ToxiCore - 9 months ago 76
C++ Question

# How to use a DepthBuffer as InputAttachment in Vulkan?

I have some trouble implementing my DepthBuffer as InputAttachment of a secondary subpass. I want to use the depth information of my first subpass. How can I archieve this? It seems that my current code gives me just an empty buffer..

My depth buffer is setup as follows:

create_info.imageType       = VK_IMAGE_TYPE_2D;
create_info.format          = VK_FORMAT_D32_SFLOAT;
create_info.mipLevels       = 1;
create_info.arrayLayers     = 1;
create_info.samples         = VK_SAMPLE_COUNT_1_BIT;
create_info.tiling          = VK_IMAGE_TILING_OPTIMAL;
create_info.usage           = VK_IMAGE_USAGE_DEPTH_STENCIL_ATTACHMENT_BIT | VK_IMAGE_USAGE_INPUT_ATTACHMENT_BIT;


I then use the following layout transition:

VkImageMemoryBarrier layout_transition_barrier{};
{
barrier.sType                   = VK_STRUCTURE_TYPE_IMAGE_MEMORY_BARRIER;
| VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT;
barrier.oldLayout               = VK_IMAGE_LAYOUT_UNDEFINED;
barrier.newLayout               = VK_IMAGE_LAYOUT_DEPTH_STENCIL_ATTACHMENT_OPTIMAL;
barrier.srcQueueFamilyIndex     = VK_QUEUE_FAMILY_IGNORED;
barrier.dstQueueFamilyIndex     = VK_QUEUE_FAMILY_IGNORED;
barrier.image                   = image;
barrier.subresourceRange        = { VK_IMAGE_ASPECT_DEPTH_BIT, 0, 1, 0, 1 };
}


This works totally fine for rendering..
The VkAttachmentReference I use has the layout
VK_IMAGE_LAYOUT_DEPTH_STENCIL_READ_ONLY_OPTIMAL
and I use it as an
VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER
.

In my fragment shader I then use
layout (set = 0, binding = 1) uniform sampler2D inputDepth;
to access it, however without any success.. the information I get is only zeros for any color channel.

Further I use this dependency:

VkSubpassDependency dependency{};
{
| VK_ACCESS_DEPTH_STENCIL_ATTACHMENT_WRITE_BIT;
dependency.dependencyFlags  = VK_DEPENDENCY_BY_REGION_BIT;
}


and this descritpion

static VkAttachmentDescription depth_input_attachment{};
{
depth_input_attachment.format           = VK_FORMAT_D32_SFLOAT;
depth_input_attachment.samples          = VK_SAMPLE_COUNT_1_BIT;
depth_input_attachment.storeOp          = VK_ATTACHMENT_STORE_OP_DONT_CARE;
depth_input_attachment.stencilStoreOp   = VK_ATTACHMENT_STORE_OP_DONT_CARE;
depth_input_attachment.initialLayout    = VK_IMAGE_LAYOUT_DEPTH_STENCIL_ATTACHMENT_OPTIMAL;
depth_input_attachment.finalLayout      = VK_IMAGE_LAYOUT_DEPTH_STENCIL_ATTACHMENT_OPTIMAL;
}


If you're doing subpasses (and not multiple render passes) and want to use your depth buffer as an inputAttachment and want to use an attachment as an input for a second subpass,

layout (set = 0, binding = 1) uniform sampler2D inputDepth

is not the correct syntax to sample from that in your shader.

Sampling from an input attachment requires a special syntax:

layout (input_attachment_index = n, binding = m) uniform subpassInput inputDepth;

This also requires a descriptor of type VK_DESCRIPTOR_TYPE_INPUT_ATTACHMENT instead of VK_DESCRIPTOR_TYPE_COMBINED_IMAGE_SAMPLER. Note that the actual descriptor for input attachments does not require a sampler.

If you're instead trying to sample your depth attachment in a second render pass, make sure that the storeOp of the attachment description is set to store.