vulkan/descriptorSet

参考Shader

layout(binding = 0) uniform UniformBufferObject {
    mat4 model;
    mat4 view;
    mat4 proj;
} ubo;

layout(location = 0) in vec2 inPosition;
layout(location = 1) in vec3 inColor;
layout(location = 2) in vec2 inTexCoord;

layout(location = 0) out vec3 fragColor;
layout(location = 1) out vec2 fragTexCoord;

void main() {
    gl_Position = ubo.proj * ubo.view * ubo.model * vec4(inPosition, 0.0, 1.0);
    fragColor = inColor;
    fragTexCoord = inTexCoord;
}

layout(location = 0) in vec2 fragTexCoord;
layout(location = 0) out vec4 outColor;
layout(binding = 1) uniform sampler2D texSampler;

void main() {
    outColor = texture(texSampler, fragTexCoord);
}

1. 是vs的uniform UniformBufferObject；需要vulkan传入对应的uniform buffer数据，

2. 是ps的uniform sampler2D texSampler，需要vulkan传入Sampler需要sample哪个image，以及sample的采样模式信息。

那么 vulkan 中需要对 uniform 进行抽象封装：

VkDescriptorSetLayoutBinding ubo　　=　　{};
    ubo.binding         = 0;
    ubo.descriptorType  = VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER;
    ubo.descriptorCount = 1;

VkDescriptorSetLayoutBinding samplerLayoutBinding{};
    samplerLayoutBinding.binding            = 1;
    samplerLayoutBinding.descriptorCount    = 1;
    samplerLayoutBinding.descriptorType     = VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER;//point out this descript type is sampler
    samplerLayoutBinding.pImmutableSamplers = nullptr;
    samplerLayoutBinding.stageFlags         = VK_SHADER_STAGE_FRAGMENT_BIT;

其中重要的信息点： binding 对应 layout(binding =  ? )

1. binding = 0 的 VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER 对象，只作用于vertex shader
2. binding = 1 的 VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER对象，作用于fragment shader

将这两类descriptor type封装到各自的VkDescriptorSetLay

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

    if (vkCreateDescriptorSetLayout(vulkanDevice->device, &layoutInfo, nullptr, &descriptorSetLayout) != VK_SUCCESS) {
        throw std::runtime_error("failed to create descriptor set layout!");
    }

这里需要是创建layout ，但是并没有给定数据，具体给什么数据，则由于 VkDescriptorSet 指定

std::vector<VkDescriptorSetLayout> layouts(MAX_FRAMES_IN_FLIGHT, descriptorSetLayout);
    VkDescriptorSetAllocateInfo allocInfo{};

    allocInfo.sType = VK_STRUCTURE_TYPE_DESCRIPTOR_SET_ALLOCATE_INFO;
    allocInfo.descriptorPool = descriptorPool;
    allocInfo.descriptorSetCount = static_cast<uint32_t>(MAX_FRAMES_IN_FLIGHT);
    allocInfo.pSetLayouts = layouts.data(); //layout has uniform format  information(descriptorSetLayout)

    //create descrpitsets array
    descriptorSets.resize(MAX_FRAMES_IN_FLIGHT);

    if (vkAllocateDescriptorSets(vulkanDevice->device, &allocInfo, descriptorSets.data()) != VK_SUCCESS) {
        throw std::runtime_error("failed to allocate descriptor sets!");
    }

数据上传：

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

        /*binding sampler and vkImage here*/
        VkDescriptorImageInfo imageInfo{};
        imageInfo.imageLayout = VK_IMAGE_LAYOUT_SHADER_READ_ONLY_OPTIMAL;
        imageInfo.imageView = textureImageView;
        imageInfo.sampler = textureSampler;

        //this struct link descript set we created before in this function and uniform buffer created before 
        std::array<VkWriteDescriptorSet, 2> descriptorWrites{};

        descriptorWrites[0].sType = VK_STRUCTURE_TYPE_WRITE_DESCRIPTOR_SET;
        descriptorWrites[0].dstSet = descriptorSets[i]; //get descriptor set object
        descriptorWrites[0].dstBinding = 0;//uniform buffer , now it is set as 0 in shader
        descriptorWrites[0].dstArrayElement = 0;//descriptor can be array so we specify 0
        descriptorWrites[0].descriptorType = VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER;//descriptor type is uniform 
        descriptorWrites[0].descriptorCount = 1;//
        descriptorWrites[0].pBufferInfo = &bufferInfo;//link uniform buffer

        descriptorWrites[1].sType = VK_STRUCTURE_TYPE_WRITE_DESCRIPTOR_SET;
        descriptorWrites[1].dstSet = descriptorSets[i];
        descriptorWrites[1].dstBinding = 1; //binding code relate to shader code : layout(binding = 1) uniform sampler2D texSampler;
        descriptorWrites[1].dstArrayElement = 0;
        descriptorWrites[1].descriptorType = VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER;//descriptor type is sampler 
        descriptorWrites[1].descriptorCount = 1;
        descriptorWrites[1].pImageInfo = &imageInfo;//link image info with vkImage and sampler

        //link descript set(include descript layout (uniform data format)) and uniform buffer
        vkUpdateDescriptorSets(vulkanDevice->device, static_cast<uint32_t>(descriptorWrites.size()), descriptorWrites.data(), 0, nullptr);
    }