vk_raytrace_displacement

This sample demonstrates the use of the heightmap_rtx library to raytrace dynamically displaced geometry. heightmap_rtx is a small Vulkan library to displace raytraced triangles with a heightmap. It uses NVIDIA Micro-Mesh (Toolkit) internally.

A notable feature of this sample is animation. A single and static VkCommandBuffer that heightmap_rtx populates is resubmitted each frame before building the acceleration structure. This allows convenient animation without any mid-frame resource allocation for building the Micro-Map.

Requirements

heightmap_rtx is a submodule. Run git submodule update --init --recursive.

Along with other nvpro samples, nvpro_core and the VulkanSDK are required to build this project. Cmake will look in the parent directory for nvpro_core and the VulkanSDK is typically found via environment variables.

VK_NV_displacement_micromap is required. See device support.

Important

VK_NV_displacement_micromap likely requires recent NVIDIA vulkan beta drivers (>= 537.96) and VulkanSDK (>= 1.3.268.0), particularly for GLSL NV_displacement_micromap support.

Motivation

To render displacement with rasterization, one might use a tessellation shader, mesh shader or trace the heightmap in a frament shader with parallax mapping. In constrast, the vulkan raytracing API would normally only take regular triangle geometry. A base mesh would need to be tessellated and displaced before building the acceleration structure. This limitation is noted by ¹, in which heightmap displacement traced directly using min-max mipmap acceleration similarly to ² and ³. An alternative to tessellating geometry is NVIDIA Micro-Mesh. This GPU feature offers a way to apply displacement without tessellating in the application code. The vulkan raytracing acceleration structure build step is also faster when using Micro-Mesh. However, building the Micro-Map that holds the displacement is not trivial to code. The heightmap_rtx library simplifies that step, taking just a VkImage displacement image and converting it before the acceleration structure build.

Limitations

There are a number of limitations of heightmap_rtx when used for displacement. Please see the README in its repository for details. A significant one with regard to correctness is that direction vectors are not normalized after interpolation. This means displacement near high base mesh curvature will produce quite different results.

Footnotes

1. Theo Thonat, Francois Beaune, Xin Sun, Nathan Carr, and Tamy Boubekeur. 2021. Tessellation-free displacement mapping for ray tracing. ACM Trans. Graph. 40, 6, Article 282 (December 2021)
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2. Kyoungsu Oh, Hyunwoo Ki, and Cheol-Hi Lee. 2006. Pyramidal displacement mapping: a GPU based artifacts-free ray tracing through an image pyramid. In Proceedings of the ACM symposium on Virtual reality software and technology (VRST '06)
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3. Art Tevs, Ivo Ihrke, and Hans-Peter Seidel. 2008. Maximum mipmaps for fast, accurate, and scalable dynamic height field rendering. In Proceedings of the 2008 symposium on Interactive 3D graphics and games (I3D '08)
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