1  include::meta/VK_EXT_vertex_attribute_divisor.txt[]
  2  
  3  *Last Modified Date*::
  4      2018-08-03
  5  *IP Status*::
  6      No known IP claims.
  7  *Contributors*::
  8    - Vikram Kushwaha, NVIDIA
  9    - Jason Ekstrand, Intel
 10  
 11  This extension allows instance-rate vertex attributes to be repeated for
 12  certain number of instances instead of advancing for every instance when
 13  instanced rendering is enabled.
 14  
 15  === New Object Types
 16  
 17  None.
 18  
 19  === New Enum Constants
 20  
 21  Extending elink:VkStructureType:
 22  
 23    ** ename:VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_VERTEX_ATTRIBUTE_DIVISOR_PROPERTIES_EXT
 24    ** ename:VK_STRUCTURE_TYPE_PIPELINE_VERTEX_INPUT_DIVISOR_STATE_CREATE_INFO_EXT
 25    ** ename:VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_VERTEX_ATTRIBUTE_DIVISOR_FEATURES_EXT
 26  
 27  === New Enums
 28  
 29  None.
 30  
 31  === New Structures
 32  
 33    * Extending slink:VkPipelineVertexInputStateCreateInfo:
 34    ** slink:VkPipelineVertexInputDivisorStateCreateInfoEXT
 35    * slink:VkPhysicalDeviceVertexAttributeDivisorPropertiesEXT
 36    * slink:VkVertexInputBindingDivisorDescriptionEXT
 37    * Extending slink:VkPhysicalDeviceFeatures2:
 38    ** slink:VkPhysicalDeviceVertexAttributeDivisorFeaturesEXT
 39  
 40  === New Functions
 41  
 42  None.
 43  
 44  === Issues
 45  
 46  1) What is the effect of a non-zero value for pname:firstInstance?
 47  
 48  *RESOLVED*: The Vulkan API should follow the OpenGL convention and offset
 49  attribute fetching by pname:firstInstance while computing vertex attribute
 50  offsets.
 51  
 52  2) Should zero be an allowed divisor?
 53  
 54  *RESOLVED*: Yes.
 55  A zero divisor means the vertex attribute is repeated for all instances.
 56  
 57  
 58  === Examples
 59  
 60  To create a vertex binding such that the first binding uses instanced
 61  rendering and the same attribute is used for every 4 draw instances, an
 62  application could use the following set of structures:
 63  
 64  
 65  [source,c++]
 66  ----------------------------------------
 67  
 68      const VkVertexInputBindingDivisorDescriptionEXT divisorDesc =
 69      {
 70          0,
 71          4
 72      };
 73  
 74      const VkPipelineVertexInputDivisorStateCreateInfoEXT divisorInfo =
 75      {
 76          VK_STRUCTURE_TYPE_PIPELINE_VERTEX_INPUT_DIVISOR_STATE_CREATE_INFO_EXT, // sType
 77          NULL,                                                             // pNext
 78          1,                                                                // vertexBindingDivisorCount
 79          &divisorDesc                                                      // pVertexBindingDivisors
 80      }
 81  
 82      const VkVertexInputBindingDescription binding =
 83      {
 84          0,                                                                // binding
 85          sizeof(Vertex),                                                   // stride
 86          VK_VERTEX_INPUT_RATE_INSTANCE                                     // inputRate
 87      };
 88  
 89      const VkPipelineVertexInputStateCreateInfo viInfo =
 90      {
 91          VK_STRUCTURE_TYPE_PIPELINE_VERTEX_INPUT_CREATE_INFO,              // sType
 92          &divisorInfo,                                                     // pNext
 93          ...
 94      };
 95      //...
 96  ----------------------------------------
 97  
 98  === Version History
 99  
100    * Revision 1, 2017-12-04 (Vikram Kushwaha)
101      - First Version
102    * Revision 2, 2018-07-16 (Jason Ekstrand)
103      - Adjust the interaction between pname:divisor and pname:firstInstance
104        to match the OpenGL convention.
105      - Disallow divisors of zero.
106    * Revision 3, 2018-08-03 (Vikram Kushwaha)
107      - Allow a zero divisor.
108      - Add a physical device features structure to query/enable this feature.