Isolines in `show_slice`

[dvd101x]

Hi,

This is not an issue, just a proposal to include isolines as other 2D representations of SDF.

Change this

To something like this

The change in code is not that much, this is an example.

def show_slice(*args, **kwargs):
    import matplotlib.pyplot as plt
    from matplotlib.colors import TwoSlopeNorm
    a, extent, axes = sample_slice(*args, **kwargs)
    norm = TwoSlopeNorm(vmin=a.min(), vcenter=0, vmax=a.max())
    im = plt.imshow(a, extent=extent, origin='lower', cmap="PRGn", norm=norm)
    plt.contour(a, colors='white', alpha=0.5, extent=extent)  # Add semi-transparent isolines
    plt.contour(a, levels=[0], colors='black', extent=extent)  # Add isoline at 0
    plt.xlabel(axes[0])
    plt.ylabel(axes[1])
    plt.colorbar(im)
    plt.show()

The idea is to use a diverging color map centered at 0, add isonlines shown in white and add a single isoline shown in black representing the boundary of the solid.