Vulkan 实现绘制到纹理的操作，给出简单的demo

以下是一个简单的Vulkan实现绘制到纹理的demo:

// 初始化Vulkan设备和图像
// ...

// 创建纹理图像
VkImageCreateInfo imageCreateInfo = {};
imageCreateInfo.sType = VK_STRUCTURE_TYPE_IMAGE_CREATE_INFO;
imageCreateInfo.imageType = VK_IMAGE_TYPE_2D;
imageCreateInfo.format = VK_FORMAT_R8G8B8A8_UNORM;
imageCreateInfo.extent.width = 512;
imageCreateInfo.extent.height = 512;
imageCreateInfo.extent.depth = 1;
imageCreateInfo.mipLevels = 1;
imageCreateInfo.arrayLayers = 1;
imageCreateInfo.samples = VK_SAMPLE_COUNT_1_BIT;
imageCreateInfo.tiling = VK_IMAGE_TILING_OPTIMAL;
imageCreateInfo.usage = VK_IMAGE_USAGE_TRANSFER_DST_BIT | VK_IMAGE_USAGE_SAMPLED_BIT;
vkCreateImage(device, &imageCreateInfo, nullptr, &textureImage);

// 分配内存并绑定纹理图像
VkMemoryRequirements memRequirements;
vkGetImageMemoryRequirements(device, textureImage, &memRequirements);
VkMemoryAllocateInfo allocInfo = {};
allocInfo.sType = VK_STRUCTURE_TYPE_MEMORY_ALLOCATE_INFO;
allocInfo.allocationSize = memRequirements.size;
allocInfo.memoryTypeIndex = findMemoryType(physicalDevice, memRequirements.memoryTypeBits, VK_MEMORY_PROPERTY_DEVICE_LOCAL_BIT);
vkAllocateMemory(device, &allocInfo, nullptr, &textureImageMemory);
vkBindImageMemory(device, textureImage, textureImageMemory, 0);

// 创建图像视图
VkImageViewCreateInfo viewCreateInfo = {};
viewCreateInfo.sType = VK_STRUCTURE_TYPE_IMAGE_VIEW_CREATE_INFO;
viewCreateInfo.image = textureImage;
viewCreateInfo.viewType = VK_IMAGE_VIEW_TYPE_2D;
viewCreateInfo.format = VK_FORMAT_R8G8B8A8_UNORM;
viewCreateInfo.subresourceRange.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT;
viewCreateInfo.subresourceRange.baseMipLevel = 0;
viewCreateInfo.subresourceRange.levelCount = 1;
viewCreateInfo.subresourceRange.baseArrayLayer = 0;
viewCreateInfo.subresourceRange.layerCount = 1;
vkCreateImageView(device, &viewCreateInfo, nullptr, &textureImageView);

// 创建帧缓冲区
VkFramebufferCreateInfo framebufferCreateInfo = {};
framebufferCreateInfo.sType = VK_STRUCTURE_TYPE_FRAMEBUFFER_CREATE_INFO;
framebufferCreateInfo.renderPass = renderPass;
framebufferCreateInfo.attachmentCount = 1;
framebufferCreateInfo.pAttachments = &textureImageView;
framebufferCreateInfo.width = 512;
framebufferCreateInfo.height = 512;
framebufferCreateInfo.layers = 1;
vkCreateFramebuffer(device, &framebufferCreateInfo, nullptr, &framebuffer);

// 创建命令池和命令缓冲区
// ...

// 开始记录命令缓冲区
VkCommandBufferBeginInfo beginInfo = {};
beginInfo.sType = VK_STRUCTURE_TYPE_COMMAND_BUFFER_BEGIN_INFO;
vkBeginCommandBuffer(commandBuffer, &beginInfo);

// 转换图像布局
VkImageMemoryBarrier barrier = {};
barrier.sType = VK_STRUCTURE_TYPE_IMAGE_MEMORY_BARRIER;
barrier.oldLayout = VK_IMAGE_LAYOUT_UNDEFINED;
barrier.newLayout = VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL;
barrier.srcQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED;
barrier.dstQueueFamilyIndex = VK_QUEUE_FAMILY_IGNORED;
barrier.image = textureImage;
barrier.subresourceRange.aspectMask = VK_IMAGE_ASPECT_COLOR_BIT;
barrier.subresourceRange.baseMipLevel = 0;
barrier.subresourceRange.levelCount = 1;
barrier.subresourceRange.baseArrayLayer = 0;
barrier.subresourceRange.layerCount = 1;
barrier.srcAccessMask = 0;
barrier.dstAccessMask = VK_ACCESS_TRANSFER_WRITE_BIT;
vkCmdPipelineBarrier(commandBuffer, VK_PIPELINE_STAGE_TOP_OF_PIPE_BIT, VK_PIPELINE_STAGE_TRANSFER_BIT, 0, 0, nullptr, 0, nullptr, 1, &barrier);

// 绑定渲染目标为纹理图像
VkRenderPassBeginInfo renderPassBeginInfo = {};
renderPassBeginInfo.sType = VK_STRUCTURE_TYPE_RENDER_PASS_BEGIN_INFO;
renderPassBeginInfo.renderPass = renderPass;
renderPassBeginInfo.framebuffer = framebuffer;
renderPassBeginInfo.renderArea.offset.x = 0;
renderPassBeginInfo.renderArea.offset.y = 0;
renderPassBeginInfo.renderArea.extent.width = 512;
renderPassBeginInfo.renderArea.extent.height = 512;
VkClearValue clearValue = {0.0f, 0.0f, 0.0f, 1.0f};
renderPassBeginInfo.clearValueCount = 1;
renderPassBeginInfo.pClearValues = &clearValue;
vkCmdBeginRenderPass(commandBuffer, &renderPassBeginInfo, VK_SUBPASS_CONTENTS_INLINE);

// 绘制场景
// ...

// 结束渲染
vkCmdEndRenderPass(commandBuffer);

// 转换图像布局
barrier.oldLayout = VK_IMAGE_LAYOUT_TRANSFER_DST_OPTIMAL;
barrier.newLayout = VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL;
barrier.srcAccessMask = VK_ACCESS_TRANSFER_WRITE_BIT;
barrier.dstAccessMask = VK_ACCESS_SHADER_READ_BIT;
vkCmdPipelineBarrier(commandBuffer, VK_PIPELINE_STAGE_TRANSFER_BIT, VK_PIPELINE_STAGE_FRAGMENT_SHADER_BIT, 0, 0, nullptr, 0, nullptr, 1, &barrier);

// 完成命令缓冲区
vkEndCommandBuffer(commandBuffer);

// 提交命令
VkSubmitInfo submitInfo = {};
submitInfo.sType = VK_STRUCTURE_TYPE_SUBMIT_INFO;
submitInfo.commandBufferCount = 1;
submitInfo.pCommandBuffers = &commandBuffer;
vkQueueSubmit(queue, 1, &submitInfo, VK_NULL_HANDLE);
vkQueueWaitIdle(queue);

在这个demo中，我们创建了一个大小为512x512的纹理图像，并且将其绑定到帧缓冲区。然后我们使用命令缓冲区将场景渲染到帧缓冲区，最后将帧缓冲区中的图像拷贝到纹理图像中。注意，在拷贝之前，我们需要将纹理图像的布局从未定义的状态转换为可写入的状态，拷贝结束后，我们需要将纹理图像的布局从可写入的状态转换为只读状态。