Translation: Blender Instance Attributes Grass Tuft

Source

Source file: https://download.blender.org/demo/geometry-nodes/instance_attribtues.blend
Source group: Grass Tuft Generator
Geometry Script recreation: examples/geometry_script/blender_instance_attributes.py

Why This Graph

This is the first verified scatter/instance/deform sample in the corpus. It is small enough to translate directly, but it uses the important grown-up trick: capture instance state before realization, then use that remembered value to deform the realized geometry.

Graph Map

Source group: Grass Tuft Generator

Geometry Script group: VG Grass Tuft Generator

Mechanism:

Build a triangular-fan disc, subdivide it, and use it as the scatter nursery.
Compute radial distance from Position, remap it through Map Range, and reuse that falloff for both point density and instance scale.
Build one blade as a five-point vertical mesh line, convert it to a curve, and taper it with Set Curve Radius from 1 - Spline Parameter.Factor.
Distribute points on the disc with Poisson spacing controlled by thickness and density.
Instance the tapered blade on the points, scale each instance by radial falloff, then capture the instance Position on the INSTANCE domain.
Realize the instances. The captured root position survives as the center, radius sample, and tangent-axis basis for curl.
Rotate each realized blade position around a tangent axis. Curl grows along blade length and is modulated by distance from the tuft center.
Convert curled curves to mesh with a triangular profile. If a radius attribute exists, use it as the profile scale.

Metaphor: the disc is a nursery tray, the points are planting holes, each instance carries a root tag, and realization turns the tray into individual blades. Curl reads the root tag to bend every blade around its own base instead of around the world origin.

Verification

Run:

& 'C:\Program Files (x86)\Steam\steamapps\common\Blender\blender.exe' --background '.\experiments\source-blends\blender-instance-attributes.blend' --python '.\tools\verify_instance_attributes_translations.py'

Results from Blender 5.1.1:

Case	Source vertices	Translated vertices	Delta	Status
default	45	45	0.0	accepted
wider curlier seeded	165	165	0.0	accepted

Both cases also match edge counts, polygon counts, and smooth-face flags.

Lessons

Scatter graphs often have three separable layers: seed surface, point field, and instance body. Keep them named in script.
A field can be reused across domains intentionally. Here, radial falloff controls both scatter density and final instance scale.
Captured instance attributes must be explicit under Blender 5.1. Geometry Script's generic capture_attribute(...) call did not create the required capture item here; the verified script uses the explicit _capture_attribute_item(...) helper.
nodes_to_script recovered the wiring and defaults well enough to debug the translation, but its output remains a transcript, not accepted style.

3.1 KiB Raw Blame History