Raymarch Bevy

Rust

Bevy

A ray-marching renderer built in Rust using Bevy and WGSL shaders. A custom fullscreen shader is used to replace the camera with an in-shader camera that performs ray marching to display the scene. Integrated with eGUI to allow for real-time modification of parameters at runtime.

Project Summary

Built a real-time ray-marched 3D scene renderer using a fullscreen shader pipeline in Bevy.
Implemented responsive rendering that compensates for window rescaling to remove texture stretching.
Created a fly camera system which pans via mouse input, translates based on keyboard inputs, and includes sprint controls for faster movement.
Designed a modular shape system built using Signed Distance Functions, currently implemented for spheres, cubes, and planes.
Added smooth unions or boolean blending for combining SDFs, with configurable blending constants.
Implemented dynamic lighting, surface shading, and gamma correction in the fragment shader, consistent with the Phong shading model.
Built a custom ray-march loop with collision detection, outlines for near-misses, and a gradient sky background.
Structured shader data using Rust-side materials passed directly into WGSL uniforms.
Included development-build eGUI tooling to modify in-game data in real-time.

Technical Challenges

Balancing of ray-march step count against rendering performance.
Maintaining visual quality while avoiding excessive shader calculations.
Preventing stretched output across varying window aspect ratios.
Ensuring stable camera controls with smooth rotation, while avoiding gimbal locking issues.
Passing structured data from Rust into the shader efficiently using uniforms, including dynamic shape data arrays.

Rendering Pipeline

A fullscreen quad rendered each frame.
Fragment shader casts a ray from the camera for each pixel.
Ray marches through the scene using Signed Distance Functions.
Closest hit point is shaded using normals and lighting, near-misses are highlighted and become outlines.

Shader Camera

Replaced the traditional in-engine camera with an in-shader camera.
Calculated a ray direction, per-pixel, using screen-space coordinates and the calculated view frustum (based on camera parameters).
Implemented free-fly movement with keyboard translation across forward, right, and up axes of the camera.
Added mouse-look controls to rotate camera smoothly in real-time.
Camera rotations are stored and modified as quaternions to avoid gimbal lock.
Passed camera position, rotation, FOV, and basis vectors from Rust into WGSL uniforms on each frame.
Included sprint movement for faster scene navigation (Controlled via Shift).
Integrated camera parameters with the eGUI windows to allow real-time modification while the scene is running.

Shape System

Scene geometry represented using modular Signed Distance Functions primitives.
Currently supports spheres, cubes, and planes.
New shapes can be added by implementing additional SDF definitions.
Each shape stores its position, scale, and colour, as well as its shape type (represented as an integer).
Shapes can be blended using smooth unions or combined using boolean operations.
Blending parameters are exposed at runtime and can be modified using the eGUI windows.

Lighting & Shading

Surface normals are approximated from neighbouring SDF samples.
Phong-style lighting model used for the diffuse and specular shading.
Single dynamic light source with configurable position and colour.
Gamma correction applied before final colour output for improved colour accuracy.
Background rendered as a sky gradient when the ray didn't collide with any geometry.
Silhouette outlines are generated from near-miss ray distances.
Hard shadows are calculated to darken areas where the shapes block the light from the light source.

Future Improvements

Portal rendering using non-linear ray traversal through SDF space.
Soft shadows, and ambient occlusion to improve realism of the rendering.
Multi-light support with extended material properties (roughness, emissiveness, etc).
Adaptive ray-march step optimisation based on scene complexity.
Additional SDF primitives: cylinders, capsules, and toruses.