Hey guys,

I create one dynamic uniform VkBuffer to upload uniforms. The memory managed by the VkBuffer is internally split into 3 chunks, where 3 is the maximum number of buffered frames. At frame start, I switch to the next chunk to suballocate memory from it during the frame. Each chunk occupies 1024 bytes. The total size occupied by VkBuffer is 3072 bytes.

I create one VkDescriptorSet, which contains one buffer descriptor of type VK_DESCRIPTOR_TYPE_UNIFORM_BUFFER_DYNAMIC pointing the uniform buffer.

VkDescriptorBufferInfo descriptorInfo;
descriptorInfo.buffer = uniformBuffer;
descriptorInfo.offset = 0;
descriptorInfo.range = 3072; // The total size of memory occupied by VkBuffer

On frame start

RotateBuffer(uniformBuffer, frameIndex);
// internalOffsetInBytes = frameIndex * chunkSizeInBytes;

On render

uint32_t uniformDataOffsetInBytes = SuballocateFromBuffer(uniformBuffer, uniformDataSizeInBytes);
// Update uniform data at uniformDataOffsetInBytes

vkCmdBindDescriptorSets(commandBuffer, VK_PIPELINE_BIND_POINT_GRAPHICS,
	pipelineLayout, descriptorSetIndex, 1, &descriptorSet, 1, &uniformDataOffsetInBytes);

I am receiving the following validation error "Descriptor in binding #0 index 0 is uses buffer VkBuffer 0xfe25f60000000013[Sample::m_pUniformBuffer] with dynamic offset 1024 combined with offset 0 and range 3072 that oversteps the buffer size of 3072."

Apperently, the validator is using dynamic offset with the range specificied on the descriptorInfo.

1. Should I set descriptorInfo.range to the size of one chunk? In this case, offset 0 is not valid anymore. Do I need to create a descriptor for each chunk then to have proper offset as well?
2. If I do more suballocations from each chunk, do I need to create a dedicated descriptor for each suballocation?
3. Can I use just one descriptor per chunk and set dynamic offset? If the validator uses dynamic offset in the 3rd chunk + size of the chunk itself, it will certainly go beyond the buffer limit as well.

In essence, I would like to suballocate memory from VkBuffer to upload the data. Is there possibility to do this with dynamicOffsets without creating descriptor for each allocation?

Thanks

@mjp Excellent, it works! Thanks

To add more info, 1024 is the byte size of the memory chunk, from which I do suballocation.

If I suballocate 256 bytes, I cannot use dynamic offset with a descriptor covering the whole 1024 byte range. Suppose I suballocate 256 bytes (now range [0..256) is occupied) and then suballocate 256 bytes more (range [256, 512)). In the second case, the check against 1024 bytes range will not succeed.

The size covered by the descriptor should be equal to the size of the suballocation.