Context (and occlusion) queries

List of available context queries

Context queries are functions that return information about contextual shapes in the environment of the current shape. Occlusion queries are special context queries that return information about the mutual intersection of geometries.

Occlusion queries

bool func()

bool func(target-selector)

bool func(target-selector, label)

inside Returns true if current shape is inside another shape geometry.
overlaps Returns true if current shape overlaps another shape geometry.
touches Returns true if current shape touches another shape geometry.

General context queries

float func(target-selector, label, ...)

minimumDistance Returns distance of current scope to scope of another labeled shape.
contextCompare Returns the rank of the current shape geometry among other labeled shape geometries according to a specific comparator.
contextCount Returns the number of labeled shapes in the environment.

Target selectors

For all functions the parameter target-selector determines what the current geometry is tested against and can either be intra, inter, or all. Thus, the current geometry can be tested against geometries of shapes

If no target-selector is given (occlusion queries), all is set as default.

Specifics on inter context

Neighborhood distance

The initial shapes within a user-defined neighborhood distance to the bounding box of the current intial shape are taken into account. Distances are available for

The defaults are reasonable for most cases. The distances can be modified in the procedural runtime preferences and are stored per scene.

Inter context queries possibly need to consider many initial shapes in the envronment and are computationally more expensive than intra context queries. If you aim to solely check for intra, specify the intra target selector in order to avoid unnecessary overhead by inter.

Scenarios

Whether inter context queries consider initial shapes in their environment depends on the scenario the shapes belong to:

The contextural influence of shapes is determined by their assigned scenarios and not by their current visibility in the viewport.

Two-pass generation process

At the time context queries are evaluated not all geometries that could be relevant have been generated. Additionally, context queries are typically applied in the conditional part of a rule. Their result can influence the generated model and, therefore, in turn could change the result of the queries. Because of that, a special deterministic two-pass generation process is performed for intra context:

  1. Shape trees are generated with intra queries returning a default value:
    inside false
    overlaps false
    touches false
    minimumDistance infinity
    contextCompare 0
    contextCount 0
  2. The derivation is re-started. This time intra context queries are evaluated by testing against the previously generated geometries of step 1.

In the case of inter context, a deterministic behavior is achieved by similiar means. All inter queries of models in the neighborhood of the current initial shape return default values. The described method proved to be satisfactory in most practical use case scenarios.

Shapes that are generated conditionally by a non-default case in an intra occlusion query are not considered for intra occlusion. Shapes that are generated conditionally by a non-default case in an inter occlusion query are not considered for inter occlusion.

Related

Examples

Labels


context label
	
	
	
Lot --> label("label")
        print(contextCount(intra, "label"))
        label("label")
	
In a first generation process each label() operation creates a labeled copy of the current shape. In the second pass, the contextCompare query function is used to retrieve the number of all shapes with label "label".

Conditions


context conditional
Lot   --> comp(f) { all : extrude(10) Test }

Test  --> case overlaps(intra) :                         Red
          else :                 s('2,'1,'2) center(xyz) Green
		  
Red   --> color(1,0,0)
Green --> color(0,1,0)		  
	
In this example the Lot rule is applied to an initial single shape with two faces (intra occlusion). The default false case of the overlaps() enlarges the extruded volume. Therefore, the geometry intersects the neighboring extruded volume, and the overlaps() query returns true. The enlarged occluder shape is not visible.
	
	
	
Test --> case overlaps(intra) : s('2,'1,'2) center(xyz) Red
         else :                                         Green
	
In contrast, if we enlarge the extruded volume in the non-default true case, the overlaps() query returns false

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