// Copyright (c) 2016-2018 Khronos Group. This work is licensed under a
// Creative Commons Attribution 4.0 International License; see
// http://creativecommons.org/licenses/by/4.0/

include::meta/VK_KHX_device_group_creation.txt[]

*Last Modified Date*::
    2016-10-19
*IP Status*::
    No known IP claims.
*Contributors*::
  - Jeff Bolz, NVIDIA

This extension provides instance-level commands to enumerate groups of
physical devices, and to create a logical device from a subset of one of
those groups.
Such a logical device can then be used with new features in the
`<<VK_KHX_device_group>>` extension.

=== New Object Types

None.

=== New Enum Constants

  * Extending elink:VkStructureType:
  ** ename:VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_GROUP_PROPERTIES_KHX
  * Extending elink:VkMemoryHeapFlagBits
  ** ename:VK_MEMORY_HEAP_MULTI_INSTANCE_BIT_KHX


=== New Enums

None.

=== New Structures

  * slink:VkPhysicalDeviceGroupPropertiesKHX
  * slink:VkDeviceGroupDeviceCreateInfoKHX

=== New Functions

  * flink:vkEnumeratePhysicalDeviceGroupsKHX

=== Issues

None.

=== Examples

[source,c++]
----------------------------------------

    VkDeviceCreateInfo devCreateInfo = { VK_STRUCTURE_TYPE_DEVICE_CREATE_INFO };
    // (not shown) fill out devCreateInfo as usual.
    uint32_t deviceGroupCount = 0;
    VkPhysicalDeviceGroupPropertiesKHX *props = NULL;

    // Query the number of device groups
    vkEnumeratePhysicalDeviceGroupsKHX(g_vkInstance, &deviceGroupCount, NULL);

    // Allocate and initialize structures to query the device groups
    props = (VkPhysicalDeviceGroupPropertiesKHX *)malloc(deviceGroupCount*sizeof(VkPhysicalDeviceGroupPropertiesKHX));
    for (i = 0; i < deviceGroupCount; ++i) {
        props[i].sType = VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_GROUP_PROPERTIES_KHX;
        props[i].pNext = NULL;
    }
    vkEnumeratePhysicalDeviceGroupsKHX(g_vkInstance, &deviceGroupCount, props);

    // If the first device group has more than one physical device. create
    // a logical device using all of the physical devices.
    VkDeviceGroupDeviceCreateInfoKHX deviceGroupInfo = { VK_STRUCTURE_TYPE_DEVICE_GROUP_DEVICE_CREATE_INFO_KHX };
    if (props[0].physicalDeviceCount > 1) {
        deviceGroupInfo.physicalDeviceCount = props[0].physicalDeviceCount;
        deviceGroupInfo.pPhysicalDevices = props[0].physicalDevices;
        devCreateInfo.pNext = &deviceGroupInfo;
    }

    vkCreateDevice(props[0].physicalDevices[0], &devCreateInfo, NULL, &g_vkDevice);
    free(props);

----------------------------------------

=== Version History

 * Revision 1, 2016-10-19 (Jeff Bolz)
   - Internal revisions