Rule file import—ArcGIS CityEngine Resources

Importing a rule file makes all rules, attributes and functions of the imported rule file available under the given prefix, see CGA Reference.

The following rule files both define a Facade rule, each one is texturing a building facade in a different way:

# -- facade1.cga

actualFloorHeight = scope.sy/rint(scope.sy/4)
actualTileWidth   = scope.sx/rint(scope.sx/4)
    
Facade --> setupProjection(0, scope.xy, 2, 2)
           projectUV(0)
           texture("facade1.jpg")

# -- facade2.cga

actualFloorHeight = scope.sy/rint(scope.sy/6)
actualTileWidth   = scope.sx/rint(scope.sx/4)
    
Facade --> setupProjection(0, scope.xy, 3, 2)
           projectUV(0)
           texture("facade2.jpg")

The next rule file contains a Lot rule that creates a building mass and splits it into its side faces and a roof face:

# -- structure.cga

// the attribute height will be overridden by the
// attribute height from "main.cga" if this rule
// file is included. Thus if this rule file is
// used standalone, the buildings will be of height
// 100, if this rule file is included by "main.cga",
// the buildings will be of height 200.

attr height = 5

Lot --> extrude(height)
        comp(f) { side : Facade | top : Roof. }

Finally, the main rule file with Lot start rule imports both facade rules and the structure rule.

The Lot rule calls the Lot rule in structure.cga using the st. namespace.
The attribute height in structure.cga is overwritten by the attribute height in main.cga. Therefore, a building of height 10 is created.
Note:
If structure.cga was used standalone, a building of height 5 would be created
The Facade rule for structure.cga is defined in main.cga. It calls the Facade rule of either facade1.cga or facade2.cga.

# -- main.cga

// define an attribute "height", potentially
// overriding the same attribute in imported
// rule files.

import f1 : "facade1.cga"
import f2 : "facade2.cga"
import st : "structure.cga"

attr height = 10

Lot --> st.Lot

st.Facade --> 50% : f1.Facade else : f2.Facade

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