Getting Started with scimesh

What is scimesh?

scimesh is a fast, headless, GPU-free software renderer for 3D triangle meshes that produces publication-quality images for papers, slides, and presentations. It works anywhere R works — no X11, no OpenGL, no GPU required.

Applications span any field that works with 3D surfaces: - Neuroimaging: cortical surface visualisation (FreeSurfer data) - Structural biology: molecule surfaces from PDB files - Computer graphics: Stanford models, procedural geometry, textured meshes - Engineering and simulation: mesh-based scientific visualisation of any kind

All rendering is done in modern C++17 and returns in-memory RGBA images that can be saved to PNG or composed into multi-panel figures.

While scimesh can serve as a drop-in renderer backend when rgl/OpenGL is unavailable (e.g., on macOS without XQuartz, on HPC clusters, in CI containers), it is a general-purpose visualisation tool — not tied to any specific domain or package.

Installation

# Install from GitHub
remotes::install_github("dfsp-spirit/scimesh")

For the full viridis colormap family (magma, inferno, cividis, etc.), you may optionally install viridisLite:

install.packages("viridisLite")

But this is not required — scimesh ships built-in viridis_colormap() and diverging_colormap() functions that use only base R.

Quick Start

library(scimesh)

sphere <- generate_sphere(c(0, 0, 0), radius = 1.2,
                          segments = 32, color = c(0.9, 0.3, 0.2, 1.0))
cam <- camera_auto(sphere, direction = c(1.2, 0.8, 1))

# Flat-shaded sphere
img <- render_mesh(sphere$vertices, sphere$triangles,
    colors = sphere$colors, camera = cam,
    options = render_options(
        lights = list(
            list(position = c(0.5, 1.0, 0.8), intensity = 1.5),
            list(position = c(-0.5, 0.2, 0.6), intensity = 0.5))))

tmp_file <- tempfile(fileext = ".png")
write_png(img, tmp_file)
printf("Rendered sphere written to: %s\n", tmp_file)

Rendering Features

Render Options Reference

All rendering is controlled via render_options(). The following parameters are available:

Parameter	Type	Default	Description
`width`, `height`	integer	800, 600	Output image dimensions in pixels
`shading`	`"smooth"` / `"flat"`	`"smooth"`	Per-vertex (smooth) or per-face (flat) shading
`backface_culling`	logical	`TRUE`	Skip triangles facing away from camera
`background_color`	RGBA vector	`c(0,0,0,0)`	Transparent black by default
`default_color`	RGBA vector	`c(0.7,0.7,0.7,1)`	Fallback when no per-vertex colors
`invert_normals`	logical	`FALSE`	Flip face orientation
`wireframe`	logical	`FALSE`	Render edges only
`wireframe_color`	RGBA vector	`c(0,0,0,1)`	Edge color in wireframe mode
`projection`	`"perspective"` / `"orthographic"`	`"perspective"`	Camera projection type
`specular_color`	RGBA vector	`c(0,0,0,0)`	Specular highlight color (off by default)
`shininess`	numeric	0	Gloss tightness (8–128)
`ambient`	numeric	0.3	Ambient light level (0–1)
`contrast`	numeric	1.0	S-curve contrast multiplier
`lights`	list or `NULL`	`NULL`	Custom light list (auto-default if `NULL`)
`fog_enabled`	logical	`FALSE`	Enable depth fog
`fog_start`	numeric	0	Near-plane fog start
`fog_end`	numeric	1	Far-plane fog end
`fog_color`	RGBA vector	`c(0,0,0,0)`	Fog color
`aa_samples`	integer (1, 2, or 4)	1	Ordered-grid supersampling factor
`ssao_enabled`	logical	`FALSE`	Enable screen-space ambient occlusion
`ssao_radius`	numeric	16	SSAO sample radius in pixels
`ssao_intensity`	numeric	0.8	SSAO occlusion strength (0–1)
`threads`	integer	0	Number of CPU threads (0 = auto)
`clip_planes`	list or `NULL`	`NULL`	Custom clipping planes

The following sections cover the most important options in detail.

Lighting and Shading

scimesh uses a Blinn-Phong shading model with support for multiple light sources, specular highlights, ambient control, and contrast adjustments.

Ambient Lighting

The ambient parameter (default 0.3) controls how much light reaches surfaces that face away from the light source. Lower values produce deeper shadows and more contrast:

render_options(ambient = 0.15)  # deeper shadows

Multi-Light Setups

Explicit lights give you full control over direction, colour, and intensity:

render_options(
    ambient = 0.2,
    contrast = 1.1,
    lights = list(
        list(position = c(0.5, 1.0, 0.8), color = c(1, 0.97, 0.9, 1),
             intensity = 1.5),
        list(position = c(-0.5, 0.2, 0.6), color = c(0.4, 0.5, 0.8, 1),
             intensity = 0.5)))

Specular Highlights

Add a glossy sheen to surfaces:

render_options(
    specular_color = c(0.4, 0.4, 0.4, 1),  # white highlight
    shininess = 64)                          # tight spot

`shininess` value	Look
8–16	Soft plastic
32–64	Shiny surface
128	Glass-like tight spot

Contrast Adjustment

Pass contrast to render_options() to apply an S-curve contrast stretch after shading. Values > 1.0 push darks toward black and lights toward white, increasing perceived contrast. The default 1.0 means no change:

render_options(contrast = 1.1)  # subtle S-curve

The formula applied is (value - 0.5) * contrast + 0.5, clamped to [0, 1]. Typical values are 1.1–1.2 for a gentle boost, or up to 1.5 for a dramatic look.

You can also apply contrast as post-processing to an existing image:

img <- render_mesh(mesh$vertices, mesh$triangles)
img <- image_apply_contrast(img, contrast = 1.1)
tmp_file <- tempfile(fileext = ".png")
write_png(img, tmp_file)
printf("Contrast-adjusted image written to: %s\n", tmp_file)

Camera

Auto-Framing

camera_auto() computes a camera that fits any mesh or vertex set:

verts <- matrix(rnorm(900), ncol = 3)
cam <- camera_auto(verts, direction = c(1, 1, 1), fov = 45)

It accepts either an Nx3 matrix or a mesh descriptor list.

Manual Camera

For full control, use camera():

cam <- camera(eye = c(0, 0, 10), center = c(0, 0, 0),
              up = c(0, 1, 0), fov = 30)

Orbiting the Camera

camera_orbit() rotates a camera’s eye and up vector around its center by a given angle about an axis. This is useful for generating turntable-style frame sequences:

cam <- camera_auto(mesh, direction = c(1, 1, 1))

for (i in seq_len(8)) {
    cam_i <- camera_orbit(cam, angle_degrees = 360 / 8 * (i - 1))
    img   <- render_mesh(mesh$vertices, mesh$triangles, camera = cam_i,
                         options = render_options(width = 600, height = 400))

    # Construct the file path inside tempdir()
    file_name <- sprintf("frame_%04d.png", i - 1)
    file_path <- file.path(tempdir(), file_name)

    # Write the image to the temporary directory
    write_png(img, file_path)
}

message("Frames saved in: ", tempdir())

For more complex trajectories, replace camera_orbit() with your own function — it only needs to set camera$eye and camera$up.

The resulting PNG frames can be assembled into a video with ffmpeg or into an animated GIF with your tool of choice. See examples/R/video_frames_orbit/ for a runnable R example, and examples/cpp/brain_video/ for a C++ version that renders 48 full-brain frames.

rgl-Compatible Default View

camera_auto() accepts an rgl_compat parameter. When TRUE, it mimics rgl’s default view parameters:

Parameter	scimesh default	`rgl_compat = TRUE`
FOV	45°	30°
Elevation	0° (front-on)	15° above horizon
Distance basis	bounding box	bounding sphere

The distance formula follows rgl’s implementation exactly: distance = sphere_radius / sin(FOV / 2), where sphere_radius is half the length of the axis-aligned bounding box diagonal.

mesh <- generate_cuboid(c(0, 0, 0), c(1, 1, 1))

# scimesh default: straight front view
img_default <- render_mesh(mesh)

# rgl-compatible view: elevated, matching rgl's default look
cam <- camera_auto(mesh, rgl_compat = TRUE)
img_rgl   <- render_mesh(mesh, camera = cam)

This is especially useful when comparing outputs between scimesh and rgl, or when you prefer rgl’s slightly elevated default perspective.

Projection Type

Perspective (default) or orthographic (parallel projection, matching rgl’s view3d(fov = 0) convention):

render_options(projection = "orthographic")

Anti-Aliasing

scimesh supports ordered-grid supersampling (SSAA). Pass aa_samples = 2L for 2x2 SSAA (renders internally at double resolution, downsamples by box averaging):

render_options(aa_samples = 2L)

Values of 1 (off), 2, or 4 are supported. Higher values give smoother edges but use proportionally more memory and time.

Wireframe Mode

render_options(wireframe = TRUE,
    wireframe_color = c(0, 0, 0, 1))  # black edges

Edges are computed via barycentric distance testing inside the triangle rasterizer — no separate line primitives needed. Edge thickness adapts to triangle size so small triangles don’t disappear.

Screen-Space Ambient Occlusion (SSAO)

SSAO adds contact shadows in crevices and concavities, dramatically improving depth perception and realism. It’s a screen-space post-processing effect — no extra geometry needed:

render_options(
    ssao_enabled = TRUE,
    ssao_radius = 12,       # sample radius in pixels
    ssao_intensity = 0.5)   # occlusion strength (0–1)

Higher ssao_radius values sample a larger area (more expensive but softer shadows). Higher ssao_intensity darkens occluded regions more. Typical settings: radius 8–16, intensity 0.4–0.8.

SSAO is demonstrated in the spot_cow and dragon R examples, and extensively in the C++ examples.

Depth Fog

Atmospheric depth fog fades distant geometry toward a background color, useful for emphasising foreground objects or creating stylised renders:

render_options(
    fog_enabled = TRUE,
    fog_start = 0.6,              # begin fade at 60 % depth
    fog_end = 1.0,                # fully fogged at far plane
    fog_color = c(0.9, 0.95, 1, 1))  # pale blue fog

Fog is applied linearly between fog_start and fog_end in normalised device coordinates.

Semi-Transparent Overlays

scimesh supports proper alpha blending with depth-sorted back-to-front rendering. This is useful for visualising nested surfaces (e.g., white matter and pial surface in neuroimaging), or for glass-brain effects.

R example:

library(scimesh)

white <- freesurferformats::read.fs.surface("sub-01/surf/lh.white")
pial  <- freesurferformats::read.fs.surface("sub-01/surf/lh.pial")

nv <- nrow(white$vertices)

white_mesh <- list(
    vertices  = white$vertices,
    triangles = white$faces,
    colors    = matrix(c(0.7, 0.7, 0.7, 1.0), nv, 4, byrow = TRUE))

pial_mesh <- list(
    vertices  = pial$vertices,
    triangles = pial$faces,
    colors    = matrix(c(0.9, 0.3, 0.2, 0.35), nv, 4, byrow = TRUE))

cam <- camera_auto(pial_mesh, direction = c(-1, 0, 0.2))
img <- render_scene(list(white_mesh, pial_mesh), cam,
    render_options(width = 1200, height = 900,
        backface_culling = FALSE,
        specular_color = c(0.4, 0.4, 0.4, 1),
        shininess = 64))
temp_file <- tempfile(fileext = ".png")
write_png(img, temp_file)
printf("Transparent render written to: %s\n", temp_file)

C++ example: See examples/cpp/transparency/ in the repository.

Background and Transparency

By default, scimesh renders with a transparent background (background_color = c(0, 0, 0, 0)), which is ideal for compositing.

For a solid background (e.g., white for papers), set:

render_options(background_color = c(1, 1, 1, 1))  # solid white

The background color is written to the output image’s alpha channel, so transparent backgrounds survive PNG export and can be further composited in tools like ImageMagick or layout packages.

Working with Meshes

Procedural Geometry

scimesh provides C++ and R functions for generating primitive geometry:

cube    <- generate_cuboid(c(0, 0, 0), c(1, 1, 1), c(1, 0, 0, 1))
sphere  <- generate_sphere(c(0, 0, 0), radius = 1.2,
                           segments = 32, color = c(0.9, 0.3, 0.2, 1))
cyl     <- generate_cylinder(c(0, -1, 0), c(0, 1, 0), 0.5, 32,
                             c(0.1, 0.7, 0.3, 1))
cone    <- generate_cone(c(0, -1.2, 0), c(0, 1.2, 0), 0.6, 32,
                         c(0.9, 0.7, 0.1, 1))
pyramid <- generate_pyramid(c(0, 0, 0), c(0, 1.5, 0), 1,
                            c(0.7, 0.2, 0.8, 1))
tetra   <- generate_tetrahedron(c(-1, -0.5, -1), c(1, -0.5, -1),
            c(0, -0.5, 1), c(0, 1.2, 0), c(0.2, 0.8, 0.8, 1))
torus   <- generate_torus(c(0, 0, 0), 1.0, 0.35, 24, 12,
                          c(0.6, 0.4, 0.2, 1))
plane   <- generate_plane(c(0, 0, 0), c(0, 1, 0), 1.2, 0.8,
                          c(0.5, 0.5, 0.5, 1))

See examples/R/primitives/run.R for a gallery script that renders all primitives side-by-side in both shaded and wireframe mode.

Mesh I/O

scimesh can read and write standard 3D mesh file formats. All readers return a mesh descriptor list with vertices, triangles, and optionally normals, uv, or colors.

# Read a Wavefront OBJ file (with optional UVs and normals)
mesh <- read_obj("model.obj")

# Read a Stanford PLY file (with optional vertex colors)
mesh <- read_ply("model.ply")

# Read an STL file (binary or ASCII)
mesh <- read_stl("model.stl")

# Write a mesh to STL
tmp_file1 <- tempfile(fileext = ".stl")
tmp_file2 <- tempfile(fileext = ".stl")

write_stl(mesh, tmp_file1)               # binary (default)
write_stl(mesh, tmp_file2, format = "ascii")

The OBJ reader supports multi-shape files and texture coordinates. The PLY reader supports per-vertex RGB colors. STL writes preserve vertex normals when available.

Mesh Transforms

Translate, scale, rotate, or apply arbitrary 4x4 matrices to meshes:

mesh <- generate_cuboid(c(0, 0, 0), c(1, 1, 1), c(1, 0, 0, 1))
mesh <- translate_mesh(mesh, c(5, 0, 0))
mesh <- scale_mesh(mesh, 2.0)
mesh <- rotate_mesh(mesh, pi / 4, c(0, 0, 1))
mesh <- transform_mesh(mesh, my_4x4_matrix)

Face Colors

Per-face coloring lets you assign a single color to every vertex of a triangle. This is useful for parcellation overlays or material assignment:

mesh <- generate_cuboid(c(0, 0, 0), c(1, 1, 1))

# 12 triangles, each gets a color
fc <- matrix(c(1, 0, 0, 1), nrow = 12, ncol = 4, byrow = TRUE)
img <- render_mesh(mesh$vertices, mesh$triangles, face_colors = fc)

When face_colors is provided, it takes precedence over vertex colors.

Texture Mapping

Load a texture image and assign UV coordinates to render textured meshes:

# Requires the 'png' package
library(png)
tex <- readPNG("texture.png")

# UV coordinates (Nx2, values 0-1) must match vertex order
mesh <- read_obj("textured.obj")  # OBJ reader extracts UVs

img <- render_mesh(mesh$vertices, mesh$triangles,
    uv = mesh$uv, texture = tex)

Bilinear texture sampling is used for smooth results.

Mesh Utilities

Bounding Box

Compute or visualise the axis-aligned bounding box:

mesh <- generate_torus(c(0, 0, 0), 1.5, 0.4, 32, 16)
bbox <- mesh_bbox(mesh)
bbox$min  # c(xmin, ymin, zmin)
bbox$max  # c(xmax, ymax, zmax)

# Generate a wireframe bounding box mesh for rendering
bbox_mesh <- generate_bbox(mesh, color = c(0, 0, 0, 1), radius = 0.02)

Axis Arrows

Generate coloured XYZ axis arrows (red X, green Y, blue Z):

axes_mesh <- generate_axes(center = c(0, 0, 0), size = 2)
# Render together with your mesh:
img <- render_scene(list(mesh, axes_mesh), cam)

Lower-Level Rendering

Beyond render_mesh() and render_scene(), scimesh provides lower-level functions for special use cases.

Raw Triangles (no index buffer)

Render geometry where positions and colors are flat arrays with 3 vertices per triangle — useful for dynamically generated geometry:

positions <- matrix(c(0,0,0, 1,0,0, 0.5,1,0,
                      0,0,1, 1,0,1, 0.5,1,1), ncol = 3, byrow = TRUE)
colors <- matrix(c(1,0,0,1, 0,1,0,1, 0,0,1,1,
                   1,1,0,1, 0,1,1,1, 1,0,1,1), ncol = 4, byrow = TRUE)
cam <- camera_auto(positions)
img <- render_triangles(positions, colors, cam)

Points

Render point cloud data with depth-tested circular markers:

pts <- matrix(rnorm(300), ncol = 3)
cols <- matrix(c(1, 0.5, 0, 1), nrow = nrow(pts), ncol = 4, byrow = TRUE)
img <- render_points(pts, cols, radius = 4)

Lines (as Cylinders)

Render line segments as thin cylinders:

from <- matrix(c(0,0,0, 0,0,0), ncol = 3, byrow = TRUE)
to   <- matrix(c(1,0,0, 0,1,0), ncol = 3, byrow = TRUE)
cols <- matrix(c(1,0,0,1, 0,1,0,1), ncol = 4, byrow = TRUE)
img <- render_lines(from, to, radii = 0.05, colors = cols, cam)

Image Utilities

Colour Bars

scimesh can produce horizontal or vertical colour bars in pure R (no X11), ready to be composed alongside rendered images:

cbar <- colorbar_horizontal(viridis_colormap,
    n_colors = 256, width = 600, height = 80,
    ticks = c(0, 0.5, 1),
    tick_labels = c("min", "mid", "max"),
    title = "Value")

Both colorbar_horizontal() and colorbar_vertical() accept any colormap, specified either as: - A function returning hex colors (e.g., viridis_colormap, diverging_colormap, grDevices::hcl.colors, or viridisLite::viridis) - A vector of color strings (e.g., c("red", "white", "blue"))

Built-in colormaps (no extra packages required):

# Viridis (perceptually uniform, colourblind-friendly)
viridis_colormap(256)

# Blue-white-red diverging (for signed data like Z-scores)
diverging_colormap(256)

# Any base R palette via wrapper functions
my_cmap <- function(n) grDevices::hcl.colors(n, palette = "inferno")
cbar <- colorbar_horizontal(my_cmap)

# Or pass colors directly
cbar <- colorbar_horizontal(c("darkblue", "cyan", "yellow", "red"))

If you have viridisLite installed, you can use its full colormap family (magma, inferno, plasma, cividis) directly:

library(viridisLite)
cbar <- colorbar_horizontal(viridis)  # viridisLite function

See examples/R/colormaps/run.R for a complete demonstration.

Compositing Multiple Images

compose_layout() arranges rendered images in a grid with optional per-row/per-column cropping to eliminate wasted whitespace:

img1 <- render_mesh(...)
img2 <- render_mesh(...)
result <- compose_layout(list(img1, img2), nrow = 1L, crop = TRUE)
tmp_file <- tempfile(fileext = ".png")
write_png(result, tmp_file)
printf("Composed image written to: %s\n", tmp_file)

Image Stacking

Quick helpers for combining images:

# Horizontal stack (side by side)
result <- stack_horizontal(img1, img2, img3)

# Vertical stack (one below another)
result <- stack_vertical(img1, img2)

# With a colorbar
result <- stack_horizontal(img1, img2,
    colorbar = colorbar_horizontal(viridis_colormap))

Interoperability with Other Packages

rgl / tmesh3d

scimesh and rgl mesh formats can be converted in both directions, and scimesh render functions accept rgl meshes transparently — no manual conversion needed.

Rendering an rgl mesh directly

Pass an rgl tmesh3d object (or any list with vb and it components) directly to render_mesh() or include it in a scene list for render_scene() — the conversion happens automatically:

if (requireNamespace("rgl", quietly = TRUE)) {
    rgl_mesh <- rgl::tetrahedron3d()
    img <- render_mesh(rgl_mesh)          # transparent conversion
}

This also works when mixing scimesh and rgl meshes in a scene:

cube <- generate_cuboid(c(-1, 0, 0), c(0.5, 0.5, 0.5))
img <- render_scene(list(cube, rgl_mesh), cam)   # mixed formats

rgl → scimesh (explicit)

If you prefer explicit conversion, use mesh_from_rgl(). This also works without the rgl package installed — any list with vb and it components is accepted:

tmesh <- list(
    vb = rbind(c(-1, -1, 1, 1), c(-1, 1, 1, -1), c(0, 0, 0, 0), c(1, 1, 1, 1)),
    it = rbind(c(1L, 1L), c(2L, 3L), c(3L, 4L)))
mesh <- mesh_from_rgl(tmesh)
img  <- render_mesh(mesh)

scimesh → rgl (inverse)

Convert a scimesh mesh back to rgl’s tmesh3d format with mesh_to_rgl(). Vertex colors are forwarded automatically if present in the mesh:

mesh <- generate_cuboid(c(0, 0, 0), c(1, 1, 1), color = c(1, 0, 0, 1))
rgl_mesh <- mesh_to_rgl(mesh)
if (requireNamespace("rgl", quietly = TRUE)) {
    rgl::shade3d(rgl::tmesh3d(
        vertices = rgl_mesh$vb,
        indices  = rgl_mesh$it), col = "red")
}

The returned list has vb (4×N homogeneous coordinates), it (3×M index matrix), and optionally normals and mat (material/colors).

Matching rgl’s Default View

When rendering an rgl mesh with scimesh, you may want the output to visually match what you’d see in an rgl window. Pass rgl_compat = TRUE to camera_auto() to get rgl’s default 30° FOV, 15° elevation, and bounding-sphere distance:

if (requireNamespace("rgl", quietly = TRUE)) {
    rgl_mesh <- rgl::cube3d()             # rgl primitive
    cam <- camera_auto(rgl_mesh, rgl_compat = TRUE)
    img <- render_mesh(rgl_mesh, camera = cam)
    write_png(img, "cube_rgl_view.png")
}

The rgl_compat camera uses the same algorithm rgl uses internally: it computes the bounding sphere (half-diagonal of the AABB) and places the eye at distance = sphere_radius / sin(FOV / 2) along a direction tilted 15° above the −Z axis.

Rvcg, Morpho, fsbrain, and other packages

The rgl mesh3d/tmesh3d format is the lingua franca for 3D meshes in R. Packages like Rvcg (mesh processing via VCGLIB), Morpho (geometric morphometrics), and fsbrain (neuroimaging) all produce and consume rgl-format meshes. Since scimesh transparently accepts rgl meshes, you can process a mesh with any of these packages and render it with scimesh without any conversion step:

if (requireNamespace("Rvcg", quietly = TRUE)) {
    mesh <- Rvcg::vcgSphere()          # returns rgl-format mesh
    img  <- render_mesh(mesh)          # scimesh renders it directly
}

Examples

The repository includes runnable R example scripts in examples/R/:

Example	What it shows
`spot_cow/run.R`	Textured OBJ mesh with multi-light setup and SSAO
`dragon/run.R`	Stanford Dragon with specular highlights and 4x AA
`primitives/run.R`	All procedural primitives in shaded + wireframe gallery
`transparency/run.R`	Semi-transparent pial overlay on white matter
`whole_brain_sulc/run.R`	Whole-brain sulcal depth with cortex masking
`video_frames_orbit/run.R`	Turntable orbit frame sequence
`colormaps/run.R`	Custom colormaps with colorbars

Run all examples at once:

cd examples/R
bash run_all_R.sh

For C++ examples, see examples/cpp/ and docs/CPP_GETTING_STARTED.md.

FAQ

How fast is it? A typical cortical surface (~300k triangles) at 1200x900 with 2x SSAA renders in 1–3 seconds on a modern CPU. Smaller meshes at lower resolution can render in 200 ms or less, depending on the CPU and number of lights.

Why is there no interactive 3D window in which I can rotate the mesh? scimesh is a headless (off-screen) renderer, also known as a software rasterizer. It produces images in roughly seconds, on just the CPU. For interactive rotation or real-time animation, you need to render at least 30 images per second. This is only achievable with a hardware renderer, i.e., a graphics card and the full software stack required to make use of it. If you have a graphics card, the typical solution in R is to use rgl/OpenGL for interactive visualization.

What about volume data, like 3D MRI scans in neuroimaging? scimesh renders 3D surface meshes. Volume slice visualisation (e.g., volvis.lb.with.surface() in fsbrain) is done entirely in R/magick without 3D rendering — it works independently of the renderer backend. Technically it’s just a 2D image, no renderer needed. This means you can use the functions in fsbrain for volume visualisation even if you do not have rgl/OpenGL, and are using scimesh for surface (mesh) rendering.

My images look pixelated / jagged — how do I fix this? Render at higher resolution, e.g. (render_options(width = 2560, height = 1440)), and enable anti-aliasing: render_options(aa_samples = 2L), or even higher like 4L.

How do I get a transparent background? This is the default (background_color = c(0, 0, 0, 0)). See the Background and Transparency section under Rendering Features.

How do I control the number of CPU threads? Set the threads option in render_options(). The default 0 automatically uses all available cores. Set to 1 for single-threaded rendering, or any positive integer to cap the thread count.

What affects render performance? The main factors are triangle count, output resolution (pixels), anti-aliasing level (aa_samples), number of lights, SSAO, and whether transparency sorting is needed. For largest meshes, the most effective optimisations are reducing aa_samples and output resolution. SSAO and multi-light setups each add roughly constant overhead per pixel.