---
author: Stéphane Laurent
date: '2022-01-27'
highlighter: 'pandoc-solarized'
output:
  html_document:
    highlight: kate
    keep_md: no
  md_document:
    preserve_yaml: yes
    variant: markdown
tags: 'graphics, python, pyvista'
title: PyVista surface with dynamic colormap
---

I've just done this animation with **PyVista**:

![](https://github.com/stla/PyVistaMiscellanous/raw/main/HopfTorusMovingFlag.gif)

This is a Hopf torus with the so-called `flag` colormap as texture, but
this texture moves. Here is a [link to the full
code](https://github.com/stla/PyVistaMiscellanous/blob/main/HopfTorus_MovingFlag.py).

The trick is to normalize the scalars to $[0, 2\pi]$ and then to apply
the map $\sin(\cdot - t)$ to the scalars, with $t$ varying from $0$ to
$2\pi$. Let me show you another example, with an ellipsoid.

``` {.python}
from math import pi, sin
import numpy as np
import pyvista as pv

mesh = pv.Sphere(theta_resolution=200, phi_resolution=200)
mesh.scale((1, 0.5, 1), inplace=True) # ellipsoid
dists = mesh.points[:,2] # we take the third coordinates for the scalars
# then we map them to [0, 2*pi]:
dists = 2*pi * (dists - dists.min()) / (dists.max() - dists.min())

t_ = np.linspace(0, 2*pi, 100, endpoint=False) # the varying parameter
for i, t in enumerate(t_):
    pngfile = "pic%03d.png" % i
    pltr = pv.Plotter(window_size = [512, 256], off_screen = True)
    pltr.background_color = "#363940"
    pltr.set_focus([0, 0, 0])
    pltr.set_position((1.3, 0, 0))
    mesh["dist"] = np.sin(dists - t) # set the scalars - here is the "trick"
    pltr.add_mesh(
        mesh, smooth_shading = True, cmap = "flag", 
        show_scalar_bar = False, specular = 10
    )
    pltr.show(screenshot = pngfile)
```

This code produces the `png` files `pic000.png`, ..., `pic099.png`. Then
it remains to make a `gif` file from them, using e.g. **ImageMagick** or
**gifski**. And here is the result:

![](figures/Ellipsoid_DynamicFlag.gif)