Vulkan UBO传递错误

Question

我想将包含两个4x4矩阵的统一缓冲区对象传递给顶点着色器。我在C中声明了结构，如下所示：

struct PerRenderUBO
{
    glm::mat4 viewProjection;
    glm::mat4 projection; //unused
};

在GLSL中：

layout(std140, set = 0, binding = 0) uniform UBO {
    mat4 viewProjection;
    mat4 projection; //unused
} perRenderUBO;

但是，一旦我在UBO结构中声明了多个成员，一些对象就会由于错误的viewProjection矩阵而绘制错误。如果我注释掉PerRenderUBO结构和GLSL声明中的“projection”数据成员，所有内容都会正确渲染（尽管我甚至没有在着色器中使用投影）

这让我相信数据对齐肯定有问题。我已经用std140注释声明了布局。sizeof（PerRenderUBO）返回128。我试图将“投影”声明为float，但问题仍然存在。

以下是描述符集创建的最重要部分：

/** Create Layout **/
vk::DescriptorSetLayoutBinding perRenderUBOBinding;
perRenderUBOBinding.binding = 0;
perRenderUBOBinding.descriptorCount = 1;
perRenderUBOBinding.descriptorType = vk::DescriptorType::eUniformBuffer;
perRenderUBOBinding.stageFlags = vk::ShaderStageFlagBits::eVertex;
perRenderUBOBinding.pImmutableSamplers = nullptr;

std::vector<vk::DescriptorSetLayoutBinding> bindings{perRenderUBOBinding};

vk::DescriptorSetLayoutCreateInfo createInfo;
createInfo.bindingCount = bindings.size();
createInfo.pBindings = bindings.data();
this->perRenderUBOLayout = vkDevice->createDescriptorSetLayout(createInfo);

/** Create host-visible and host-coherent buffer **/
vk::BufferCreateInfo bufferCreateInfo;
bufferCreateInfo.size = sizeof(PerRenderUBO);
bufferCreateInfo.usage = vk::BufferUsageFlagBits::eUniformBuffer;
bufferCreateInfo.sharingMode = vk::SharingMode::eExclusive;
bufferCreateInfo.queueFamilyIndexCount = queueFamilyIndices.size();
bufferCreateInfo.pQueueFamilyIndices = queueFamilyIndices.data();
this->buffer = vkDevice->createBuffer(bufferCreateInfo);

vk::MemoryRequirements memoryRequirements = vkDevice->getBufferMemoryRequirements(this->buffer);
//allocates device memory as proposed in the specification (10.2 Device Memory)
this->bufferDeviceMemory = allocate(memoryRequirements, vk::MemoryPropertyFlags{vk::MemoryPropertyFlagBits::eHostVisible} | vk::MemoryPropertyFlags{vk::MemoryPropertyFlagBits::eHostCoherent});
vkDevice->bindBufferMemory(this->buffer, this->bufferDeviceMemory, 0);


this->descriptorPool = ...//create a descriptor pool for 1 uniform buffer
this->descriptorSet = ...//allocate descriptor set for above layout

vk::DescriptorBufferInfo bufferInfo;
bufferInfo.buffer = this->buffer;
bufferInfo.offset = 0;
bufferInfo.range = sizeof(PerRenderUBO);

vk::WriteDescriptorSet writeDescriptorSet;
writeDescriptorSet.dstSet = *this->descriptorSet;
writeDescriptorSet.dstBinding = 0;
writeDescriptorSet.dstArrayElement = 0;
writeDescriptorSet.descriptorType = vk::DescriptorType::eUniformBuffer;
writeDescriptorSet.descriptorCount = 1;
writeDescriptorSet.pBufferInfo = &bufferInfo;
writeDescriptorSet.pImageInfo = nullptr;
writeDescriptorSet.pTexelBufferView = nullptr;

vkDevice->updateDescriptorSets({writeDescriptorSet}, {});

在执行主draw命令buffer之前，我更新了PerRenderUBO的缓冲区，如下所示：

std::vector<PerRenderUBO> data; //contains 1 instance of PerRenderUBO
vk::DeviceSize offset = 0;
vk::DeviceSize size = data.size() * sizeof(PerRenderUBO);

void* memory = vkDevice->mapMemory(this->bufferDeviceMemory, offset, size);
std::memcpy(memory, data.data(), size);
this->deviceMemory->unmap();

我已经检查了好几次缓冲区大小和偏移量，一切看起来都很好。此外，由于每个绘图命令都绑定了相同的描述符集，并且一些对象渲染正确，我认为缓冲区中的数据本身必须正确。我错过了什么？

Answer 1

一些对象绘制不正确，一些对象绘制正确，这可能表明同步或缓冲区未按时更新存在问题。

首先，您需要通知驱动程序主机更新了缓冲区的哪些部分。我没有看到这样的代码，你也没有提到任何相关内容。这是通过刷新内存来完成的——需要调用vkFlushMappedMemoryRanges（）函数。

您可能还需要设置一个屏障，告知驾驶员缓冲区已被主机访问。但据我记忆所及，这种障碍是在命令缓冲区提交时隐式设置的。