Designing Custom Subcomponents

Prev: Part 9: Routing

Designing your own subcomponents in PyMFCAD is straightforward. You create a new class that inherits from Component, define geometry in __init__, and use self. for all operations. This lets you encapsulate reusable device features like mixers, valves, or junctions.

Use the template here: Custom Component Template.

Step 1 — Create a custom class

Subcomponents should subclass Component (or VariableLayerThicknessComponent when needed).

Key requirements:

Implement __init__ with parameters you want to expose.
Save constructor arguments in self.init_args and self.init_kwargs.
Call super().__init__() with size, position, and resolution.

Step 2 — Define geometry and ports

Inside __init__, use self.add_label, self.add_void, self.add_bulk, self.add_port, self.add_subcomponent, or any other Component function to define the subcomponent.

Step 3 — Save it as a reusable module

Place your class in a standalone Python file so you can import it in any project.

Example — Y‑junction subcomponent

Below is a minimal example of a Y-junction mixer subcomponent:

import inspect
from pymfcad import Component, Port, Color, Cube, Polychannel, PolychannelShape

class YJunctionMixer(Component):
    """
    Simple Y-junction mixer with two inlets and one outlet.
    """

    def __init__(self, channel_size=(8, 8, 6), channel_margin=(8, 8, 6, quiet=False)):
        # Store constructor arguments for equality comparison.
        frame = inspect.currentframe()
        args, _, _, values = inspect.getargvalues(frame)
        self.init_args = [values[arg] for arg in args if arg != "self"]
        self.init_kwargs = {arg: values[arg] for arg in args if arg != "self"}

        # Initialize the base Component
        super().__init__(
            size=(
                4 * channel_size[0],
                2 * channel_size[1] + 3 * channel_margin[1],
                channel_size[2] + 2 * channel_margin[2],
            ),
            position=(0, 0, 0),
            px_size=0.0076,
            layer_size=0.01,
            quiet=quiet
        )

        self.add_label("bulk", Color.from_name("gray", 255))
        self.add_label("void", Color.from_name("aqua", 255))

        # Add a simple Y-shaped channel using Polychannel
        y_shape = Polychannel(
            [
                PolychannelShape(
                    "cube",
                    position=(0, channel_margin[1], channel_size[2]),
                    size=(0, channel_size[1], channel_size[2]),
                ),
                PolychannelShape(
                    "cube",
                    position=(4 * channel_size[0], 1 * channel_margin[1], 0),
                    size=(0, channel_size[1], channel_size[2]),
                ),
                PolychannelShape(
                    "cube",
                    position=(-4 * channel_size[0], 1 * channel_margin[1], 0),
                    size=(0, channel_size[1], channel_size[2]),
                ),
            ]
        )
        y_shape.translate(
            (
                0,
                channel_size[1] / 2,
                channel_margin[2] / 2,
            )
        )
        self.add_void("y_channel", y_shape, label="void")

        self.add_bulk(
            "BulkShape",
            Cube(self._size, center=False),
            label="bulk",
        )

        # Add ports: two inlets and one outlet
        self.add_port(
            "inlet1",
            Port(
                Port.PortType.IN,
                (0, channel_margin[1], channel_size[2]),
                channel_size,
                Port.SurfaceNormal.NEG_X,
            ),
        )
        self.add_port(
            "inlet2",
            Port(
                Port.PortType.IN,
                (0, channel_size[1] + 2 * channel_margin[1], channel_size[2]),
                channel_size,
                Port.SurfaceNormal.NEG_X,
            ),
        )
        self.add_port(
            "outlet",
            Port(
                Port.PortType.OUT,
                (
                    4 * channel_size[0],
                    channel_size[1] + channel_margin[1],
                    channel_size[2],
                ),
                channel_size,
                Port.SurfaceNormal.POS_X,
            ),
        )


if __name__ == "__main__":
    YJunctionMixer().preview()

Y Junction

This pattern can be adapted for any custom subcomponent. Define your geometry and ports inside the class, then import and reuse it across devices.

Checkpoint: In the visualizer, you should see a Y‑shaped channel inside a rectangular bulk.

Next: Part 11: Creating Your First Slicable Device