Raymarching & SDF Modeling
Before diving into Chisel, it helps to understand the technology behind it.
What is a Signed Distance Field?
A Signed Distance Field (SDF) defines a shape by calculating the shortest distance from any point in space to the surface. Points outside the shape have positive distance, points inside have negative distance, and the surface itself is where the distance equals zero.
Instead of storing vertices, edges, and faces like traditional meshes, an SDF stores a mathematical function. This means:
- Infinite resolution - No faceting, surfaces are mathematically smooth
- Perfect booleans - Combining shapes is a simple math operation
- Smooth blending - Fillets between shapes come naturally from the math
- No topology issues - No n-gons, non-manifold edges, or bad normals
What is Raymarching?
Raymarching is a rendering technique that visualizes SDF shapes. For each pixel on screen, a ray is cast from the camera into the scene. The ray “marches” forward in steps - at each step, the SDF tells it how far the nearest surface is, so it can safely jump that distance without missing anything.
When a ray gets close enough to a surface (within the hit threshold), it stops and that pixel is shaded. This is how Chisel’s built-in renderer displays your SDF models in real-time.
How it Differs from Other Renderers
| Rasterization (EEVEE) | Ray Tracing (Cycles) | Ray Marching (Chisel) | |
|---|---|---|---|
| Input | Triangles | Triangles | Distance Functions |
| Precision | Limited by mesh density | Limited by mesh density | Mathematically exact |
| Booleans | Mesh operations | Mesh operations | Math operations |
| Speed | Very fast | Slow | Real-time for SDF |
Why SDF Modeling?
Advantages
- Rapid iteration - Add, subtract, blend shapes instantly without topology concerns
- Smooth fillets - Adjustable blend radius on any boolean operation
- Edge rounding - Per-primitive rounding with multiple profile types
- Clean conversion - Convert to mesh only when you need to, with multiple algorithms
Limitations
- No UV painting - SDF shapes don’t have UVs until converted to mesh
- GPU dependent - Ray-marching renderer requires decent GPU
- Scene complexity - Very complex scenes may slow the viewport
- Export requires conversion - Must convert to mesh for use outside Chisel
How Chisel Uses SDF
In Chisel, every primitive you create (Box, Sphere, Cylinder, etc.) is defined as an SDF function. When you:
- Add a primitive: Creates a distance function for that shape
- Add a boolean modifier: Combines distance functions (min, max operations)
- Adjust blend radius: Smoothly interpolates between distance functions
- View in the viewport: The ray-marching renderer evaluates all distance functions per pixel
- Convert to mesh: An algorithm samples the distance field to extract a polygon surface
This means you work with perfectly smooth, resolution-independent shapes throughout your modeling process, and only commit to a mesh resolution at the very end.
Next Steps
Ready to start? Head to the Installation guide.