The ferox-scene API uses the Entreri component framework to define a number of components that can be combined to describe entities within a scene. \u00a0Many properties of these components are vector or matrix types, such as direction, position, transform, color, etc. \u00a0I needed a solution that had the following features:<\/p>\n
To solve problem #1, I implemented custom Properties that wrap a DoubleProperty but provide getters and setters using the appropriate math types. \u00a0At the Property level, they getters require a result type but I was on the right path to solving #2 and #3.<\/p>\n
The math Properties were implemented very similarly and fit this general pattern:<\/p>\n
@Factory(FooProperty.Factory.class)\r\npublic class FooProperty implements Property {\r\n private final DoubleProperty realData; \r\n\r\n public Foo get(int index, Foo result) { } \r\n\r\n public void set(int index, Foo value) { } \r\n\r\n @Attribute\r\n public static @interface DefaultFoo {\r\n \/\/ attributes for default Foo's\r\n }\r\n\r\n \/\/ Factory implementation to create FooProperties\r\n public static class Factory implements PropertyFactory<FooProperty> { }\r\n}<\/pre>\nHere is an example of how a Vector3 could be stored as a property:<\/p>\n
@Factory(Vector3Property.Factory.class);\r\npublic class Vector3Property {\r\n \/\/ 3 elements for x, y, z\r\n private final DoubleProperty values = new DoubleProperty(3); \r\n\r\n public void get(int index, Vector3 v) {\r\n \/\/ sets the state of v to match the indexed data\r\n v.set(values.getIndexedData(), index * 3);\r\n }\r\n\r\n public void set(int index, Vector3 v) {\r\n \/\/ gets the state of v into the indexed data\r\n v.get(values.getIndexedData(), index * 3);\r\n }\r\n\r\n @Attribute\r\n public static @interface DefaultVector3 {\r\n double x();\r\n double y();\r\n double z();\r\n }\r\n\r\n public static class Factory implements PropertyFactory<Vector3Property> {\r\n \/\/ implementation checks for DefaultVector3 attribute for\r\n \/\/ initial value assignment\r\n }\r\n}<\/pre>\nThis provides a convenient wrapper around a DoubleProperty and provides us with an annotation to set the default value of each vector to separate x, y, and z values. However, it does not help with reduced instantiation because it requires an input Vector3 to get or set values in the property.<\/p>\n
By using the protected onSet(int)\u00a0method in ComponentData implementations, we can add an unmanaged Vector3 field to a component type that is cached, and is kept in-sync with the property with the set listener method.<\/p>\n
public class MyComponent extends ComponentData<MyComponent> {\r\n @DefaultVector3(x=1.0, y=0.0, z=1.0);\r\n private Vector3Property vector;\r\n\r\n @Unmanaged\r\n private final Vector3 cache = new Vector3();\r\n\r\n \/\/ Use @Const to tell programmers not to mutate data.\r\n \/\/ Alternatively expose a read-only interface.\r\n public @Const Vector3 getVector3() {\r\n return cache;\r\n }\r\n\r\n public void setVector3(Vector3 v) {\r\n cache.set(v);\r\n vector.set(getIndex(), v);\r\n }\r\n\r\n @Override\r\n protected void onSet(int index) {\r\n vector.get(index, v);\r\n }\r\n}<\/pre>\nWith all of this together, you can create many Component<MyComponent> and the vectors will be automatically packed into a hidden double array. \u00a0This provides good cache locality. \u00a0Using the wrapper Vector3Property and the onSet() event listener in MyComponent, the final exposed interface is a convenient Vector3 instance. \u00a0Even with all of this, only a single instance of Vector3 is required for each instance of MyComponent.<\/p>\n
Because ComponentData instances are used as fly-weight objects over the identifying Components, this makes iterating over all MyComponent’s require minimal object creation overhead.<\/p>\n
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