Rhino 3D Tip: Building Robust, Reusable GhPython Components for Grasshopper

Turn Grasshopper scripts into reusable, shareable tools with GhPython.

• Structure your component
  • Encapsulate core logic in a clean compute() function; keep inputs/outputs thin and descriptive.
  • Use Rhino document tolerances for robust geometry: RhinoDoc.ActiveDoc.ModelAbsoluteTolerance.
  • Keep previews light—output only what you need. Heavy preview can slow large definitions.
• Inputs and outputs that scale
  • Name inputs clearly, set sensible defaults, and add descriptions so the User Object stays self-documenting.
  • Choose access: Item, List, or Tree. For Trees, use ghpythonlib.treehelpers to convert between DataTree and nested lists.
  • Return consistent data types. If sometimes you output a single item and other times a list, wrap singletons in a list for predictability.
• Performance and stability
  • Cache expensive results with scriptcontext.sticky keyed by small hashes of the inputs.
  • Fail fast with clear runtime messages: AddRuntimeMessage(Warning/Error). This saves time downstream.
  • Guard external-library imports with try/except and provide guidance if dependencies are missing.
• Packaging for reuse
  • Right–click the GhPython component > Create User Object. Name, Category, and Subcategory matter—keep them consistent across your library.
  • Add an icon and a concise description. Note any plugin dependencies in the description.
  • Version your tools. Include a short version string on the component message for quick identification.
• Debugging and quality
  • Use print for quick checks and the Profiler widget for hotspots.
  • Validate geometry: IsValid, IsClosed, orientation, and domain checks before operations like Offset/Loft/Boolean.
  • Test with both simple and pathological inputs (tiny features, overlapping curves, mixed units).

# GhPython template: robust, cache-aware, tree-friendly
import Rhino
import scriptcontext as sc
import ghpythonlib.treehelpers as th
from Grasshopper import Kernel as ghk

def compute(crvs, dist):
    tol = Rhino.RhinoDoc.ActiveDoc.ModelAbsoluteTolerance
    valid = [c for c in crvs if c and c.IsValid]
    if not valid:
        ghenv.Component.AddRuntimeMessage(
            ghk.GH_RuntimeMessageLevel.Error, "No valid curves supplied."
        )
        return []
    results = []
    for c in valid:
        # Simple example: planar offset (if planar)
        ok, plane = c.TryGetPlane()
        if not ok:
            ghenv.Component.AddRuntimeMessage(
                ghk.GH_RuntimeMessageLevel.Warning, "Non-planar curve skipped."
            )
            continue
        offs = c.Offset(plane, dist, tol, Rhino.Geometry.CurveOffsetCornerStyle.Sharp)
        if offs: results.extend(offs)
    return results

# Input handling: supports list or tree
crv_list = th.tree_to_list(Curves, purge_empty=True) if hasattr(Curves, "Branches") else Curves

# Simple cache key
key = (len(crv_list), round(Distance, 6))
if sc.sticky.get("ghp_offset_key") == key:
    OUT = sc.sticky.get("ghp_offset_val")
else:
    OUT = compute(crv_list, Distance)
    sc.sticky["ghp_offset_key"] = key
    sc.sticky["ghp_offset_val"] = OUT

ghenv.Component.Message = "v1.0 GhPy"

• Pro tips
  • Use Named Groups and consistent Categories so your tools feel like a coherent plugin.
  • Document inputs and edge cases in the component description so teammates adopt it faster.
  • When performance matters, push heavy loops into RhinoCommon geometry calls rather than pure Python.

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