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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.