[Vulkan] Vulkan Image View

// MIT License
//
// Copyright (c) 2024 Daemyung Jang
//
// 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.
 
#include <cassert>
#include <array>
#include <vector>
#include <iomanip>
 
#include "VkRenderer.h"
#include "VkUtil.h"
#include "AndroidOut.h"
 
using namespace std;
 
VkRenderer::VkRenderer(ANativeWindow *window) {
    // ================================================================================
    // 1. VkInstance 생성
    // ================================================================================
    // VkApplicationInfo 구조체 정의
    VkApplicationInfo applicationInfo{
        .sType = VK_STRUCTURE_TYPE_APPLICATION_INFO,
        .pApplicationName = "Practice Vulkan",
        .applicationVersion = VK_MAKE_API_VERSION(0, 0, 1, 0),
        .apiVersion = VK_MAKE_API_VERSION(0, 1, 3, 0)
    };
 
    // 사용할 수 있는 레이어를 얻어온다.
    uint32_t instanceLayerCount;
    VK_CHECK_ERROR(vkEnumerateInstanceLayerProperties(&instanceLayerCount, nullptr));
 
    vector<VkLayerProperties> instanceLayerProperties(instanceLayerCount);
    VK_CHECK_ERROR(vkEnumerateInstanceLayerProperties(&instanceLayerCount,
                                                      instanceLayerProperties.data()));
 
    // 활성화할 레이어의 이름을 배열로 만든다.
    vector<const char*> instanceLayerNames;
    for (const auto &layerProperty : instanceLayerProperties) {
        instanceLayerNames.push_back(layerProperty.layerName);
    }
 
    uint32_t instanceExtensionCount; // 사용 가능한 InstanceExtension 개수
    VK_CHECK_ERROR(vkEnumerateInstanceExtensionProperties(nullptr,
                                                          &instanceExtensionCount,
                                                          nullptr));
 
    vector<VkExtensionProperties> instanceExtensionProperties(instanceExtensionCount);
    VK_CHECK_ERROR(vkEnumerateInstanceExtensionProperties(nullptr,
                                                          &instanceExtensionCount,
                                                          instanceExtensionProperties.data()));
 
    vector<const char *> instanceExtensionNames; // instanceExtensionName을 담는 배열
    for (const auto &properties: instanceExtensionProperties) {
        if (properties.extensionName == string("VK_KHR_surface") ||
            properties.extensionName == string("VK_KHR_android_surface")) {
            instanceExtensionNames.push_back(properties.extensionName);
        }
    }
    assert(instanceExtensionNames.size() == 2); // 반드시 2개의 이름이 필요하기 때문에 확인
 
    // sType: 구조체의 타입, pApplicationInfo: 어플리케이션의 이름
    // enabledLayerCount, ppEnableLayerNames: 사용할 레이어의 정보를 정의
    VkInstanceCreateInfo instanceCreateInfo{
        .sType = VK_STRUCTURE_TYPE_INSTANCE_CREATE_INFO,
        .pApplicationInfo = &applicationInfo,
        .enabledLayerCount = static_cast<uint32_t>(instanceLayerNames.size()),
        .ppEnabledLayerNames = instanceLayerNames.data(),
        .enabledExtensionCount = static_cast<uint32_t>(instanceExtensionNames.size()),
        .ppEnabledExtensionNames = instanceExtensionNames.data()
    };
 
    // vkCreateInstance로 인스턴스 생성. 생성된 인스턴스가 mInstance에 쓰여진다.
    VK_CHECK_ERROR(vkCreateInstance(&instanceCreateInfo, nullptr, &mInstance));
 
 
    // ================================================================================
    // 2. VkPhysicalDevice 선택
    // ================================================================================
    uint32_t physicalDeviceCount;
    VK_CHECK_ERROR(vkEnumeratePhysicalDevices(mInstance, &physicalDeviceCount, nullptr));
 
    vector<VkPhysicalDevice> physicalDevices(physicalDeviceCount);
    VK_CHECK_ERROR(vkEnumeratePhysicalDevices(mInstance, &physicalDeviceCount, physicalDevices.data()));
 
    // 간단한 예제를 위해 첫 번째 VkPhysicalDevice를 사용
    mPhysicalDevice = physicalDevices[0];
 
    VkPhysicalDeviceProperties physicalDeviceProperties; // 이 구조체 안에 GPU에 필요한 모든 정보가 있다.
    vkGetPhysicalDeviceProperties(mPhysicalDevice, &physicalDeviceProperties);
 
    aout << "Selected Physical Device Information ↓" << endl;
    aout << setw(16) << left << " - Device Name: "
         << string_view(physicalDeviceProperties.deviceName) << endl;
    aout << setw(16) << left << " - Device Type: "
         << vkToString(physicalDeviceProperties.deviceType) << endl;
    aout << std::hex;
    aout << setw(16) << left << " - Device ID: " << physicalDeviceProperties.deviceID << endl;
    aout << setw(16) << left << " - Vendor ID: " << physicalDeviceProperties.vendorID << endl;
    aout << std::dec;
    aout << setw(16) << left << " - API Version: "
         << VK_API_VERSION_MAJOR(physicalDeviceProperties.apiVersion) << "."
         << VK_API_VERSION_MINOR(physicalDeviceProperties.apiVersion);
    aout << setw(16) << left << " - Driver Version: "
         << VK_API_VERSION_MAJOR(physicalDeviceProperties.driverVersion) << "."
         << VK_API_VERSION_MINOR(physicalDeviceProperties.driverVersion);
 
 
    // ================================================================================
    // 3. VkDevice 생성
    // ================================================================================
    uint32_t queueFamilyPropertiesCount;
 
    //---------------------------------------------------------------------------------
    //** queueFamily 속성을 조회
    // 사용 가능한 queueFamily의 수(=queueFamilyPropertiesCount)를 얻어온다.
    vkGetPhysicalDeviceQueueFamilyProperties(mPhysicalDevice, &queueFamilyPropertiesCount, nullptr);
 
    vector<VkQueueFamilyProperties> queueFamilyProperties(queueFamilyPropertiesCount);
    // 해당 queueFamily들의 속성을 배열에 얻어온다.
    vkGetPhysicalDeviceQueueFamilyProperties(mPhysicalDevice, &queueFamilyPropertiesCount, queueFamilyProperties.data());
    //---------------------------------------------------------------------------------
 
    // 특정 queueFamilyProperties가 VK_QUEUE_GRAPHICS_BIT를 지원하는지 확인.
    // 지원하는 queueFamilyProperties를 찾으면 break. queueFamily에 대한 정보는 mQueueFamilyIndex에 저장.
    for (mQueueFamilyIndex = 0;
         mQueueFamilyIndex != queueFamilyPropertiesCount; ++mQueueFamilyIndex) {
        if (queueFamilyProperties[mQueueFamilyIndex].queueFlags & VK_QUEUE_GRAPHICS_BIT) {
            break;
        }
    }
 
    // 생성할 큐를 정의
    const vector<float> queuePriorities{1.0};
    VkDeviceQueueCreateInfo deviceQueueCreateInfo{
            .sType = VK_STRUCTURE_TYPE_DEVICE_QUEUE_CREATE_INFO,
            .queueFamilyIndex = mQueueFamilyIndex,      // queueFamilyIndex
            .queueCount = 1,                            // 생성할 큐의 개수
            .pQueuePriorities = queuePriorities.data()  // 큐의 우선순위
    };
 
    uint32_t deviceExtensionCount; // 사용 가능한 deviceExtension 개수
    VK_CHECK_ERROR(vkEnumerateDeviceExtensionProperties(mPhysicalDevice,
                                                        nullptr,
                                                        &deviceExtensionCount,
                                                        nullptr));
 
    vector<VkExtensionProperties> deviceExtensionProperties(deviceExtensionCount);
    VK_CHECK_ERROR(vkEnumerateDeviceExtensionProperties(mPhysicalDevice,
                                                        nullptr,
                                                        &deviceExtensionCount,
                                                        deviceExtensionProperties.data()));
 
    vector<const char *> deviceExtensionNames;
    for (const auto &properties: deviceExtensionProperties) {
        if (properties.extensionName == string("VK_KHR_swapchain")) {
            deviceExtensionNames.push_back(properties.extensionName);
        }
    }
    assert(deviceExtensionNames.size() == 1); // VK_KHR_swapchain이 반드시 필요하기 때문에 확인
 
    // 생성할 Device 정의
    VkDeviceCreateInfo deviceCreateInfo{
            .sType = VK_STRUCTURE_TYPE_DEVICE_CREATE_INFO,
            .queueCreateInfoCount = 1,                   // 큐의 개수
            .pQueueCreateInfos = &deviceQueueCreateInfo, // 생성할 큐의 정보
            .enabledExtensionCount = static_cast<uint32_t>(deviceExtensionNames.size()),
            .ppEnabledExtensionNames = deviceExtensionNames.data() // 활성화하려는 deviceExtension들을 넘겨줌
    };
 
    // vkCreateDevice를 호출하여 Device 생성(= mDevice 생성)
    VK_CHECK_ERROR(vkCreateDevice(mPhysicalDevice, &deviceCreateInfo, nullptr, &mDevice));
    // 생성된 Device(= mDevice)로부터 큐를 vkGetDeviceQueue를 호출하여 얻어온다.
    vkGetDeviceQueue(mDevice, mQueueFamilyIndex, 0, &mQueue);
 
 
    // ================================================================================
    // 4. VkSurface 생성
    // ================================================================================
    VkAndroidSurfaceCreateInfoKHR surfaceCreateInfo{
            .sType = VK_STRUCTURE_TYPE_ANDROID_SURFACE_CREATE_INFO_KHR,
            .window = window
    };
 
    // surface 생성.
    VK_CHECK_ERROR(vkCreateAndroidSurfaceKHR(mInstance, &surfaceCreateInfo, nullptr, &mSurface));
 
    VkBool32 supported; // surface 지원 여부
    VK_CHECK_ERROR(vkGetPhysicalDeviceSurfaceSupportKHR(mPhysicalDevice,
                                                        mQueueFamilyIndex,
                                                        mSurface,
                                                        &supported)); // 지원 여부를 받아옴.
    assert(supported);
 
 
    // ================================================================================
    // 5. VkSwapchain 생성
    // ================================================================================
    VkSurfaceCapabilitiesKHR surfaceCapabilities;
    VK_CHECK_ERROR(vkGetPhysicalDeviceSurfaceCapabilitiesKHR(mPhysicalDevice,
                                                             mSurface,
                                                             &surfaceCapabilities));
 
    VkCompositeAlphaFlagBitsKHR compositeAlpha = VK_COMPOSITE_ALPHA_FLAG_BITS_MAX_ENUM_KHR;
    for (auto i = 0; i <= 4; ++i) {
        if (auto flag = 0x1u << i; surfaceCapabilities.supportedCompositeAlpha & flag) {
            compositeAlpha = static_cast<VkCompositeAlphaFlagBitsKHR>(flag);
            break;
        }
    }
    assert(compositeAlpha != VK_COMPOSITE_ALPHA_FLAG_BITS_MAX_ENUM_KHR);
 
    VkImageUsageFlags swapchainImageUsage = VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT | VK_IMAGE_USAGE_TRANSFER_DST_BIT;
    assert(surfaceCapabilities.supportedUsageFlags & VK_IMAGE_USAGE_COLOR_ATTACHMENT_BIT);
 
    uint32_t surfaceFormatCount = 0;
    VK_CHECK_ERROR(vkGetPhysicalDeviceSurfaceFormatsKHR(mPhysicalDevice,
                                                        mSurface,
                                                        &surfaceFormatCount,
                                                        nullptr));
 
    vector<VkSurfaceFormatKHR> surfaceFormats(surfaceFormatCount);
    VK_CHECK_ERROR(vkGetPhysicalDeviceSurfaceFormatsKHR(mPhysicalDevice,
                                                        mSurface,
                                                        &surfaceFormatCount,
                                                        surfaceFormats.data()));
 
    uint32_t surfaceFormatIndex = VK_FORMAT_MAX_ENUM;
    for (auto i = 0; i != surfaceFormatCount; ++i) {
        if (surfaceFormats[i].format == VK_FORMAT_R8G8B8A8_UNORM) {
            surfaceFormatIndex = i;
            break;
        }
    }
    assert(surfaceFormatIndex != VK_FORMAT_MAX_ENUM);
 
    uint32_t presentModeCount;
    VK_CHECK_ERROR(vkGetPhysicalDeviceSurfacePresentModesKHR(mPhysicalDevice,
                                                             mSurface,
                                                             &presentModeCount,
                                                             nullptr));
 
    vector<VkPresentModeKHR> presentModes(presentModeCount);
    VK_CHECK_ERROR(vkGetPhysicalDeviceSurfacePresentModesKHR(mPhysicalDevice,
                                                             mSurface,
                                                             &presentModeCount,
                                                             presentModes.data()));
 
    uint32_t presentModeIndex = VK_PRESENT_MODE_MAX_ENUM_KHR;
    for (auto i = 0; i != presentModeCount; ++i) {
        if (presentModes[i] == VK_PRESENT_MODE_FIFO_KHR) {
            presentModeIndex = i;
            break;
        }
    }
    assert(presentModeIndex != VK_PRESENT_MODE_MAX_ENUM_KHR);
 
    VkSwapchainCreateInfoKHR swapchainCreateInfo{
            .sType = VK_STRUCTURE_TYPE_SWAPCHAIN_CREATE_INFO_KHR,
            .surface = mSurface,
            .minImageCount = surfaceCapabilities.minImageCount,
            .imageFormat = surfaceFormats[surfaceFormatIndex].format,
            .imageColorSpace = surfaceFormats[surfaceFormatIndex].colorSpace,
            .imageExtent = surfaceCapabilities.currentExtent,
            .imageArrayLayers = 1,
            .imageUsage = swapchainImageUsage,
            .imageSharingMode = VK_SHARING_MODE_EXCLUSIVE,
            .preTransform = surfaceCapabilities.currentTransform,
            .compositeAlpha = compositeAlpha,
            .presentMode = presentModes[presentModeIndex]
    };
 
    VK_CHECK_ERROR(vkCreateSwapchainKHR(mDevice, &swapchainCreateInfo, nullptr, &mSwapchain));
 
    uint32_t swapchainImageCount;
    VK_CHECK_ERROR(vkGetSwapchainImagesKHR(mDevice, mSwapchain, &swapchainImageCount, nullptr));
 
    mSwapchainImages.resize(swapchainImageCount);
    VK_CHECK_ERROR(vkGetSwapchainImagesKHR(mDevice,
                                           mSwapchain,
                                           &swapchainImageCount,
                                           mSwapchainImages.data()));
 
 
    mSwapchainImageViews.resize(swapchainImageCount); // ImageView를 Swapchain의 개수만큼 생성
    for (auto i = 0; i != swapchainImageCount; ++i) {
        // ================================================================================
        // 6. VkImageView 생성
        // ================================================================================
        VkImageViewCreateInfo imageViewCreateInfo{ // 생성할 ImageView를 정의
                .sType = VK_STRUCTURE_TYPE_IMAGE_VIEW_CREATE_INFO,
                .image = mSwapchainImages[i],
                .viewType = VK_IMAGE_VIEW_TYPE_2D,
                .format = surfaceFormats[surfaceFormatIndex].format, // Swapchain 이미지 포맷과 동일한 포맷으로 설정
                .components = {
                        .r = VK_COMPONENT_SWIZZLE_R,
                        .g = VK_COMPONENT_SWIZZLE_G,
                        .b = VK_COMPONENT_SWIZZLE_B,
                        .a = VK_COMPONENT_SWIZZLE_A,
                },
                .subresourceRange = { // 모든 이미지에 대해서 이 이미지 뷰가 접근할 수 있도록 설정
                        .aspectMask = VK_IMAGE_ASPECT_COLOR_BIT,
                        .baseMipLevel = 0,
                        .levelCount = 1,
                        .baseArrayLayer = 0,
                        .layerCount = 1
                }
        };
 
        VK_CHECK_ERROR(vkCreateImageView(mDevice,
                                         &imageViewCreateInfo,
                                         nullptr,
                                         &mSwapchainImageViews[i])); // mSwapchainImageViews[i] 생성
    }
 
    // ================================================================================
    // 7. VkCommandPool 생성
    // ================================================================================
    VkCommandPoolCreateInfo commandPoolCreateInfo{
            .sType = VK_STRUCTURE_TYPE_COMMAND_POOL_CREATE_INFO,
            .flags = VK_COMMAND_POOL_CREATE_TRANSIENT_BIT |           // command buffer가 자주 변경될 것임을 알려줌
                     VK_COMMAND_POOL_CREATE_RESET_COMMAND_BUFFER_BIT, // command buffer를 개별적으로 초기화 가능하게 설정
            .queueFamilyIndex = mQueueFamilyIndex
    };
 
    VK_CHECK_ERROR(vkCreateCommandPool(mDevice, &commandPoolCreateInfo, nullptr, &mCommandPool)); // mCommandPool 생성
 
    // ================================================================================
    // 8. VkCommandBuffer 할당
    // ================================================================================
    VkCommandBufferAllocateInfo commandBufferAllocateInfo{ // 할당하려는 command buffer 정의
            .sType = VK_STRUCTURE_TYPE_COMMAND_BUFFER_ALLOCATE_INFO,
            .commandPool = mCommandPool,
            .level = VK_COMMAND_BUFFER_LEVEL_PRIMARY,
            .commandBufferCount = 1
    };
 
    VK_CHECK_ERROR(vkAllocateCommandBuffers(mDevice, &commandBufferAllocateInfo, &mCommandBuffer));
 
    // ================================================================================
    // 9. VkCommandBuffer 기록 시작
    // ================================================================================
    VkCommandBufferBeginInfo commandBufferBeginInfo{
            .sType = VK_STRUCTURE_TYPE_COMMAND_BUFFER_BEGIN_INFO,
            .flags = VK_COMMAND_BUFFER_USAGE_ONE_TIME_SUBMIT_BIT // 한 번만 기록되고 다시 리셋 될 것이라는 의미
    };
 
    // mCommandBuffer를 기록중인 상태로 변경.
    VK_CHECK_ERROR(vkBeginCommandBuffer(mCommandBuffer, &commandBufferBeginInfo));
 
    for (auto swapchainImage : mSwapchainImages) { // 스왑체인 이미지만큼 for문을 돈다.
        // ================================================================================
        // 10. VkImageLayout 변환
        // ================================================================================
        VkImageMemoryBarrier imageMemoryBarrierForPresentSwapchainImage{
                .sType = VK_STRUCTURE_TYPE_IMAGE_MEMORY_BARRIER,
                .srcAccessMask = 0,
                .dstAccessMask = 0,
                .oldLayout = VK_IMAGE_LAYOUT_UNDEFINED,
                .newLayout = VK_IMAGE_LAYOUT_PRESENT_SRC_KHR,
                .srcQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED,
                .dstQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED,
                .image = swapchainImage,
                .subresourceRange = {
                        .aspectMask = VK_IMAGE_ASPECT_COLOR_BIT,
                        .baseMipLevel = 0,
                        .levelCount = 1,
                        .baseArrayLayer = 0,
                        .layerCount = 1
                }
        };
 
        vkCmdPipelineBarrier(mCommandBuffer,
                             VK_PIPELINE_STAGE_TOP_OF_PIPE_BIT,
                             VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT,
                             0,
                             0,
                             nullptr,
                             0,
                             nullptr,
                             1,
                             &imageMemoryBarrierForPresentSwapchainImage);
    }
 
    // ================================================================================
    // 11. VkCommandBuffer 기록 종료
    // ================================================================================
    VK_CHECK_ERROR(vkEndCommandBuffer(mCommandBuffer)); // mCommandBuffer는 Executable 상태가 된다.
 
    // ================================================================================
    // 12. VkCommandBuffer 제출
    // ================================================================================
    VkSubmitInfo submitInfo{
            .sType = VK_STRUCTURE_TYPE_SUBMIT_INFO,
            .commandBufferCount = 1,
            .pCommandBuffers = &mCommandBuffer
    };
 
    // submitInfo 구조체를 넘김으로써 commandBuffer 정보를 queue에 제출
    VK_CHECK_ERROR(vkQueueSubmit(mQueue, 1, &submitInfo, VK_NULL_HANDLE));
    // commandBuffer를 vkQueueSubmit에 제출했지만 해당 Command buffer가 실행이 됐을지 안 됐을지 알 수 없다. CPU와 GPU는 따로따로 돌기 때문에 항상 실행이 됐다는 보장을 할 수 없다. 그래서 이를 보장하기 위해 vkQueueWaitIdle를 호출하여 이 queue에 제출한 Command buffer가 모두 다 실행되는 것을 보장한다.
    VK_CHECK_ERROR(vkQueueWaitIdle(mQueue));
 
 
    // ================================================================================
    // 13. VkFence 생성
    // ================================================================================
    VkFenceCreateInfo fenceCreateInfo{
        .sType = VK_STRUCTURE_TYPE_FENCE_CREATE_INFO
    }; // 생성할 Fence의 정보를 해당 구조체에서 정의
 
    VK_CHECK_ERROR(vkCreateFence(mDevice, &fenceCreateInfo, nullptr, &mFence)); // mFence 생성. flag에 아무것도 넣어주지 않았기 때문에 생성된 Fence의 초기 상태는 Unsignal 상태다.
 
 
    // ================================================================================
    // 14. VkSemaphore 생성
    // ================================================================================
    VkSemaphoreCreateInfo semaphoreCreateInfo{
            .sType = VK_STRUCTURE_TYPE_SEMAPHORE_CREATE_INFO,
    };
 
    VK_CHECK_ERROR(vkCreateSemaphore(mDevice, &semaphoreCreateInfo, nullptr, &mSemaphore));
}
 
VkRenderer::~VkRenderer() {
    for (auto imageView : mSwapchainImageViews) {
        vkDestroyImageView(mDevice, imageView, nullptr);
    }
    mSwapchainImageViews.clear();
    vkDestroySemaphore(mDevice, mSemaphore, nullptr);
    vkDestroyFence(mDevice, mFence, nullptr);
    vkFreeCommandBuffers(mDevice, mCommandPool, 1, &mCommandBuffer);
    vkDestroyCommandPool(mDevice, mCommandPool, nullptr);
    vkDestroySwapchainKHR(mDevice, mSwapchain, nullptr);
    vkDestroySurfaceKHR(mInstance, mSurface, nullptr);
    vkDestroyDevice(mDevice, nullptr); // Device 파괴. queue의 경우 Device를 생성하면서 생겼기 때문에 따로 파괴하는 API가 존재하지 않는다.
    vkDestroyInstance(mInstance, nullptr);
}
 
void VkRenderer::render() {
    // ================================================================================
    // 1. 화면에 출력할 수 있는 VkImage 얻기
    // ================================================================================
    uint32_t swapchainImageIndex;
    VK_CHECK_ERROR(vkAcquireNextImageKHR(mDevice,
                                         mSwapchain,
                                         UINT64_MAX,
                                         VK_NULL_HANDLE,
                                         mFence,                 // Fence 설정
                                         &swapchainImageIndex)); // 사용 가능한 이미지 변수에 담기
    auto swapchainImage = mSwapchainImages[swapchainImageIndex];
 
    // ================================================================================
    // 2. VkFence 기다린 후 초기화
    // ================================================================================
    // mFence가 Signal 될 때까지 기다린다.
    VK_CHECK_ERROR(vkWaitForFences(mDevice, 1, &mFence, VK_TRUE, UINT64_MAX));
    // mFence가 Siganl이 되면 vkResetFences를 호출해서 Fence의 상태를 다시 초기화한다.
    // 초기화하는 이유: vkAcquireNextImageKHR을 호출할 때 이 Fence의 상태는 항상 Unsignal 상태여야 하기 때문이다.
    VK_CHECK_ERROR(vkResetFences(mDevice, 1, &mFence));
 
    // ================================================================================
    // 3. VkCommandBuffer 초기화
    // ================================================================================
    vkResetCommandBuffer(mCommandBuffer, 0);
 
    // ================================================================================
    // 4. VkCommandBuffer 기록 시작
    // ================================================================================
    VkCommandBufferBeginInfo commandBufferBeginInfo{
            .sType = VK_STRUCTURE_TYPE_COMMAND_BUFFER_BEGIN_INFO,
            .flags = VK_COMMAND_BUFFER_USAGE_ONE_TIME_SUBMIT_BIT // 한 번만 기록되고 다시 리셋 될 것이라는 의미
    };
 
    // mCommandBuffer를 기록중인 상태로 변경.
    VK_CHECK_ERROR(vkBeginCommandBuffer(mCommandBuffer, &commandBufferBeginInfo));
 
    // ================================================================================
    // 5. VkImageLayout 변환
    // ================================================================================
    VkImageMemoryBarrier imageMemoryBarrierForClearColorImage{
            .sType = VK_STRUCTURE_TYPE_IMAGE_MEMORY_BARRIER,
            .srcAccessMask = VK_ACCESS_NONE,
            .dstAccessMask = VK_ACCESS_TRANSFER_WRITE_BIT,
            .oldLayout = VK_IMAGE_LAYOUT_PRESENT_SRC_KHR,
            .newLayout = VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL,
            .srcQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED,
            .dstQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED,
            .image = swapchainImage,
            .subresourceRange = {
                    .aspectMask = VK_IMAGE_ASPECT_COLOR_BIT,
                    .baseMipLevel = 0,
                    .levelCount = 1,
                    .baseArrayLayer = 0,
                    .layerCount = 1
            }
    };
 
    vkCmdPipelineBarrier(mCommandBuffer,
                         VK_PIPELINE_STAGE_TOP_OF_PIPE_BIT,
                         VK_PIPELINE_STAGE_TRANSFER_BIT,
                         0,
                         0,
                         nullptr,
                         0,
                         nullptr,
                         1,
                         &imageMemoryBarrierForClearColorImage);
 
    // ================================================================================
    // 6. Clear 색상 갱신
    // ================================================================================
    for (auto i = 0; i != 4; ++i) {
        mClearColorValue.float32[i] = fmodf(mClearColorValue.float32[i] + 0.01, 1.0);
    }
 
    // ================================================================================
    // 7. VkImage 색상 초기화
    // ================================================================================
    VkImageSubresourceRange imageSubresourceRange{
            .aspectMask = VK_IMAGE_ASPECT_COLOR_BIT,
            .baseMipLevel = 0,
            .levelCount = 1,
            .baseArrayLayer = 0,
            .layerCount = 1
    };
 
    vkCmdClearColorImage(mCommandBuffer,
                         swapchainImage,
                         VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL,
                         &mClearColorValue,
                         1,
                         &imageSubresourceRange);
 
    // ================================================================================
    // 8. VkImageLayout 변환
    // ================================================================================
    VkImageMemoryBarrier imageMemoryBarrierForPresentSwapchainImage{
            .sType = VK_STRUCTURE_TYPE_IMAGE_MEMORY_BARRIER,
            .srcAccessMask = VK_ACCESS_TRANSFER_WRITE_BIT,
            .dstAccessMask = 0,
            .oldLayout = VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL,
            .newLayout = VK_IMAGE_LAYOUT_PRESENT_SRC_KHR,
            .srcQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED,
            .dstQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED,
            .image = swapchainImage,
            .subresourceRange = {
                    .aspectMask = VK_IMAGE_ASPECT_COLOR_BIT,
                    .baseMipLevel = 0,
                    .levelCount = 1,
                    .baseArrayLayer = 0,
                    .layerCount = 1
            }
    };
 
    vkCmdPipelineBarrier(mCommandBuffer,
                         VK_PIPELINE_STAGE_TRANSFER_BIT,
                         VK_PIPELINE_STAGE_BOTTOM_OF_PIPE_BIT,
                         0,
                         0,
                         nullptr,
                         0,
                         nullptr,
                         1,
                         &imageMemoryBarrierForPresentSwapchainImage);
 
 
    // ================================================================================
    // 9. VkCommandBuffer 기록 종료
    // ================================================================================
    VK_CHECK_ERROR(vkEndCommandBuffer(mCommandBuffer)); // mCommandBuffer는 Executable 상태가 된다.
 
 
    // ================================================================================
    // 10. VkCommandBuffer 제출
    // ================================================================================
    VkSubmitInfo submitInfo{
            .sType = VK_STRUCTURE_TYPE_SUBMIT_INFO,
            .commandBufferCount = 1,
            .pCommandBuffers = &mCommandBuffer,
            .signalSemaphoreCount = 1,
            .pSignalSemaphores = &mSemaphore
    };
 
    // submitInfo 구조체를 넘김으로써 commandBuffer 정보를 queue에 제출
    VK_CHECK_ERROR(vkQueueSubmit(mQueue, 1, &submitInfo, VK_NULL_HANDLE));
    // commandBuffer를 vkQueueSubmit에 제출했지만 해당 Command buffer가 실행이 됐을지 안 됐을지 알 수 없다. CPU와 GPU는 따로따로 돌기 때문에 항상 실행이 됐다는 보장을 할 수 없다. 그래서 이를 보장하기 위해 vkQueueWaitIdle를 호출하여 이 queue에 제출한 Command buffer가 모두 다 실행되는 것을 보장한다.
    VK_CHECK_ERROR(vkQueueWaitIdle(mQueue));
 
 
    // ================================================================================
    // 11. VkImage 화면에 출력
    // ================================================================================
    VkPresentInfoKHR presentInfo{
            .sType = VK_STRUCTURE_TYPE_PRESENT_INFO_KHR,
            .swapchainCount = 1,
            .pWaitSemaphores = &mSemaphore,
            .swapchainCount = 1,
            .pSwapchains = &mSwapchain,
            .pImageIndices = &swapchainImageIndex
    };
 
    VK_CHECK_ERROR(vkQueuePresentKHR(mQueue, &presentInfo)); // 화면에 출력.
}