Understanding Vulkan uniform layout's 'set' index

Question

I've been following along in the (very awesome) nvpro raytracing tutorial and have a question about the way the CameraProperties uniform buffer is bound using layout(binding = 0, set = 1) - I understand the binding = 0, but why set = 1?

The tutorial says "The set = 1 comes from the fact that it is the second descriptor set passed to pipelineLayoutCreateInfo.setPSetLayouts", but when I look at HelloVulkan::createGraphicsPipeline() I see the layout count is one, and this is where m_descSetLayout (what binds the camera uniform buffer) is used. What am I missing?

The related section of the tutorial is here.

Thanks!

Sascha Willems Sascha Willems · Accepted Answer · 2020-12-21T06:14:30

See chapter 7.1:

  std::vector<vk::DescriptorSetLayout> rtDescSetLayouts = {m_rtDescSetLayout, m_descSetLayout};
  pipelineLayoutCreateInfo.setSetLayoutCount(static_cast<uint32_t>(rtDescSetLayouts.size()));
  pipelineLayoutCreateInfo.setPSetLayouts(rtDescSetLayouts.data());

The pipeline layout contains two descriptor set layouts, m_rtDescSetLayout for the acceleration structures at index 0 (set 0) and m_descSetLayout for the screne descriptors in index 1 (set 1). In Vulkan the set is automatically derived from a descriptor set layout's index in the pipeline layouts create info.

Understanding Vulkan uniform layout's 'set' index

1 Answers