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Jittery Scalar Bar in Saved GIF

See original GitHub issue

Bug Description:

When creating a GIF and rendering it onscreen, the scalar bar’s color map shows a smooth color gradient. However, after the animation is saved, the color gradient becomes blocky and jittery.

This appears to be an issue with either a new version of PyVista or a new version of one of its dependencies (potentially VTK). I believe this because I have previously saved GIF files that show a smooth scalar bar. However, I’ve been unsuccessful in pinpointing which version of PyVista or its dependencies causes the issues.

To Reproduce

The following code snippet is copied verbatim from the Create a GIF Movie page on the documentation. I also thought that the issue might be my graphics card drivers, but the example GIF displayed in the documentation also appears to suffer from the same problem.

import numpy as np

import pyvista as pv

x = np.arange(-10, 10, 0.25)
y = np.arange(-10, 10, 0.25)
x, y = np.meshgrid(x, y)
r = np.sqrt(x ** 2 + y ** 2)
z = np.sin(r)

# Create and structured surface
grid = pv.StructuredGrid(x, y, z)

# Create a plotter object and set the scalars to the Z height
plotter = pv.Plotter(notebook=False, off_screen=True)
plotter.add_mesh(grid, scalars=z.ravel(), smooth_shading=True)

# Open a gif
plotter.open_gif("wave.gif")

pts = grid.points.copy()

# Update Z and write a frame for each updated position
nframe = 15
for phase in np.linspace(0, 2 * np.pi, nframe + 1)[:nframe]:
    z = np.sin(r + phase)
    pts[:, -1] = z.ravel()
    plotter.update_coordinates(pts, render=False)
    plotter.update_scalars(z.ravel(), render=False)

    # must update normals when smooth shading is enabled
    plotter.mesh.compute_normals(cell_normals=False, inplace=True)
    plotter.render()
    plotter.write_frame()

# Closes and finalizes movie
plotter.close()

Screenshots Jittery Scalar Bar PyVista==0.30.0, VTK==9.0.3: wave_pyvista_0 30 0_vtk_9 0 3

PyVista==0.33.2, VTK==9.0.0: wave_pyvista_0 33 2_vtk_9 0 0

PyVista==0.33.2, VTK==9.0.3: wave_pyvista_0 33 2_vtk_9 0 3

PyVista==0.33.2, VTK==9.1.0: wave_pyvista_0 33 2_vtk_9 1 0

Smooth Scalar Bar Animation Made A Few Months Ago Using Different Code (PyVista and VTK Versions Unknown): Animate Output

System Information:

--------------------------------------------------------------------------------
  Date: Wed Jan 26 11:08:26 2022 Eastern Standard Time
                OS : Windows
            CPU(s) : 8
           Machine : AMD64
      Architecture : 64bit
       Environment : Python
       File system : unknown
        GPU Vendor : Intel
      GPU Renderer : Intel(R) HD Graphics P530
       GPU Version : 4.5.0 - Build 27.20.100.8681
  Python 3.8.8 (tags/v3.8.8:024d805, Feb 19 2021, 13:18:16) [MSC v.1928 64 bit
  (AMD64)]
           pyvista : 0.33.2
               vtk : 9.1.0
             numpy : 1.22.1
           imageio : 2.14.1
           appdirs : 1.4.4
            scooby : 0.5.11
        matplotlib : 3.5.1
--------------------------------------------------------------------------------