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‎guide/src/SUMMARY.md

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- [GLFW Window](initialization/glfw_window.md)
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- [Vulkan Instance](initialization/instance.md)
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- [Vulkan Surface](initialization/surface.md)
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- [Vulkan Physical Device](initialization/gpu.md)

‎guide/src/initialization/gpu.md

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# Vulkan Physical Device
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A [Physical Device](https://registry.khronos.org/vulkan/specs/latest/man/html/VkPhysicalDevice.html) represents a single complete implementation of Vulkan, for out intents and purposes a single GPU. (It could also be eg a software renderer like Mesa/lavapipe.) Some machines may have multiple Physical Devices available, like laptops with dual-GPUs. We need to select the one we want to use, given our constraints:
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1. Vulkan 1.3 must be supported
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1. Vulkan Swapchains must be supported
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1. A Vulkan Queue that supports Graphics and Transfer operations must be available
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1. It must be able to present to the previously created Vulkan Surface
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1. (Optional) Prefer discrete GPUs
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We wrap the actual Physical Device and a few other useful objects into `struct Gpu`. Since it will be accompanied by a hefty utility function, we put it in its own hpp/cpp files, and move the `vk_version_v` constant to this new header:
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```cpp
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constexpr auto vk_version_v = VK_MAKE_VERSION(1, 3, 0);
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struct Gpu {
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vk::PhysicalDevice device{};
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vk::PhysicalDeviceProperties properties{};
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vk::PhysicalDeviceFeatures features{};
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std::uint32_t queue_family{};
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};
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[[nodiscard]] auto get_suitable_gpu(vk::Instance instance,
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vk::SurfaceKHR surface) -> Gpu;
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```
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The implementation:
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```cpp
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auto lvk::get_suitable_gpu(vk::Instance const instance,
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vk::SurfaceKHR const surface) -> Gpu {
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auto const supports_swapchain = [](Gpu const& gpu) {
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static constexpr std::string_view name_v =
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VK_KHR_SWAPCHAIN_EXTENSION_NAME;
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static constexpr auto is_swapchain =
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[](vk::ExtensionProperties const& properties) {
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return properties.extensionName.data() == name_v;
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};
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auto const properties = gpu.device.enumerateDeviceExtensionProperties();
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auto const it = std::ranges::find_if(properties, is_swapchain);
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return it != properties.end();
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};
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auto const set_queue_family = [](Gpu& out_gpu) {
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static constexpr auto queue_flags_v =
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vk::QueueFlagBits::eGraphics | vk::QueueFlagBits::eTransfer;
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for (auto const [index, family] :
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std::views::enumerate(out_gpu.device.getQueueFamilyProperties())) {
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if ((family.queueFlags & queue_flags_v) == queue_flags_v) {
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out_gpu.queue_family = static_cast<std::uint32_t>(index);
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return true;
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}
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}
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return false;
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};
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auto const can_present = [surface](Gpu const& gpu) {
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return gpu.device.getSurfaceSupportKHR(gpu.queue_family, surface) ==
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vk::True;
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};
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auto fallback = Gpu{};
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for (auto const& device : instance.enumeratePhysicalDevices()) {
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auto gpu = Gpu{.device = device, .properties = device.getProperties()};
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if (gpu.properties.apiVersion < vk_version_v) { continue; }
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if (!supports_swapchain(gpu)) { continue; }
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if (!set_queue_family(gpu)) { continue; }
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if (!can_present(gpu)) { continue; }
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gpu.features = gpu.device.getFeatures();
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if (gpu.properties.deviceType == vk::PhysicalDeviceType::eDiscreteGpu) {
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return gpu;
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}
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// keep iterating in case we find a Discrete Gpu later.
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fallback = gpu;
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}
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if (fallback.device) { return fallback; }
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throw std::runtime_error{"No suitable Vulkan Physical Devices"};
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}
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```
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Finally, add a `Gpu` member in `App` and initialize it after `create_surface()`:
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```cpp
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create_surface();
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select_gpu();
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// ...
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void App::select_gpu() {
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m_gpu = get_suitable_gpu(*m_instance, *m_surface);
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std::println("Using GPU: {}",
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std::string_view{m_gpu.properties.deviceName});
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}
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```

‎src/app.cpp

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VULKAN_HPP_DEFAULT_DISPATCH_LOADER_DYNAMIC_STORAGE
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namespace lvk {
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namespace {
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constexpr auto vk_version_v = VK_MAKE_VERSION(1, 3, 0);
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} // namespace
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void App::run() {
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create_window();
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create_instance();
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create_surface();
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select_gpu();
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main_loop();
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}
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m_surface = glfw::create_surface(m_window.get(), *m_instance);
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}
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void App::select_gpu() {
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m_gpu = get_suitable_gpu(*m_instance, *m_surface);
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std::println("[lvk] Using GPU: {}",
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std::string_view{m_gpu.properties.deviceName});
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}
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void App::main_loop() {
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while (glfwWindowShouldClose(m_window.get()) == GLFW_FALSE) {
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glfwPollEvents();

‎src/app.hpp

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#pragma once
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#include <gpu.hpp>
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#include <vulkan/vulkan.hpp>
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#include <window.hpp>
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void create_window();
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void create_instance();
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void create_surface();
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void select_gpu();
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void main_loop();
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glfw::Window m_window{};
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vk::UniqueInstance m_instance{};
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vk::UniqueSurfaceKHR m_surface{};
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Gpu m_gpu{};
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};
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} // namespace lvk

‎src/gpu.cpp

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#include <gpu.hpp>
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#include <algorithm>
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#include <ranges>
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#include <stdexcept>
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auto lvk::get_suitable_gpu(vk::Instance const instance,
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vk::SurfaceKHR const surface) -> Gpu {
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auto const supports_swapchain = [](Gpu const& gpu) {
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static constexpr std::string_view name_v =
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VK_KHR_SWAPCHAIN_EXTENSION_NAME;
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static constexpr auto is_swapchain =
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[](vk::ExtensionProperties const& properties) {
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return properties.extensionName.data() == name_v;
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};
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auto const properties = gpu.device.enumerateDeviceExtensionProperties();
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auto const it = std::ranges::find_if(properties, is_swapchain);
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return it != properties.end();
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};
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auto const set_queue_family = [](Gpu& out_gpu) {
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static constexpr auto queue_flags_v =
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vk::QueueFlagBits::eGraphics | vk::QueueFlagBits::eTransfer;
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for (auto const [index, family] :
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std::views::enumerate(out_gpu.device.getQueueFamilyProperties())) {
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if ((family.queueFlags & queue_flags_v) == queue_flags_v) {
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out_gpu.queue_family = static_cast<std::uint32_t>(index);
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return true;
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}
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}
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return false;
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};
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auto const can_present = [surface](Gpu const& gpu) {
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return gpu.device.getSurfaceSupportKHR(gpu.queue_family, surface) ==
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vk::True;
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};
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auto fallback = Gpu{};
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for (auto const& device : instance.enumeratePhysicalDevices()) {
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auto gpu = Gpu{.device = device, .properties = device.getProperties()};
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if (gpu.properties.apiVersion < vk_version_v) { continue; }
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if (!supports_swapchain(gpu)) { continue; }
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if (!set_queue_family(gpu)) { continue; }
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if (!can_present(gpu)) { continue; }
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gpu.features = gpu.device.getFeatures();
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if (gpu.properties.deviceType == vk::PhysicalDeviceType::eDiscreteGpu) {
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return gpu;
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}
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// keep iterating in case we find a Discrete Gpu later.
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fallback = gpu;
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}
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if (fallback.device) { return fallback; }
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throw std::runtime_error{"No suitable Vulkan Physical Devices"};
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}

‎src/gpu.hpp

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#pragma once
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#include <vulkan/vulkan.hpp>
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namespace lvk {
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constexpr auto vk_version_v = VK_MAKE_VERSION(1, 3, 0);
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struct Gpu {
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vk::PhysicalDevice device{};
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vk::PhysicalDeviceProperties properties{};
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vk::PhysicalDeviceFeatures features{};
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std::uint32_t queue_family{};
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};
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[[nodiscard]] auto get_suitable_gpu(vk::Instance instance,
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vk::SurfaceKHR surface) -> Gpu;
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} // namespace lvk

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