homogeneous_medium: Homogeneous Participating Medium

In rayrender: Build and Raytrace 3D Scenes

Homogeneous Participating Medium

Description

Describe a medium independently of the surface that contains it. Attach it to closed objects with [set_medium()]. Rendering automatically selects integrator_type = "nee" for scenes containing attached media.

Usage

homogeneous_medium(
  sigma_a = 0,
  sigma_s = 1,
  density_scale = 1,
  g = 0,
  emission = 0,
  temperature = NULL,
  emission_scale = 1,
  temperature_scale = 1,
  temperature_offset = 0,
  medium_transform = diag(4),
  haze = TRUE,
  haze_density_threshold = NULL
)

Arguments

sigma_a	Default '0'. Absorption coefficient, a nonnegative number or RGB vector, per world-space distance unit.
sigma_s	Default '1'. Scattering coefficient, a nonnegative number or RGB vector, per world-space distance unit.
density_scale	Default '1'. Nonnegative multiplier for both coefficients.
g	Default '0'. Henyey-Greenstein asymmetry, strictly between -1 and 1. Positive values scatter forward along the incident light direction.
emission	Default '0'. Nonnegative scalar or RGB emitted radiance 'Le'. Color names are also accepted. The volume source is 'sigma_a * Le'.
temperature	Default 'NULL'. Blackbody temperature in kelvin. Mutually exclusive with nonzero 'emission'.
emission_scale	Default '1'. Nonnegative multiplier for emitted radiance.
temperature_scale	Default '1'. Nonnegative multiplier applied after subtracting 'temperature_offset' from the temperature.
temperature_offset	Default '0'. Offset subtracted from temperatures.
medium_transform	Default 'diag(4)'. Invertible affine matrix mapping medium coordinates into the containing object's local coordinates.
haze	Default 'TRUE'. Include clear-air atmospheric haze inside this medium when enabled by [sky_light()], subject to 'haze_density_threshold'. Set 'FALSE' to skip its atmospheric in-scattering and extinction throughout the entire boundary, including empty cells, regardless of the threshold. The medium's own scattering, absorption, and emission remain active. In nested media the innermost medium's setting applies; 'sky_light(haze_in_volumes = FALSE)' overrides all media. This is an approximation and may affect thin clouds, edges, or low-altitude haze.
haze_density_threshold	Default 'NULL'. With 'haze = TRUE', omit haze only where interpolated density times 'density_scale' is at least this positive number. Lower-density regions and empty space retain haze. A homogeneous medium has density one before scaling. 'NULL' includes haze throughout the boundary. Ignored with 'haze = FALSE' or global haze exclusion. The threshold measures density, not optical depth or scattering strength; choose which media to tag accordingly. Crossings follow the trilinear field, including between scattering events, and transform with the medium.

Value

A reusable 'ray_medium' description.

Examples

fog = homogeneous_medium(sigma_s = 5, g = 0.65)
scene = set_medium(cube(width=1.2), fog) |>
add_object(sphere(y=1,x=1,radius=0.3,material=light(intensity=20))) |>
add_object(generate_studio(material=diffuse(color="dodgerblue")	))
render_scene(scene, integrator_type = "nee", sample_method="sobol")

# Foggy cornell box
fog = homogeneous_medium(sigma_s = 0.1, sigma_a = 0.1, g = 0, density_scale = 0.01, temperature = 0)
 scene = generate_cornell(
 lightwidth = 10,
 lightdepth = 10,
 lightintensity = 3000
) |>
 add_object(set_medium(
   cube(x = 555 / 2, y = 555 / 2, z = 555 / 2, width = 554),
   fog
 ))
render_scene(
 scene,
 integrator_type = "nee",
 fov = 40,
 samples = 256
)

rayrender documentation built on Sept. 16, 2026, 9:08 a.m.