Low maxVariableDescriptorCount being reported

[MennoVink]

I'm receiving a rather low variable descriptor count which i expected to be higher.

I'm on Intel Iris 6100 and these are my limits:

maxPerStageDescriptorSamplers	uint32_t	16
maxPerStageDescriptorUniformBuffers	uint32_t	31
maxPerStageDescriptorStorageBuffers	uint32_t	31
maxPerStageDescriptorSampledImages	uint32_t	128
maxPerStageDescriptorStorageImages	uint32_t	8
maxPerStageDescriptorInputAttachments	uint32_t	128
maxPerStageResources	uint32_t	159
maxDescriptorSetSamplers	uint32_t	80
maxDescriptorSetUniformBuffers	uint32_t	155
maxDescriptorSetUniformBuffersDynamic	uint32_t	155
maxDescriptorSetStorageBuffers	uint32_t	155
maxDescriptorSetStorageBuffersDynamic	uint32_t	155
maxDescriptorSetSampledImages	uint32_t	640
maxDescriptorSetStorageImages	uint32_t	40
maxDescriptorSetInputAttachments	uint32_t	640

The values important to me are 16 samplers and 128 sampled images (both per-stage).
This is the layout for my descriptor set (glsl):

struct Constants
{
	mat4 world;
	int albedoIndex;
};
layout( std430, set = 0, binding = 0 ) readonly buffer buf
{
	Constants constants[];
};
layout( set = 0, binding = 1) uniform sampler albedoSampler;
layout( set = 0, binding = 2 ) uniform texture2D albedoImages[];

My layout bindings match this and i have bindFlags of 0, 0, 8 (variable only for the albedoImages).

Now when i call getDescriptorSetLayoutSupport attaching a DescriptorSetVariableDescriptorCountLayoutSupportEXT, i get the maximum variable count being 15.

Where does this 15 come from? How come it doesn't tell me that i can use 128 sampled images?

*edit: To add insult to injury, if i ask whether or not a layout using those 15 descriptors is supported it still tells me no. 14 is the highest amount that's reported as being supported. This seems to me like the same off-by-one issue i reported here #1696.

[MennoVink]

I tried to get this to run in the cube example but it's configured to disallow debugging so not sure how to recreate it there.

Here's what i've got so far:

    	VkDescriptorSetLayoutBinding bindings[ 3 ] = {};
    	bindings[ 0 ].binding = 0;
    	bindings[ 0 ].descriptorType = VK_DESCRIPTOR_TYPE_STORAGE_BUFFER;
    	bindings[ 0 ].descriptorCount = 1;
    	bindings[ 0 ].stageFlags = VK_SHADER_STAGE_VERTEX_BIT | VK_SHADER_STAGE_FRAGMENT_BIT;

    	bindings[ 1 ].binding = 1;
    	bindings[ 1 ].descriptorType = VK_DESCRIPTOR_TYPE_SAMPLER;
    	bindings[ 1 ].descriptorCount = 1;
    	bindings[ 1 ].stageFlags = VK_SHADER_STAGE_VERTEX_BIT | VK_SHADER_STAGE_FRAGMENT_BIT;

    	bindings[ 2 ].binding = 2;
    	bindings[ 2 ].descriptorType = VK_DESCRIPTOR_TYPE_SAMPLED_IMAGE;
    	bindings[ 2 ].descriptorCount = 0;
    	bindings[ 2 ].stageFlags = VK_SHADER_STAGE_VERTEX_BIT | VK_SHADER_STAGE_FRAGMENT_BIT;

		VkDescriptorSetLayoutCreateInfo setLayoutCreateInfo = {};
		setLayoutCreateInfo.sType = VK_STRUCTURE_TYPE_DESCRIPTOR_SET_LAYOUT_CREATE_INFO;
		setLayoutCreateInfo.bindingCount = 3;
		setLayoutCreateInfo.pBindings = bindings;

		VkDescriptorBindingFlags bindingFlags[ 3 ] = {};
		bindingFlags[ 2 ] = VK_DESCRIPTOR_BINDING_VARIABLE_DESCRIPTOR_COUNT_BIT;

		VkDescriptorSetLayoutBindingFlagsCreateInfo bindingFlagsCreateInfo = {};
		bindingFlagsCreateInfo.sType = VK_STRUCTURE_TYPE_DESCRIPTOR_SET_LAYOUT_BINDING_FLAGS_CREATE_INFO;
		bindingFlagsCreateInfo.bindingCount = 3;
		bindingFlagsCreateInfo.pBindingFlags = bindingFlags;
		setLayoutCreateInfo.pNext = &bindingFlagsCreateInfo;

		VkDescriptorSetVariableDescriptorCountLayoutSupport variableCountSupport = {};
		variableCountSupport.sType = VK_STRUCTURE_TYPE_DESCRIPTOR_SET_VARIABLE_DESCRIPTOR_COUNT_LAYOUT_SUPPORT;
		VkDescriptorSetLayoutSupport descriptorSupport = {};
		descriptorSupport.sType = VK_STRUCTURE_TYPE_DESCRIPTOR_SET_LAYOUT_SUPPORT;
		descriptorSupport.pNext = &variableCountSupport;

		vkGetDescriptorSetLayoutSupport( demo->device, &setLayoutCreateInfo, &descriptorSupport );
		assert( variableCountSupport.maxVariableDescriptorCount == 128 );

Obviously it also needs the indexing features:

	VkPhysicalDeviceDescriptorIndexingFeatures indexingFeatures = {};
	indexingFeatures.sType = VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_DESCRIPTOR_INDEXING_FEATURES;
	indexingFeatures.runtimeDescriptorArray = true;
	indexingFeatures.descriptorBindingVariableDescriptorCount = true;
	VkPhysicalDeviceFeatures2 enabledFeatures2 = {};
	enabledFeatures2.sType = VK_STRUCTURE_TYPE_PHYSICAL_DEVICE_FEATURES_2;
	enabledFeatures2.pNext = &indexingFeatures;

And the extension:

		for (uint32_t i = 0; i < device_extension_count; i++) {
			if (!strcmp(VK_EXT_DESCRIPTOR_INDEXING_EXTENSION_NAME, device_extensions[i].extensionName)) {
				demo->extension_names[demo->enabled_extension_count++] = VK_EXT_DESCRIPTOR_INDEXING_EXTENSION_NAME;
			}
		}