BuildingProceduralGeneration

From OpenCity

BuildingProceduralGenerationOverview

Contents 1 Goal 1.1 Input 1.2 Ouput 1.3 Postprocessing 2 Concept 2.1 Shape grammar 2.2 Contextual Shape grammar 2.3 Condition for apply rules 2.4 Spapping 2.5 Building generation 2.6 Texture generation

Goal

Build a procedural building generator.

Input

A limited set of parameter:

• a rectangular ground shape: width an height
• a seed
• an architectural style
• a game level (inhabitants or workers)

And data:

• grammar rules
• basic shape
• basic textures tiles

Ouput

• Shapes with texture
• LOD information

Postprocessing

Result model need be used in realtime render:

• remerge shape and texture when possible

Concept

Shape grammar

Axiome:

• foot-print
• mass model

Set of rules classed by priority. Apply rules if no rules of lower priority match. Priority set can be used to determine LOD.

• Shape: symbol, geometry, attributes (position and size aka scope), and terminal or non-terminal symbol
• Rules: replace (children) a non terminal shape by others, condition, probability

Rule operations (relative to mother shape):

• Translation T(x,y,z)
• Rotation R(x,y,z)
• Set Scope size S(w,h,l)
• Push and Pop scope contexte [ ]
• Instantiate Primitive (box, cylinder, etc) I(box)
• Split by axis Split(axis,[part size (absolute or relative) and symbol])
• Repeat by axis Tile(axis, part size and symbol)
• Component by split type Component(splitType, symbol)
• Roof Roof(roof type, angle)
• Empty

Function:

• current scope size Socpe.[w|y|z]
• +-*/
• random

Contextual Shape grammar

Condition for apply rules

• Occlusion test of current shape agains other Occlusion(agains all|leafs|all excepts parents, [distance]), returns none, partial or full
• Visibility (sightlines) test point of view (as street) Visible(placeType)

Spapping

Adapt rule to embded snap plane:

• Split: allow addition of snap planes betwen generated part Snap(axis)
• Repeat: allow addition of snap planes betwen generated part Snap(axis)

Affect Split and Repeat operations if crossed by snap

• Split: snap closest split axis
• Repeat: cut into two parts around snap and compute repeat on parts

Building generation

Applying grammar to produce tree of shapes. Only leafs are part of final model. Each tree node is contextual, have 3d matix situation.

Texture generation