LEGO-ifying Meshes

Project Overview

Procedural Houdini LEGO-ifier to convert any mesh into a model of LEGO pieces with a variety of shapes and sizes as well as accurate color. The LEGO pieces included are as follows:

• 2x2 brick
• 2x1 brick
• 1x1 brick
• sloped brick
• flat 1x1 brick
• flat 2x1 grill brick

The Houdini file includes controls for a user to customize brick size, frequency of "top" (flat) bricks being placed, and angular threshold for placing sloped bricks.

LegoDemo2.1.mp4

Process

• The group of points encompassing the mesh are determined as follows:
  • (1) VDBfrompolygons node -> ConvertVDB node to compute closed volume
  • (2) Pointsfromvolume node on bounding box of mesh
  • Create group of points by taking all points in (2) that are inside (1)
  • Blast all points outside of group
  • Attribute transfer Color and Normal point data from the mesh to the points
    • This requires using attribfrommap node and texture file to convert primitive material attribute to point Cd attribute
    • The normal data is corrected with VEX code (explained further)
• After getting the group of points, they are partitioned based on their location

• Partitioning "angled" points involves a VEX function determining the difference between the transferred normal data and {0, 1, 0}.
  • 
  • These angled points are then partitioned into 4 directions, based on their X and Z normal values
  • Their normals are adjusted so that the slope brick faces the correct direction
  • All un-angled points are corrected so their normals are {1, 0, 0}.
• Partitioning "top" points involves a VEX function querying every point and whether a point was above it or below it
• Prioritizing larger bricks over smaller bricks requires a for-loop
  • Iterates over each point, adds a single point for each desired block-shape bounding box that fits
  • For example: iterate over points, if point fits a 2x2 brick along with 3 others, it is added to the final group & the other 3 are removed
  • The desired brick is then copied to this group with copytopoints node
• Node parameters:
  • Brick Size is a parameter for particle separation from Pointsfromvolume node
    • Range: 0-0.3
  • Slope Threshold is a parameter for how far the normal separation from {0, 1, 0} has to be for the slope brick to appear
    • Range: 0-1
  • Top-Brick Percentage is a parameter for how many of the "top" bricks appear as opposed to an empty space
    • Range: 0-1

Source Files

https://drive.google.com/file/d/1Coxo1xLHG-ALQGJ5SC2TZj1ZmM-i4lcl/view?usp=drive_link