03 - Bulb fieldlines example “twinfield”

This example shows one of the ways to plot fieldlines: here the fieldlines values are used to modify the original layer values before applying the colormap. Notice the use of calc_orbit and backshift` during the calculation.

The location is around the 1/3 main bulb.

Reference: fractalshades.models.Mandelbrot

import os

import fractalshades as fs
import fractalshades.models as fsm
import fractalshades.colors as fscolors
from fractalshades.postproc import (
    Postproc_batch,
    Continuous_iter_pp,
    Fieldlines_pp,
    Raw_pp,
)
from fractalshades.colors.layers import (
    Color_layer,
    Bool_layer,
    Virtual_layer
)

def plot(plot_dir):
    """
    Using field lines : a shallow zoom in the Seahorses valley
    Coloring based on continuous iteration + fieldlines
    """
    # Define the parameters for this calculation
    x = -0.10658790036
    y = 0.96946619217
    dx = 0.6947111395902539
    nx = 2400
    projection = fs.projection.Cartesian()

    calc_name="mandelbrot"
    colormap = fscolors.cmap_register["classic"]

    # Run the calculation
    f = fsm.Mandelbrot(plot_dir)
    f.zoom(x=x, y=y, dx=dx, nx=nx, xy_ratio=1.0,
           theta_deg=0., projection=projection)
    f.calc_std_div(
        calc_name=calc_name,
        subset=None,
        max_iter=5000,
        M_divergence=100.,
        epsilon_stationnary= 0.001,
        calc_orbit=True,
        backshift=3
    )

    # Plot the image
    pp = Postproc_batch(f, calc_name)
    pp.add_postproc("cont_iter", Continuous_iter_pp())
    pp.add_postproc("interior", Raw_pp("stop_reason", func="x != 1."))
    pp.add_postproc("fieldlines",
                Fieldlines_pp(n_iter=4, swirl=0., endpoint_k=0.8))

    plotter = fs.Fractal_plotter(pp)
    plotter.add_layer(Bool_layer("interior", output=False))
    plotter.add_layer(Color_layer(
            "cont_iter",
            func="np.log(x)",
            colormap=colormap,
            probes_z=[0.4, 2.4],
            output=True
    ))
    plotter.add_layer(Virtual_layer("fieldlines", func=None, output=False))
    plotter["cont_iter"].set_mask(plotter["interior"], mask_color=(0., 0., 0.))

    # This is the line where we indicate that coloring is a combination of
    # "Continuous iteration" and "fieldines values"
    plotter["cont_iter"].set_twin_field(plotter["fieldlines"], -0.4)
    plotter.plot()


if __name__ == "__main__":
    # Some magic to get the directory for plotting: with a name that matches
    # the file or a temporary dir if we are building the documentation
    try:
        realpath = os.path.realpath(__file__)
        plot_dir = os.path.splitext(realpath)[0]
        plot(plot_dir)
    except NameError:
        import tempfile
        with tempfile.TemporaryDirectory() as plot_dir:
            fs.utils.exec_no_output(plot, plot_dir)