On 2D plane positive u values are displayed by the red color
(negative "tail" is not shown). v values are displayed by the green
color. This script uses simple explicit algorithm and
1024×1024 float32 textures with the Neumann (CLAMP_TO_EDGE)
boundary conditions. It makes 2 it time steps per frame.
In 3 seconds the script begins to plot the path of the spiral wave tip
(a small cycloid).