Planetmap is a library for processing lazily evaluated radial functions with dynamic level-of-detail.

Planetmap is motivated by the desire to model to-scale planetary terrain in real time on commodity hardware. To accomplish this, it addresses multiple challenges:

• Dynamic level of detail
• Streaming larger-than-memory or procedural heightmap data
• Addressing the surface of the sphere without singularities
• Maintaining numerical stability over massive distances

This is accomplished by organizing data into a 6 virtual quadtrees, each corresponding to one face of a cubemap. Each node in a quadtree, referred to as a Chunk, can be associated with a square grid of height samples, each of which represents the altitude relative to sea level along a ray originating at the center of a planet. Streaming and level of detail can then be implemented with a CacheManager associated with GPU-resident buffers.

The transform of a Chunk relative to a camera can be computed on the CPU using double precision and then rounded to single precision. This allows for efficient processing on a commodity GPU while providing high precision for positions close to the camera, because while a Chunk may be distant enough from the center of the planet to produce jitter when naively rendered from a nearby camera, its distance to such a camera is small, and can hence be represented much more accurately.

Because every Chunk has a slightly different shape when mapped onto the surface of a sphere, to avoid discontinuities at LoD boundaries, and to reduce GPU memory and memory bandwith requirements, it is convenient to generate vertexes on-demand on the GPU based on heightmap data and Chunk coordinates. heightmap.glsl provides an example of this suitable for use in a vertex shader.

• ash exposes a wrapper around CacheManager that simplifies caching chunk data in Vulkan device-local memory based on a view transform, using the Vulkan bindings by the same name
• ncollide exposes helpers for nphysics-compatible collision detection against the surface of a radial heightmap
• simd exposes simdeez-based iterators for data-parallel computation of sample coordinates within a Chunk or chunk::Coord, useful for fast noise sampling

Planetmap includes a simple, unoptimized Vulkan demo that can be launched with cargo run --release --all-features --example demo. Use WASDRF and click-and-drag to move; velocity is proportional to altitude. For simplicity, it skips important optimizations such as generating and transferring chunks asynchronously in background threads, memoizing noise function samplings across height/color/normal map computation, and precomputing coarse octaves of the noise function used. The jittery performance which results can be avoided in a real application by not blocking frame rendering on chunk generation.