Non uniform texture access in vulkan glsl - c++

Question

I am trying to write a compute shader that raytraces an image, pixels on the right of the yz plane sample from image A, those on the left from image B.
I don't want to have to sample both images so I am trying to use non uniform access by doing:
texture(textures[nonuniformEXT(sampler_id)], vec2(0.5));
and enabling the relevant extension in the shader. This triggers the following validaiton layer error:
Message: Validation Error: [ VUID-VkShaderModuleCreateInfo-pCode-01091 ] Object 0: handle = 0x55a1c21315d0, name = Logical device: AMD RADV RAVEN2, type = VK_OBJECT_TYPE_DEVICE; | MessageID = 0xa7bb8db6 | vkCreateShaderModule(): The SPIR-V Capability (SampledImageArrayNonUniformIndexing) was declared, but none of the requirements were met to use it. The Vulkan spec states: If pCode declares any of the capabilities listed in the SPIR-V Environment appendix, one of the corresponding requirements must be satisfied (https://vulkan.lunarg.com/doc/view/1.2.182.0/linux/1.2-extensions/vkspec.html#VUID-VkShaderModuleCreateInfo-pCode-01091)
If I read the docs it would seem this is a hardware feature, but someone said I can still have non uniform access if create the correct extension object. But I am not entirely sure how to do that.

Answer 1

You have to enable the feature at device creation.
You can check for support of the feature by calling vkGetPhysicalDeviceFeatures2 and following the pNext chain through to a VkPhysicalDeviceVulkan12Features, and checking that shaderSampledImageArrayNonUniformIndexing member is to VK_TRUE.
After that when creating the device with vkCreateDevice, inside the pCreateInfo structure, in the pNext chain you have to have a VkPhysicalDeviceVulkan12Features with shaderSampledImageArrayNonUniformIndexing set to VK_TRUE.
bool checkForNonUniformIndexing(VkPhysicalDevice physicalDevice)
{
VkPhysicalDeviceFeatures2 features;
vkGetPhysicalDeviceFeatures2(physicalDevice, &features);
if(features.sType != VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_FEATURES_2)
{
return false;
}
const VkPhysicalDeviceFeatures2* next = &features;
do
{
// We know the type of the struct based on the `sType` member, but the first
// two fields are the same in all of these structs. There may be a more appropriate
// generic structure to use, but as long as we don't access any further members
// we should be mostly fine.
next = reinterpret_cast<const VkPhysicalDeviceFeatures*>(next->pNext);
if(next.sType == VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_VULKAN_1_2_FEATURES)
{
const VkPhysicalDeviceVulkan12Features* pVk12Features = reinterpret_cast<const VkPhysicalDeviceVulkan12Features*>(next);
return next.shaderSampledImageArrayNonUniformIndexing == VK_TRUE;
}
} while(next);
return false;
}
VkDevice* createDevice(VkPhysicalDevice physicalDevice, const VkAllocationCallbacks* pAllocator)
{
VkPhysicalDeviceVulkan12Features features;
features.sType = VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_VULKAN_1_2_FEATURES;
features.shaderSampledImageArrayNonUniformIndexing = VK_TRUE;
VkDeviceCreateInfo createInfo;
createInfo.sType = VK_STRUCTURE_TYPE_DEVICE_CREATE_INFO;
createInfo.pNext = &features;
// Setting other create data
VkDevice device;
vkCreateDevice(physicalDevice, &createInfo, pAllocator, &device);
// Error checking
return device;
}