instance, &surface, &physical_device)?
+    {
+      extensions.push(swapchain_extension_name.as_ptr());
+
+      EnableSwapchain(true)
+    } else {
+      EnableSwapchain(false)
+    }
+  } else {
+    EnableSwapchain(false)
+  };
+
+  let enable_anisotropy = if available_features.sampler_anisotropy
+                             == vk::TRUE
+  {
+    features = features.sampler_anisotropy(true);
+
+    EnableAnisotropy(true)
+  } else {
+    EnableAnisotropy(false)
+  };
+
+  //   We have one or more queue family indices; we don't know a priori
+  // how many, because it's possible some of them are the same. We only
+  // want to create one queue per distinct family, so we find the unique
+  // indices...
+  let mut unique_queue_family_indices = BTreeSet::new();
+  unique_queue_family_indices.insert(indices.graphics);
+  unique_queue_family_indices.insert(indices.presentation);
+
+  // ... then add a queue create info struct for each.
+  let mut queues = Vec::new();
+  for index in unique_queue_family_indices {
+    //   Passing the priorities vector also implicitly sets the count of
+    // how many queues we are creating within the family. This nicety is
+    // one of the fun things Vulkanalia's builders do for us.
+    queues.push(vk::DeviceQueueCreateInfo::builder()
+                    .queue_family_index(index)
+                    .queue_priorities(&[1.0]));
+  }
+
+  let device_info = vk::DeviceCreateInfo::builder()
+          .queue_create_infos(&queues)
+          .enabled_layer_names(&layers)
+          .enabled_extension_names(&extensions)
+          .enabled_features(&features);
+
+  let device = unsafe {
+    instance.create_device(physical_device, &device_info, None)
+  }?;
+
+  //   So, this is a little confusing. Queues are found in queue families.
+  // The family has an index within the device, and the queue has an index
+  // within the family. We computed the family index above, and when we
+  // created the device we told it to create just a single queue in that
+  // family. Now we pass both indices to find the actual queue object.
+  let graphics_queue = unsafe {
+    device.get_device_queue(indices.graphics, 0)
+  };
+
+  let presentation_queue = unsafe {
+    device.get_device_queue(indices.presentation, 0)
+  };
+
+  Ok((physical_device, device, indices, sample_count, graphics_queue,
+      presentation_queue, enable_anisotropy, enable_swapchain))
+}
+
+
+#[allow(unsafe_code)]
+fn init_descriptor_set_layout(device: &Device)
+    -> Result<vk::DescriptorSetLayout>
+{
+  let uniform_block_binding = vk::DescriptorSetLayoutBinding::builder()
+          .binding(0)
+          .descriptor_type(vk::DescriptorType::UNIFORM_BUFFER)
+          .descriptor_count(1)
+          .stage_flags(vk::ShaderStageFlags::VERTEX);
+
+  let sampler_binding = vk::DescriptorSetLayoutBinding::builder()
+          .binding(1)
+          .descriptor_type(vk::DescriptorType::COMBINED_IMAGE_SAMPLER)
+          .descriptor_count(1)
+          .stage_flags(vk::ShaderStageFlags::FRAGMENT);
+
+  let bindings = [uniform_block_binding, sampler_binding];
+  let descriptor_set_layout_info
+          = vk::DescriptorSetLayoutCreateInfo::builder()
+                .bindings(&bindings);
+  let descriptor_set_layout = unsafe {
+    device.create_descriptor_set_layout(&descriptor_set_layout_info, None)
+  }?;
+
+  Ok(descriptor_set_layout)
+}
+
+
+
+//   To Vulkan, a "physical" device is the actual GPU, and a "logical"
+// device is per-process state that represents a connection to the GPU.
+// Before we can create a logical device, we must choose which physical
+// device to connect it to.
+#[allow(unsafe_code)]
+fn pick_vulkan_device(instance: &Instance, surface: &vk::SurfaceKHR)
+    -> Result<(vk::PhysicalDevice, QueueFamilyIndices, vk::SampleCountFlags)>
+{
+  let mut best_device = None;
+  let mut best_score = None;
+  let mut best_indices = None;
+  let mut best_sample_count = None;
+  let mut rejected = BTreeMap::new();
+
+  for device in unsafe { instance.enumerate_physical_devices() }? {
+    match score_vulkan_device(instance, surface, &device)? {
+      Acceptable::Accepted((new_score, new_indices, new_sample_count)) => {
+        if let Some(old_score) = best_score {
+          if new_score > old_score {
+            best_device = Some(device);
+            best_score = Some(new_score);
+            best_indices = Some(new_indices);
+            best_sample_count = Some(new_sample_count);
+          }
+        } else {
+          best_device = Some(device);
+          best_score = Some(new_score);
+          best_indices = Some(new_indices);
+          best_sample_count = Some(new_sample_count);
+        }
+      }
+      Acceptable::Rejected(reason) => {
+        let properties = unsafe {
+          instance.get_physical_device_properties(device)
+        };
+
+        let name = properties.device_name.to_string_lossy().into_owned();
+
+        rejected.insert(properties.device_id, (name, reason));
+      }
+    }
+  }
+
+  if let (Some(device), Some(indices), Some(sample_count))
+             = (best_device, best_indices, best_sample_count)
+  {
+    Ok((device, indices, sample_count))
+  } else if rejected.is_empty() {
+    Err(Error {
+      message: "The system has no GPUs of any kind.".to_string()
+    })
+  } else {
+    for (_, (name, reason)) in rejected {
+      eprintln!("Can't run on {} because: {}", name, reason);
+    }
+
+    Err(Error {
+      message: "The system has GPUs, but none are acceptable (see above)."
+               .to_string()
+    })
+  }
+}
+
+
+//   We're doing two tasks: Quantifying how strongly we prefer a device, and
+// deciding whether it's acceptable at all. If it's unacceptable, it's
+// possible there will be no acceptable devices, and in that case our caller
+// will want to print explanations, but otherwise it'll want to be quiet. So
+// the outer Result is whether we successfully evaluated the device, and the
+// inner Acceptable is whether we approve of it.
+//
+//   In the event that we find the device acceptable, we also return the
+// queue family indices we'd be using if we ultimately go with it. While
+// this is not strictly necessary, it's better to return them from here
+// than to recompute them later on the assumption it'll work out the same.
+#[allow(unsafe_code)]
+fn score_vulkan_device(instance: &Instance, surface: &vk::SurfaceKHR,
+                       physical_device: &vk::PhysicalDevice)
+    -> Result<Acceptable<(u64, QueueFamilyIndices, vk::SampleCountFlags)>>
+{
+  //   Not all devices support graphics, and not all devices support
+  // presenting to any given surface. We check whether this one is suitable
+  // by looking up the indices of the queue families we would use. If we
+  // ultimately use this device, we'll need these, so we make sure to return
+  // them.
+  let indices = match find_device_queue_family_indices(
+                          instance, surface, physical_device)?
+  {
+    Acceptable::Rejected(rationale) => {
+      return Ok(Acceptable::Rejected(rationale));
+    }
+    Acceptable::Accepted(indices) => indices
+  };
+
+  //   At this point we know the device meets our high-level requirements,
+  // so it's just a question of scoring.
+  let properties = unsafe {
+    instance.get_physical_device_properties(*physical_device)
+  };
+
+  let mut score = 0;
+  if properties.device_type == vk::PhysicalDeviceType::DISCRETE_GPU {
+    // If the user has a fancy GPU, they prefer it.
+    score += 128;
+  } else if properties.device_type
+                == vk::PhysicalDeviceType::INTEGRATED_GPU
+  {
+    // It's still hardware rendering.
+    score += 96;
+  } else if properties.device_type == vk::PhysicalDeviceType::VIRTUAL_GPU {
+    // Whatever it is, the user went to some trouble to set it up.
+    score += 64;
+  } else if properties.device_type == vk::PhysicalDeviceType::CPU {
+    // Software rendering is slow, but at least it's a known quantity.
+    score += 32;
+  }
+  // If it's none of those, we don't have enough information to know if
+  // that's good or bad, so we assume it's bad.
+
+  //   Some of our scoring will depend on what extensions the device
+  // supports, so we enumerate those.
+  let mut available_extensions = HashSet::new();
+  for extension in unsafe {
+    instance.enumerate_device_extension_properties(*physical_device, None)
+  }? {
+    available_extensions.insert(extension.extension_name);
+  }
+  let available_extensions = available_extensions;
+
+  if available_extensions.contains(&vk::KHR_SWAPCHAIN_EXTENSION.name) {
+    //   Double buffering is both quite a nice feature to have, and a good
+    // indicator that this is a "real" graphics card rather than some
+    // trivial weird thing.
+    //
+    //   With that said, however, it only counts if we're able to actually
+    // use it on the surface we have. Let's find out...
+    if let Acceptable::Accepted(_)
+           = PermanentGraphicsState::find_device_swapchain_features(
+                 instance, surface, physical_device)?
+    {
+      //   We don't count it for enough points to override a device type
+      // bracket, but it's good for a lot within the bracket.
+      score += 16;
+    }
+
+    //   This isn't disqualifying, so we don't worry about tracking the
+    // rationale. We'll deal with that later, if the device actually gets
+    // selected.
+  }
+
+  let features = unsafe {
+    instance.get_physical_device_features(*physical_device)
+  };
+  if features.sampler_anisotropy == vk::TRUE {
+    score += 1;
+  }
+
+  let sample_count = properties.limits.framebuffer_color_sample_counts
+                     & properties.limits.framebuffer_depth_sample_counts;
+  //   Happily, these bit flags are arranged in the obvious way, which lets us
+  // do some math on them. The max sample count is 64, so the max score bonus
+  // we give is 4.
+  let shift = sample_count.bits().ilog2() as u64;
+  score += shift;
+  let sample_count = vk::SampleCountFlags::from_bits(1 << shift).unwrap();
+
+  Ok(Acceptable::Accepted((score, indices, sample_count)))
+}
+
+
+#[allow(unsafe_code)]
+fn find_device_queue_family_indices(instance: &Instance,
+                                    surface: &vk::SurfaceKHR,
+                                    device: &vk::PhysicalDevice)
+    -> Result<Acceptable<QueueFamilyIndices>>
+{
+  //   We need a queue family that supports graphics drawing commands, and a
+  // queue family that supports presentation commands. These may or may not
+  // be the same family.
+  let mut graphics = None;
+  let mut presentation = None;
+
+  for (index, queue_family) in (unsafe {
+    instance.get_physical_device_queue_family_properties(*device)
+  }).into_iter().enumerate() {
+    if graphics.is_none()
+       && queue_family.queue_flags.contains(vk::QueueFlags::GRAPHICS)
+    {
+      graphics = Some(index as u32);
+    }
+
+    if presentation.is_none() && unsafe {
+      instance.get_physical_device_surface_support_khr(
+          *device, index as u32, *surface)
+    }? {
+      presentation = Some(index as u32);
+    }
+  }
+
+  if let Some(graphics) = graphics {
+    if let Some(presentation) = presentation {
+      Ok(Acceptable::Accepted(QueueFamilyIndices {
+        graphics, presentation
+      }))
+    } else {
+      Ok(Acceptable::Rejected(
+          "Doesn't support presenting to our window.".to_string()))
+    }
+  } else {
+    Ok(Acceptable::Rejected("Doesn't support graphics.".to_string()))
+  }
+}
+
+
+#[allow(unsafe_code)]
+extern "system" fn debug_messager_callback(
+    severity: vk::DebugUtilsMessageSeverityFlagsEXT,
+    flags: vk::DebugUtilsMessageTypeFlagsEXT,
+    data: *const vk::DebugUtilsMessengerCallbackDataEXT,
+    _context: *mut c_void) -> vk::Bool32
+{
+  //   Vulkan sends us everything, it's up to us to apply any filtering we
+  // want. The thing about this is that games need to be debuggable by end
+  // users, to diagnose compatibility issues and weird configurations, so we
+  // still want SOMETHING even when we're built in release mode.
+  //
+  //   For now, we'll see if we can get away without providing runtime config
+  // stuff for diagnostics. We set the threshold pretty high in release mode,
+  // on the theory that our own diagnostics should be sufficient.
+  //
+  //   Making this strategy work does rely on us actually checking error
+  // conditions and reporting them in useful ways, so that we only need
+  // Vulkan's messages for things we truly couldn't have anticipated. We do
+  // not take a more-is-better approach to diagnostics; the ideal would be to
+  // provide all the crucial information, and nothing else.
+  let threshold = if cfg!(feature = "vulkan-validation")
+                     || cfg!(debug_assertions)
+  {
+    vk::DebugUtilsMessageSeverityFlagsEXT::WARNING
+  } else {
+    vk::DebugUtilsMessageSeverityFlagsEXT::ERROR
+  };
+
+  if severity >= threshold {
+    let data = unsafe { *data };
+    let text = unsafe { CStr::from_ptr(data.message) }.to_string_lossy();
+
+    let label = if severity >= vk::DebugUtilsMessageSeverityFlagsEXT::ERROR {
+      "error"
+    } else if severity >= vk::DebugUtilsMessageSeverityFlagsEXT::WARNING {
+      "warning"
+    } else if severity >= vk::DebugUtilsMessageSeverityFlagsEXT::INFO {
+      "informational message"
+    } else {
+      "message of unknown, very minor significance"
+    };
+
+    eprintln!("Vulkan {}: {} (flags {:?})", label, text, flags);
+  }
+
+  //   A return value of true would tell the validation layer we're unhappy
+  // with it, for the sake of conformance testing. We're not a conformance
+  // test so anything it does is fine with us.
+  vk::FALSE
+}