Vulkan编程指南

更新描述符

在createDescriptorSetLayout函数中填写用于组合图像采样器描述符的VkDescriptorSetLayoutBinding结构体信息。将下面的代码放在uniform缓冲绑定之后：

VkDescriptorSetLayoutBinding samplerLayoutBinding = {};
samplerLayoutBinding.binding = 1;
samplerLayoutBinding.descriptorCount = 1;
samplerLayoutBinding.descriptorType = VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER;
samplerLayoutBinding.pImmutableSamplers = nullptr;
samplerLayoutBinding.stageFlags = VK_SHADER_STAGE_FRAGMENT_BIT;

std::array<VkDescriptorSetLayoutBinding, 2> bindings = {uboLayoutBinding, samplerLayoutBinding};
VkDescriptorSetLayoutCreateInfo layoutInfo = {};
layoutInfo.sType = VK_STRUCTURE_TYPE_DESCRIPTOR_SET_LAYOUT_CREATE_INFO;
layoutInfo.bindingCount = static_cast<uint32_t>(bindings.size());
layoutInfo.pBindings = bindings.data();

设置stageFlags成员变量指明在片段着色器中使用组合图像采样器描述符。在顶点着色器也可以进行纹理采样，一个常见的用途是在顶点着色器中使用高度图纹理来对顶点进行变形。

现在在开启校验层的情况下编译运行程序，我们会得到描述符池不能分配该类型的描述符集这一信息。这一因为我们原来创建的描述符池对象并没有包含组合图像采样器描述符，为了解决这一问题，我们修改createDescriptorPool函数，添加一个用于组合图像采样器描述符的VkDescriptorPoolSize结构体信息：

std::array<VkDescriptorPoolSize, 2> poolSizes = {};
poolSizes[0].type = VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER;
poolSizes[0].descriptorCount = static_cast<uint32_t>(swapChainImages.size());
poolSizes[1].type = VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER;
poolSizes[1].descriptorCount = static_cast<uint32_t>(swapChainImages.size());

VkDescriptorPoolCreateInfo poolInfo = {};
poolInfo.sType = VK_STRUCTURE_TYPE_DESCRIPTOR_POOL_CREATE_INFO;
poolInfo.poolSizeCount = static_cast<uint32_t>(poolSizes.size());
poolInfo.pPoolSizes = poolSizes.data();
poolInfo.maxSets = static_cast<uint32_t>(swapChainImages.size());

最后，我们在createDescriptorSets函数中绑定图像和采样器到描述符集中的描述符：

for (size_t i = 0; i < swapChainImages.size(); i++) {
    VkDescriptorBufferInfo bufferInfo = {};
    bufferInfo.buffer = uniformBuffers[i];
    bufferInfo.offset = 0;
    bufferInfo.range = sizeof(UniformBufferObject);

    VkDescriptorImageInfo imageInfo = {};
    imageInfo.imageLayout = VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL;
    imageInfo.imageView = textureImageView;
    imageInfo.sampler = textureSampler;

        ...
}

需要使用VkDescriptorImageInfo结构体为组合图像采样器指定图像资源。

std::array<VkWriteDescriptorSet, 2> descriptorWrites = {};

descriptorWrites[0].sType = VK_STRUCTURE_TYPE_WRITE_DESCRIPTOR_SET;
descriptorWrites[0].dstSet = descriptorSets[i];
descriptorWrites[0].dstBinding = 0;
descriptorWrites[0].dstArrayElement = 0;
descriptorWrites[0].descriptorType = VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER;
descriptorWrites[0].descriptorCount = 1;
descriptorWrites[0].pBufferInfo = &bufferInfo;

descriptorWrites[1].sType = VK_STRUCTURE_TYPE_WRITE_DESCRIPTOR_SET;
descriptorWrites[1].dstSet = descriptorSets[i];
descriptorWrites[1].dstBinding = 1;
descriptorWrites[1].dstArrayElement = 0;
descriptorWrites[1].descriptorType = VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER;
descriptorWrites[1].descriptorCount = 1;
descriptorWrites[1].pImageInfo = &imageInfo;

vkUpdateDescriptorSets(device, static_cast<uint32_t>(descriptorWrites.size()), descriptorWrites.data(), 0, nullptr);

更新描述符需要使用图像资源信息。至此，我们就可以在着色器中使用描述符了。