feat(FXC-4425) Adding plot function for charge

[marc-flex]

Currently we have basically two options of platting our simulation object for HeatChargeSimulation object that involve using the property argument in the plot_property function:

• property=”heat_conductivity” → plots the structures greyed by thermal conductivity and shows thermal BCs
• property=”electric_conductivity” → plots structures greyed by electric conductivity and shows electric BCs

In the case of Charge simulations, we don’t have a value for conductivity in the SemiconductorMedium and so the function fails to plot the strucutres.

The idea is to include a new property that allows us to plot the structures and show electric BCs

Greptile Overview

Greptile Summary

Adds a new "charge" property option to plot_property() in HeatChargeSimulation, allowing visualization of charge simulations that use SemiconductorMedium (which lacks a conductivity value). This addresses a limitation where property="electric_conductivity" would fail for such simulations.

• Extends plot_property(), plot_boundaries(), and plot_sources() to handle "charge" property
• Renders charge simulations with structures in gray fill with black edges (no conductivity-based grayscale)
• Disables colorbar for charge plots since there's no conductivity value to display
• Shows electric boundary conditions and charge sources when property="charge"
• Refactors charge_tolerance fixture from class-level to module-level for broader test reuse
• Missing CHANGELOG entry for this user-facing feature (per custom rule)

Confidence Score: 4/5

• This PR is safe to merge - straightforward feature addition with proper validation and test coverage.
• The implementation is well-structured with appropriate guards for simulation type validation, clear branching logic, and comprehensive test coverage including negative cases. Minor concern: dead code in _get_structure_heat_charge_property_plot_params and missing CHANGELOG entry.
• No files require special attention. The implementation is consistent across all modified files.

Important Files Changed

File Analysis

Filename	Score	Overview
tidy3d/components/tcad/simulation/heat_charge.py	4/5	Adds "charge" property support to plot_property() and related methods (plot_boundaries, plot_sources, source_bounds), enabling visualization of charge simulations with appropriate boundary conditions and sources.
tidy3d/components/scene.py	4/5	Adds "charge" property to type hints and handles the new property in plot_heat_charge_property, heat_charge_property_bounds, and related methods with appropriate styling (gray fill, black edge).
tests/test_components/test_heat_charge.py	5/5	Adds test_plot_property_charge test and refactors charge_tolerance fixture from class-level to module-level scope for broader reuse.

Sequence Diagram

sequenceDiagram
    participant User
    participant HeatChargeSimulation
    participant Scene
    participant PlotMethods

    User->>HeatChargeSimulation: plot_property(property="charge", z=0)
    HeatChargeSimulation->>HeatChargeSimulation: _get_simulation_types()
    
    alt CHARGE not in simulation_types
        HeatChargeSimulation-->>User: ValueError
    end
    
    HeatChargeSimulation->>Scene: plot_heat_charge_property(property="charge")
    Scene->>Scene: heat_charge_property_bounds(property="charge")
    Scene-->>Scene: return (0, 1)
    
    loop for each structure
        Scene->>Scene: _plot_shape_structure(property="charge")
        Scene->>Scene: _get_structure_plot_params(property="charge")
        Note over Scene: Apply edgecolor="k", linewidth=1
    end
    
    HeatChargeSimulation->>PlotMethods: plot_sources(property="charge")
    Note over PlotMethods: Filter ChargeSourceTypes
    
    HeatChargeSimulation->>PlotMethods: plot_boundaries(property="charge")
    Note over PlotMethods: Filter ElectricBCTypes
    
    HeatChargeSimulation-->>User: matplotlib.axes

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Context used:

• Rule from dashboard - Require a changelog entry for any PR that is not purely an internal refactor. (source)

[Copilot]

Pull request overview

This PR adds support for plotting charge simulations by introducing a new property="charge" option to the plot_property function. Previously, plotting charge simulations with SemiconductorMedium failed because these mediums don't have a conductivity value. The new option plots structures with fixed styling (lightgray fill with black borders) and displays electric boundary conditions.

Key Changes:

• Added "charge" as a valid property option for plotting functions
• Implemented special handling for charge simulations that bypasses conductivity-based coloring
• Added validation to ensure property="charge" is only used with charge simulations

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 2 comments.

File	Description
tidy3d/components/tcad/simulation/heat_charge.py	Updated plot_property to accept "charge" property, disable colorbar for charge, add validation logic, and filter boundaries/sources appropriately for charge simulations
tidy3d/components/scene.py	Added "charge" property handling in plotting functions with type hints, custom plot parameters (lightgray/black), and property bounds
tests/test_components/test_heat_charge.py	Added test coverage for the new charge plotting functionality and refactored charge_tolerance fixture to module scope

Comments suppressed due to low confidence (1)

tidy3d/components/scene.py:1722

• When property="charge" and cbar=True, a colorbar will be added with an empty label. Since the "charge" property doesn't use grayscale coloring (it uses fixed lightgray), the colorbar is not meaningful. Consider adding a condition to skip the colorbar when property == "charge":

if cbar and property != "charge":
    # ... existing colorbar code

        if cbar:
            label = ""
            if property == "heat_conductivity":
                label = f"Thermal conductivity ({THERMAL_CONDUCTIVITY})"
            elif property == "electric_conductivity":
                label = f"Electric conductivity ({CONDUCTIVITY})"
            self._add_cbar(
                vmin=property_val_min,
                vmax=property_val_max,
                label=label,
                cmap=STRUCTURE_HEAT_COND_CMAP,
                ax=ax,
            )

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Diff Coverage

Diff: origin/develop...HEAD, staged and unstaged changes

• tidy3d/components/scene.py (100%)
• tidy3d/components/tcad/simulation/heat_charge.py (100%)

Summary

• Total: 12 lines
• Missing: 0 lines
• Coverage: 100%