Name: Mosaic
Author: Seveneves

Engine Features

Rendering, world generation, audio, and character systems.

Voxel Global Illumination

Real-time GI in a 256³ voxel volume using DDA ray marching. Hard and soft shadows via voxel tracing — no shadow maps. Per-vertex AO baked with DDA hemisphere tracing using Amanatides & Woo traversal.

Binary Greedy Meshing

Reduces triangle count 10-20x versus naive cubes. Multi-draw indirect rendering batches ~2,200 chunks into a single draw call. 4 LOD levels by distance with compute shader frustum culling on GPU.

Volumetric Lighting

God rays via a 3-pass pipeline: half-res DDA ray march, bilateral blur, and composite. Temporal dithering with Henyey-Greenstein phase function, adjustable 24-72 sample steps.

Water System

Heightfield rendering with pipe-model flow simulation. Ray-marched fullscreen water pass with wave animation, Fresnel reflections, refraction, and underwater fog.

Procedural Worlds

8 biomes (grasslands, desert, jungle, tundra, mountains, ocean, swamp, cavernous highlands) with 3D Perlin caves, ore veins, procedural trees, vegetation, and ruins. Region file persistence with zstd compression at 3:1 ratio.

Spatial Audio

3D positional audio with material-based sound categories. DDA raycast occlusion crossfades ambience between environments. Convolution reverb in caves, footstep material detection, and music system with crossfade transitions.

Character System

3rd-person camera with skeletal animation and FBX model loading via ufbx. Character customization for outfits, hair, and heads. Body part editor with bone-driven skinned meshes lit by the voxel GI system.

Post-Processing

Hybrid morphological-temporal AA with depth edge detection, pattern matching, temporal accumulation, and sharpening. Depth of field with near/far blur layers. Bloom, SSAO, and greedy-meshed voxel clouds with terrain shadows.

Under the Hood

Some of the implementation details.

Rendering Pipeline

Sky pass — procedural atmosphere
Opaque geometry — MDI mega-buffer batching
Characters — skinned meshes + voxel GI shadows
Water pass — ray-marched heightfield
SSAO — screen-space ambient occlusion
Volumetrics — DDA ray march + blur + composite
Post-process — DoF, AA, bloom
UI — hotbar, debug overlay, menus

Architecture

wgpu — Vulkan/DX12/Metal abstraction
19 WGSL shaders — compute + graphics
8 worker threads — generation, meshing, lighting
Lock-free channels — crossbeam MPSC queues
Region files — 32x32 chunk sectors, zstd compressed
SlotMap ECS — generational arena, O(1) lookup
Priority task system — player actions bypass gen queue
Criterion benchmarks — meshing, shadows, generation

What is Mosaic?

Mosaic is a voxel engine written from scratch in Rust and wgpu. Its rendering pipeline, world generation, meshing, lighting, audio, and ECS span approximately 32,000 lines of code.

The primary technical focus is real-time voxel global illumination: light is propagated through a 256³ voxel volume each frame using DDA ray marching, enabling hard and soft shadows without shadow maps. The engine is for graphics and game-engine developers exploring low-level rendering techniques.

The source is available on GitHub for inspection and building. It runs on Windows, macOS, and Linux via wgpu’s Vulkan, DirectX 12, and Metal backends.

How does Mosaic implement real-time global illumination?

Light propagation

DDA ray marching — Amanatides & Woo traversal steps through a 256³ voxel volume to trace rays from the sun and sky into the scene each frame
No shadow maps — hard and soft shadows are computed entirely by voxel ray tracing, avoiding the resolution and aliasing limitations of depth-map approaches
Per-vertex AO — ambient occlusion is baked per vertex at mesh-build time via DDA hemisphere tracing, then stored in the vertex buffer for zero runtime cost
GPU compute — shadow and AO passes run in WGSL compute shaders via wgpu; 8 background worker threads keep the GI volume in sync with player edits

Volumetric lighting

God rays — 3-pass pipeline: half-resolution DDA ray march into the GI volume, bilateral blur, then full-res composite
Phase function — Henyey-Greenstein scattering with 24–72 adjustable sample steps and temporal dithering to avoid banding
Greedy-meshed clouds — volumetric clouds are voxel geometry processed through the same greedy meshing pipeline as terrain, casting terrain shadows
Character integration — skinned mesh characters receive GI shadows from the voxel volume, so lighting is consistent between geometry types

What is Mosaic built with?

Core dependencies

wgpu — portable GPU abstraction targeting Vulkan, DirectX 12, and Metal from a single codebase
19 WGSL shaders — mix of compute and graphics passes; no third-party shader library
crossbeam — lock-free MPSC channels between 8 worker threads for generation, meshing, and lighting
SlotMap — generational arena backing the custom ECS; O(1) entity lookup with safe slot reuse
zstd — region file compression at a 3:1 ratio
ufbx — FBX loader for skeletal animation and character models

Architecture decisions

Custom engine systems — the ECS, renderer, and world systems are built specifically for Mosaic
Multi-draw indirect — ~2,200 chunks batched into a single GPU draw call via MDI mega-buffer; compute shader frustum culling on GPU
Binary greedy meshing — face-merging reduces triangle count 10–20× over naive cubes; 4 LOD levels by view distance
Priority task queue — player block edits bypass the generation queue so edits feel instant
Criterion benchmarks — meshing, shadow propagation, and world generation are all benchmarked; regressions surface before commit

More from Seveneves

Pixels

Pixel art toolkit and asset packs

Graal RC

Remote Control client for Graal Online

Research

Papers on mathematics and computation