comfyui_pcg docs

Tutorial 3: attributes and wrangle#

Attributes are named values stored per point, per primitive, per vertex or once per geometry (detail). This tutorial creates two point attributes, edits one with a Wrangle expression, moves it from points to faces, colours by it, and turns a comparison on it into a group that drives an extrusion.

Grid extruded and coloured by the height attribute

Load it#

Drag example_workflows/tutorial_03_attributes_wrangle.json onto the ComfyUI canvas and press Queue. No model files or other custom nodes are needed.

Step by step#

  1. Grid (PCG) makes a flat 12 x 12 grid with 61 x 61 points.
  2. Attribute Create (PCG) ("dist = length(@P)") creates the float point attribute dist. Use Expression is on, so the value comes from the expression length(@P): the distance of each point from the origin.
  3. Attribute Noise (PCG) ("height = noise") writes noise into a new attribute instead of moving the points: Attribute Names is height, the type is float and the range is zero_to_one, so every point gets a value between 0 and 1.
  4. Wrangle (PCG) ("Fade towards the edge") runs one line of code over all points at once: 
    @height = @height * (1 - smoothstep(3.0, 6.0, @dist))

    @name reads or writes an attribute; the code is Python syntax evaluated on whole numpy arrays, so there is no per-point loop. Points further than 6 from the centre end up with height 0.

  5. Attribute Promote (PCG) ("height: points to faces") averages height from the points of each face into a primitive attribute (and, with the default Delete Original, removes the point version). The next two nodes work on faces.
  6. Group Create (PCG) ("Group 'tall'") uses the base pattern @height > 0.35 to put the matching faces into the primitive group tall. Any Group field in the plugin accepts this kind of @attribute comparison.
  7. PolyExtrude (PCG) ("Raise 'tall' by its height") extrudes only the group tall, each face separately (individual). Local Attributes is on with Distance Scale height, so each face moves by distance 3 times its own height.
  8. Color (PCG) ("Colour by height") uses the mode Ramp from Attribute on the primitive attribute height. The range is computed automatically and mapped through the default blue-green-red ramp.
  9. Geometry Preview (PCG) (Studio look) and Viewport (PCG) show the result.

Worth tweaking#

NodeParameterEffect
Group 'tall'baseTry @height > 0.6, or @height > 0.35 & @height < 0.5, to change which faces rise.
height = noiseelement_size_*, rand_seed, noise_typeSize and layout of the noise blobs.
Fade towards the edgecodeChange the fade radii, or add a second line such as @height = @height ** 2 for sharper peaks.
Raise 'tall' by its heightdistanceMultiplier for the attribute; inset adds a gap between neighbouring columns.
Colour by heightramp, auto_rangeYour own colour ramp, or a fixed input range.

To see the attribute values at any step, wire that node into a Geometry Spreadsheet (PCG) node: it shows the point, primitive, vertex and detail attributes in tables on the node.

See also#