VK_EXT_vertex_attribute_divisor

Other Extension Metadata

Last Modified Date

2018-08-03

IP Status

No known IP claims.

Contributors

• Vikram Kushwaha, NVIDIA
• Faith Ekstrand, Intel

Description

This extension allows instance-rate vertex attributes to be repeated for certain number of instances instead of advancing for every instance when instanced rendering is enabled.

New Structures

• VkVertexInputBindingDivisorDescriptionEXT
• Extending VkPhysicalDeviceFeatures2, VkDeviceCreateInfo:
  • VkPhysicalDeviceVertexAttributeDivisorFeaturesEXT
• Extending VkPhysicalDeviceProperties2:
  • VkPhysicalDeviceVertexAttributeDivisorPropertiesEXT
• Extending VkPipelineVertexInputStateCreateInfo:
  • VkPipelineVertexInputDivisorStateCreateInfoEXT

New Enum Constants

• VK_EXT_VERTEX_ATTRIBUTE_DIVISOR_EXTENSION_NAME
• VK_EXT_VERTEX_ATTRIBUTE_DIVISOR_SPEC_VERSION
• Extending VkStructureType:
  • VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_VERTEX_ATTRIBUTE_DIVISOR_FEATURES_EXT
  • VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_VERTEX_ATTRIBUTE_DIVISOR_PROPERTIES_EXT
  • VK_STRUCTURE_TYPE_PIPELINE_VERTEX_INPUT_DIVISOR_STATE_CREATE_INFO_EXT

Issues

1) What is the effect of a non-zero value for firstInstance?

RESOLVED: The Vulkan API should follow the OpenGL convention and offset attribute fetching by firstInstance while computing vertex attribute offsets.

2) Should zero be an allowed divisor?

RESOLVED: Yes. A zero divisor means the vertex attribute is repeated for all instances.

Examples

To create a vertex binding such that the first binding uses instanced rendering and the same attribute is used for every 4 draw instances, an application could use the following set of structures:

    const VkVertexInputBindingDivisorDescriptionEXT divisorDesc =
    {
        .binding = 0,
        .divisor = 4
    };

    const VkPipelineVertexInputDivisorStateCreateInfoEXT divisorInfo =
    {
        .sType = VK_STRUCTURE_TYPE_PIPELINE_VERTEX_INPUT_DIVISOR_STATE_CREATE_INFO_EXT,
        .pNext = NULL,
        .vertexBindingDivisorCount = 1,
        .pVertexBindingDivisors = &divisorDesc
    }

    const VkVertexInputBindingDescription binding =
    {
        .binding = 0,
        .stride = sizeof(Vertex),
        .inputRate = VK_VERTEX_INPUT_RATE_INSTANCE
    };

    const VkPipelineVertexInputStateCreateInfo viInfo =
    {
        .sType = VK_STRUCTURE_TYPE_PIPELINE_VERTEX_INPUT_CREATE_INFO,
        .pNext = &divisorInfo,
        ...
    };
    //...

Version History

• Revision 1, 2017-12-04 (Vikram Kushwaha)
  • First Version
• Revision 2, 2018-07-16 (Faith Ekstrand)
  • Adjust the interaction between divisor and firstInstance to match the OpenGL convention.
  • Disallow divisors of zero.
• Revision 3, 2018-08-03 (Vikram Kushwaha)
  • Allow a zero divisor.
  • Add a physical device features structure to query/enable this feature.