Custom Shaders

The svg3d shader API is designed to be easily extensible. The following example creates a RandomColorShader, which draws face colors at random from an input color map.

For this example, we will use the freud library to generate the Voronoi diagram of a set of random points in two dimensions, using an off-axis viewport to get a perspective image.

import freud
import numpy as np

import svg3d
from svg3d import get_lookat_matrix, get_projection_matrix

# Colors that will be randomly assigned to our polygons
cmap = [
    "#E9C99F", "#E7A27A", "#E57C62",
    "#BC6561", "#8E616C", "#6B5F76",
    "#48597A", "#13385A", "#031326"
]


class RandomColorShader(svg3d.shaders.Shader):
    def __init__(self, cmap=cmap, base_style=None, seed=0):
        super().__init__()
        self.rng = np.random.default_rng(seed=seed)
        self.cmap = cmap

    def __call__(self, face_index, mesh):
        base_style = self.base_style if self.base_style is not None else {}
        random_color = self.rng.choice(self.cmap)
        return {**base_style, "fill": random_color}


# Generate polygons using freud
voro = freud.locality.Voronoi()
system = freud.data.make_random_system(box_size=10, num_points=128, is2D=True)
polytopes = voro.compute(system).polytopes

# Iterate over our 2D polygons, adding a single face for each one.
shader = RandomColorShader(base_style=style)
scene = [
    svg3d.Mesh.from_vertices_and_faces(
        vertices, faces=[[*range(len(vertices))]], shader=shader
    )
    for vertices in polytopes
]

# Set up the camera and projection
pos_object = [0.0, 0.0, 0.0]  # "at" position
pos_camera = [0.0, 10.0, 8.0]  # "eye" position
vec_up = [0.0, -1.0, 0.0]  # "up" vector of camera.

z_near, z_far = 1.0, 200.0
aspect = 1.0
fov_y = 90.0

look_at = get_lookat_matrix(pos_object, pos_camera, vec_up=vec_up)
projection = get_projection_matrix(
    z_near=z_near, z_far=z_far, fov_y=fov_y, aspect=aspect
)

view = svg3d.View.from_look_at_and_projection(
    look_at=look_at,
    projection=projection,
    scene=scene,
)

# Render the scene
svg3d.Engine([view]).render("perspective-voronoi.svg")