WhipperSnapPy

WhipperSnapPy is a Python/OpenGL tool to render triangular surface meshes with color overlays or parcellations and generate screenshots — from the command line, in Jupyter notebooks, or via a desktop GUI.

It works with FreeSurfer and FastSurfer brain surfaces as well as any triangle mesh in OFF, legacy ASCII VTK PolyData, ASCII PLY, or GIfTI (.gii, .surf.gii) format, or passed directly as a NumPy (vertices, faces) tuple.

Installation

pip install whippersnappy

For rotation video support (MP4/WebM — GIF works without this):

pip install 'whippersnappy[video]'

For the interactive desktop GUI:

pip install 'whippersnappy[gui]'

For interactive 3D in Jupyter notebooks:

pip install 'whippersnappy[notebook]'

Off-screen (headless) rendering on Linux is supported natively via OSMesa — no xvfb or GPU required. On Windows, GLFW creates an invisible window; a GPU driver is sufficient — no display needed. On macOS, a real display connection is required (NSGL does not support headless rendering). See the Docker guide for headless Linux usage.

Command-Line Usage

After installation the following commands are available:

Single-view snapshot (whippersnap1)

Renders one view of any triangular surface mesh:

whippersnap1 --mesh $SUBJECT_DIR/surf/lh.white \
             --overlay $LH_OVERLAY \
             --bg-map  $SUBJECT_DIR/surf/lh.curv \
             --roi     $SUBJECT_DIR/label/lh.cortex.label \
             --view left \
             -o snap1.png

# Also works with OFF / VTK / PLY / GIfTI and plain-text overlays
whippersnap1 --mesh mesh.off --overlay values.txt -o snap1.png
whippersnap1 --mesh surface.surf.gii --overlay overlay.func.gii -o snap1.png

Four-view snapshot (whippersnap4)

Renders lateral and medial views of both hemispheres into a single composed image:

whippersnap4 -lh $LH_OVERLAY \
             -rh $RH_OVERLAY \
             -sd $SUBJECT_DIR \
             --fmax 4 --fthresh 2 \
             --caption "Cortical Thickness" \
             -o snap4.png

Rotation video (whippersnap1 --rotate)

Renders a 360° animation of any triangular surface mesh. GIF output uses pure PIL (no extra install); MP4/WebM requires pip install 'whippersnappy[video]'.

whippersnap1 --mesh $SUBJECT_DIR/surf/lh.white \
             --overlay $LH_OVERLAY \
             --rotate \
             -o rotation.mp4

whippersnap1 --mesh $SUBJECT_DIR/surf/lh.white \
             --rotate \
             -o rotation.gif

Desktop GUI (whippersnap)

Launches an interactive Qt window with live threshold controls and mouse-driven rotation, pan, and zoom. Requires pip install 'whippersnappy[gui]'.

General mode — any triangular mesh:

whippersnap --mesh mesh.off --overlay values.txt
whippersnap --mesh lh.white --overlay lh.thickness --bg-map lh.curv

FreeSurfer shortcut — derive all paths from a subject directory:

whippersnap -sd $SUBJECT_DIR --hemi lh -lh $LH_OVERLAY
whippersnap -sd $SUBJECT_DIR --hemi rh --annot rh.aparc.annot

For all options run whippersnap1 --help, whippersnap4 --help, or whippersnap --help.

Python API

from whippersnappy import snap1, snap4, snap_rotate, ViewType, get_view_matrix
from whippersnappy import plot3d  # requires whippersnappy[notebook]

Function / Class	Description
snap1	Single-view snapshot of any triangular mesh → PIL Image
snap4	Four-view composed image (FreeSurfer subject, lateral/medial both hemispheres)
snap_rotate	360° rotation video of any triangular surface mesh (MP4, WebM, or GIF)
plot3d	Interactive 3D WebGL viewer for Jupyter notebooks
ViewType	Enum of camera presets used by snap1 and snap_rotate
get_view_matrix	Return the 4×4 view matrix for a ViewType preset

ViewType values — pass to the view parameter of snap1 or the start_view parameter of snap_rotate:

Value	Description
ViewType.LEFT	Left lateral view (default)
ViewType.RIGHT	Right lateral view
ViewType.FRONT	Frontal / anterior view
ViewType.BACK	Posterior view
ViewType.TOP	Superior / dorsal view
ViewType.BOTTOM	Inferior / ventral view

Both snap1 and snap_rotate also accept a raw 4×4 NumPy matrix for view / start_view. Use get_view_matrix to start from a preset and modify it:

import numpy as np
import pyrr
from whippersnappy import snap1, snap_rotate, ViewType, get_view_matrix

# Tilt the left-lateral preset slightly downward
mat = get_view_matrix(ViewType.LEFT).copy()
tilt = np.array(pyrr.Matrix44.from_x_rotation(np.radians(10)), dtype=np.float32)
mat = tilt @ mat

img = snap1('lh.white', overlay='lh.thickness', view=mat)
snap_rotate('lh.white', 'rotation.mp4', start_view=mat)

Supported mesh inputs (for snap1, snap_rotate, and plot3d): FreeSurfer binary surfaces (e.g. lh.white), OFF (.off), legacy ASCII VTK PolyData (.vtk), ASCII PLY (.ply), GIfTI surface (.gii, .surf.gii), or a (vertices, faces) NumPy array tuple.

Supported overlay / label inputs: FreeSurfer morph (.curv, .thickness), MGH/MGZ (.mgh, .mgz), plain text / CSV (.txt, .csv), NumPy (.npy, .npz), GIfTI functional/label (.func.gii, .label.gii).

Examples

from whippersnappy import snap1, snap4, ViewType

# FreeSurfer surface with overlay — default left lateral view
img = snap1('lh.white',
            overlay='lh.thickness',
            bg_map='lh.curv',
            roi='lh.cortex.label')
img.save('snap1.png')

# Specific view
img = snap1('lh.white', overlay='lh.thickness', view=ViewType.FRONT)
img.save('snap1_front.png')

# Four-view overview (FreeSurfer subject directory)
img = snap4(lh_overlay='/path/to/lh.thickness',
            rh_overlay='/path/to/rh.thickness',
            sdir='/path/to/subject',
            colorbar=True,
            caption='Cortical Thickness (mm)')
img.save('snap4.png')

# OFF / VTK / PLY / GIfTI mesh with a plain-text overlay
img = snap1('mesh.off', overlay='values.txt')
img = snap1('surface.surf.gii', overlay='overlay.func.gii')

# Array inputs (e.g. from LaPy or trimesh)
import numpy as np
v = np.array([[0,0,0],[1,0,0],[0,1,0],[0,0,1]], dtype=np.float32)
f = np.array([[0,2,1],[0,1,3],[0,3,2],[1,2,3]], dtype=np.uint32)
overlay = np.array([0.1, 0.5, 0.9, 0.3], dtype=np.float32)
img = snap1((v, f), overlay=overlay)

See tutorials/whippersnappy_tutorial.ipynb for complete notebook examples.

Docker

The Docker image provides a fully headless OSMesa rendering environment — no display server, xvfb, or GPU required. See DOCKER.md for details.

API Documentation

https://deep-mi.org/WhipperSnapPy

Links

Lab webpage: https://deep-mi.org