AccelerationStructure is impossible to build due to a dependency cycle

[atynagano]

Template

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If you can provide more detailed information than the template allows for, please ignore the template and present all of your findings.

• Version of vulkano: a1dca42
• OS: TODO
• GPU (the selected PhysicalDevice): TODO
• GPU Driver: TODO
• Upload of a reasonably minimal complete main.rs file that demonstrates the issue: TODO

Issue

Is there any acceleration structure example? I cannot find the way to build AS.
To build AS, commonly vkGetAccelerationStructureBuildSizesKHR() is called first with VkAccelerationStructureBuildGeometryInfoKHR.dstAccelerationStructure=scratchData=empty to acquire the size requirements for AS.

	// Get the size requirements for buffers involved in the acceleration structure build process
	VkAccelerationStructureBuildGeometryInfoKHR acceleration_structure_build_geometry_info{};
	acceleration_structure_build_geometry_info.sType         = VK_STRUCTURE_TYPE_ACCELERATION_STRUCTURE_BUILD_GEOMETRY_INFO_KHR;
	acceleration_structure_build_geometry_info.type          = VK_ACCELERATION_STRUCTURE_TYPE_BOTTOM_LEVEL_KHR;
	acceleration_structure_build_geometry_info.flags         = VK_BUILD_ACCELERATION_STRUCTURE_PREFER_FAST_TRACE_BIT_KHR;
	acceleration_structure_build_geometry_info.geometryCount = 1;
	acceleration_structure_build_geometry_info.pGeometries   = &acceleration_structure_geometry;

	const uint32_t primitive_count = 1;

	VkAccelerationStructureBuildSizesInfoKHR acceleration_structure_build_sizes_info{};
	acceleration_structure_build_sizes_info.sType = VK_STRUCTURE_TYPE_ACCELERATION_STRUCTURE_BUILD_SIZES_INFO_KHR;
	vkGetAccelerationStructureBuildSizesKHR(
	    device->get_handle(),
	    VK_ACCELERATION_STRUCTURE_BUILD_TYPE_DEVICE_KHR,
	    &acceleration_structure_build_geometry_info,
	    &primitive_count,
	    &acceleration_structure_build_sizes_info);

But current vulkano implementation requires AccelerationStructureBuildGeometryInfo.dst_acceleration_structure and .scratch_data not to be empty. So I think it's almost impossible to create AS without creating AS.

    let build_info = AccelerationStructureBuildGeometryInfo {
        flags: BuildAccelerationStructureFlags::PREFER_FAST_TRACE,
        mode: BuildAccelerationStructureMode::Build,
        ..AccelerationStructureBuildGeometryInfo::new(
            dst_acceleration_structure,
            geometries,
            scratch_data,
        )
    };

    let size = device.acceleration_structure_build_sizes(
        AccelerationStructureBuildType::HostOrDevice,
        &build_info,
        &[1],
    ).unwrap();

#2213

[marc0246]

An example is indeed greatly needed.

[marc0246]

The tags I added are not related to the example though, rather what you're saying needs fixing.

[Rua]

I've made a PR to fix the issue, but I think it demonstrates that I really don't know much about how acceleration structures are used in practice. Would you be willing to write an example for Vulkano?

[marc0246]

I made an issue to track the state of the example separately: #2308.