Distance fields & volumes
Two ways to describe solid shape in 3D: a live "how far am I from the surface" formula, or that formula baked into a grid of voxels you can light like smoke.
Distance fields
A Distance Field answers one question at every point in space: how far am I from the nearest surface? Inside the shape the answer is negative, on the surface it is zero, outside it is positive.
Because it is evaluated rather than stored, a distance field stays exact at any zoom, and two fields can be combined with smooth booleans. They melt into each other, carve holes, or round their seams.
A Distance Field is a kind of Fields. Several things become one:
Analytic shapes. Spheres, boxes, cylinders, tori and cones have closed-form distance functions, so they stay exact at any scale. See the Analytical toggle and the per-row
@analyticattribute in Analytic shapes.A mesh, measured as distance to the model's surface.
An image. A logo or mask becomes a distance field from its edges, which is what outlines and glows read from.
Points. A cloud of points blobs together into one smooth surface, like droplets merging.
Use a distance field wherever shapes need to interact: soft unions, smooth subtraction, thickening, shells.
Volumes
A Volume is a fixed 3D grid of voxels, each holding one value. Resolution is set at bake time.
Bake a Distance Field into a Volume to freeze it onto a grid, or fill a Volume directly with density, the cloudy material that smoke and clouds are made of. Volumes are how soft, lit, atmospheric things render: smoke, fog, clouds, glowing energy.
The look of a Volume comes from its material: colour, how much light it scatters and absorbs, a Gradient mapping density to colour, and fine detail for wispy edges. The renderer adds self-shadowing, soft glow and rim scattering.
Mesh Mode on Volume Render decides which of the two a solid source becomes. SDF voxelises it as a signed distance field, which is what surface rendering and collisions want. Density fills a 0 to 1 occupancy grid instead, and that is the one to blur, advect and run reaction-diffusion over. The mechanism follows the source either way: a mesh voxelises, points splat, and Kernel Type shapes each point's falloff as a smooth Gaussian, a Linear cone, or a hard Constant sphere.
A single-channel Volume holds either distance or density, and the two are stored identically. Which reading applies is authored on Volume Render's Display Mode: Volumetric renders the grid as fog, Surface sphere-traces the distance isosurface as a lit solid. Volumetric is the default. In Surface mode a Shade Smooth toggle appears, on by default, which smooths the traced normals so the grid's own voxel facets stop showing through.
Converting between them
One is the live formula, the other the baked grid. Meshes complete the trio as solid surfaces you can sculpt and shade.
Distance Field → Volume. Bake the formula onto a grid to render it as lit fog or a shaded surface, or to feed it into volume effects.
Volume → Distance Field. Read the distance to where the volume crosses its surface. The inserted conversion defaults to a fast
jfapass, which is blocky at voxel scale. Set itsalgorithmtomesh_distancefor a sub-voxel surface at more cost.Mesh → Distance Field. Measure distance to a model's surface so it can be thickened, shelled, or booleaned smoothly.
Distance Field / Volume → Mesh. Extract a watertight surface from the field, turning blended organic shape back into editable geometry.
Connecting a sphere to a Volume node, or a mesh to an effect that expects a field, inserts the conversion automatically.
A bigger grid holds more detail and costs more memory. Memory scales with the cube of resolution: 512³ holds eight times the voxels of 256³. Start coarse and raise resolution once the look is right.